Advanced phytochemical analysis of herbal tea in China

Journal of Chromatography A, 1313 (2013) 2–23

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Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma

Review

Advanced phytochemical analysis of herbal tea in China J. Zhao 1 , J.W. Deng 1 , Y.W. Chen 1 , S.P. Li ∗ The Key Laboratory of Quality Research in Chinese Medicine, and Institute of Chinese Medical Sciences, University of Macau, Macao

a r t i c l e

i n f o

Article history: Received 6 May 2013 Received in revised form 19 June 2013 Accepted 8 July 2013 Available online 12 July 2013 Keywords: Phytochemical analysis Herbal tea Sample preparation Chromatography Mass spectrometry

a b s t r a c t Herbal tea is a commonly consumed beverage brewed from the leaves, flowers, seeds, fruits, stems and roots of plants species rather than Camellia sinensis L., which has been widely used for health care and diseases prevention for centuries. With the increasing consumption of herbal tea, a number of public health issues e.g., efficacy, safety and quality assurance have attracted concern. However, to date, there is no a review focus on herbal tea. Phytochemical analysis, as a key step to investigate the chemical composition of herbal tea and ensure the quality, is very important. In this review, we summarized and discussed the recent development (2005–2012) in phytochemical analysis of herbal tea commonly used in China. © 2013 Elsevier B.V. All rights reserved.

Contents 1. 2.

3.

4.

5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Conventional methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Ultrasonic extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Microwave-assisted extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Pressurized liquid extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5. Supercritical fluid extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6. Solid phase microextraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7. Solid phase extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of processing on components in herbal tea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Adjuvant materials processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phytochemical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Gas chromatography and hyphenated techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Liquid chromatography and hyphenated techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1. Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2. Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Electromigration techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Ambient mass spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Future outlooks and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 3 3 5 5 6 6 6 6 6 6 8 8 8 8 10 10 16 17 18 21 21 21

1. Introduction

∗ Corresponding author. Tel.: +853 8397 4692; fax: +853 2884 1358. E-mail addresses: [email protected], [email protected] (S.P. Li). 1 The authors contributed equally to this work. 0021-9673/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.chroma.2013.07.039

Herbal tea, i.e., herbal infusion or herbal tisane, is a commonly consumed beverage brewed from the leaves, flowers, seeds, fruits, stems or roots of plant species rather than Camellia sinensis L., and it has been used for health care and diseases prevention for

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

3

worldwide. With the increasing consumption of herbal tea, a number of public health issues have been raised [47–49]. Therefore, quality control is crucial for ensuring the safety and efficacy of herbal tea. Unfortunately, there is no review related to herbal tea to date. Sure, we reviewed the development of phytochemical analysis for medicine and food dual purposes plants used in China in 2011 [5]. In this review, we summarized and discussed the recent development of phytochemical analysis for herbal tea commonly used in China, but the materials related to medicine and food dual purposes plants were not considered except the updated publications. 2. Sample preparation Sample preparation is the crucial first step in the process of phytochemical analysis because it is necessary to extract and isolate the desired chemical components from matrices for further determination and characterization. In the last decade, the major sample preparation techniques for phytochemical analysis of medicinal plants or natural products were reviewed [50–53]. These techniques are also suitable for phytochemical analysis of herbal tea, and their applications are summarized in Tables 3–5. 2.1. Conventional methods

Fig. 1. Sun Si-miao, a famous TCM doctor, proposed the concept of TCM formula used like the form of tea, in his masterpiece Beiji Qian Jin Yao Fang (AD 652).

thousands of years in many countries [1–4]. In China, history of using herbal tea may as long as the usage of traditional Chinese medicines (TCMs), and many TCMs are also consumed in the form of tea. At least in the Tang dynasty (AD 618–907), the concept of TCM formula used like the form of tea was proposed by a famous TCM doctor Sun Si-miao (AD 581–682) in his masterpiece Beiji Qian Jin Yao Fang (AD 652, Fig. 1). According to Shi Liao Ben Cao by Meng Shen (AD 621–713), the first monograph recorded the food with therapeutic effects in China, “to improve sexuality, decoct Gouqi (Lycium chinense Miller) and drink the soup as tea”. Nowadays in China, the plant species commonly used as herbal tea may derived from, (1) medicine and food dual purposes plants [5], (2) dietary supplement health food plants [6], and (3) traditional used non-Camellia plants with a history of more than hundreds years (Table 1). Generally, herbal tea has multiple beneficial effects, such as antioxidant, anti-inflammatory, antimicrobial, anti-carcinogenic, anti-atherogenic, anti-aging, cardioprotective, chemopreventive, hepatoprotective and neuroprotective activities [1,2,4,45,46], and can be used for promoting human health and reducing the risk of chronic diseases. These, together with the properties of attractive flavors, make herbal tea become popular

For analysis purposes, selection of solvents and extraction methods are critical to extract the compounds of interest. Because herbal tea is brewing beverage, classical methods such as decoction [54–57] and infusion (which is also named as maceration or soaking) [25,58–62] using water as solvent are effective extraction approaches for the extraction of saccharides, amino acids and other high-polar active ingredients. Occasionally, water solutions with additives (salts and acids, etc.) can be used to improve the extraction selectivity of acidic or basic ingredients, such as ascorbic acid, polyphenols, and alkaloids [58]. Extractions of high-polar compounds from herbal tea using water as solvent were also reported by shaking [63] and reflux extraction (RE) [12,39,64]. As for the extraction of volatile components such as essential oils and terpenes, water is also used as solvent at elevated temperature by the methods of hydro distillation (HD) [37,38,55,65–69] and steam distillation (SD) [38,70,71]. In order to extract moderate or low-polar active ingredients such as flavonoids, iridoids and saponins, different percentage of organic solvents (methanol, ethanol, acetone, etc.) in water or pure organic solvents are frequently used. Several conventional methods including infusion [24,72–80], vortex [36,37,74], shaking [32,81–88], RE [26,38,44,71,78,89–100], and Soxhlet extraction (SE) [74,78,95,101–109] have been used extensively for the extraction of various types of active components in herbal tea. All of these conventional methods are simple and easy to manipulate. Among them, RE and SE are the most classical solvent extraction techniques for the isolation and enrichment of analytes with low volatility and high thermal stability, and they allow a high recovery. HD and SD are the classical methods for discovery of volatile components from natural plants. It should be noted that these conventional methods have a number of shortcomings although they are now still in common use. RE and SE have the disadvantages of long extraction time, low extraction efficiency, and large consumption of solvents, cooling water and electric energy [53]. Both HD and SD are unable to extract water-soluble components, and an elevated temperature of 100 ◦ C may cause thermal decomposition of some substances. Thus, the development of novel sample pretreatment techniques with significant advantages, such as reduction in organic solvent consumption, elimination of additional sample clean-up and concentration steps before chromatographic analysis, improvement in

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J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Table 1 The list of herbal tea raw plants commonly used in China. No.

Chinese name

Common name

Medicine and food dual purposes plants Bai He Lily bulb 1

Origin (botanical name)

Used part

Processing

Ref.

Lilium lancifolium/L. brownii var. viridulum/L. pumilum Imperata cylindrica var. major Mentha haplocalyx/M. piperita/M. spicata Citrus reticulata, and its cultivated variants Citrus aurantium var. amara Lophatherum gracile Glycyrrhiza uralensis/G. inflata/G. glabra Lycium barbarum Nelumbo nucifera Ziziphus jujuba Sophora japonica

Scale leaf

Honey processing

[5,6]

Rhizome Aerial part

–a –

[5,6] [5,6]

Pericarp

Steaming

[5,6]

Flower bud Leaf and stem Root and rhizome

[5,6] [5,6] [5,6]

Fruit Leaf Fruit Flower bud

– – Roasting, honey processing – – Roasting Roasting

Cannabis sativa Agastache Rugosa Platycodon grandiflorum

Seed Aerial parts Root

Roasting – Roasting

[5,6] [5,6] [5,6]

Lonicera japonica Chrysanthemum morifolium Cassia obtusifolia Dimocarpus longan Phragmites communis Siraitia grosvenorii

Bud and flower Flower Seed Aril Rhizome Fruit

Roasting Roasting, steaming Roasting – – –

[5,6] [5,6] [5,6] [5,6] [5,6] [5,6]

Sterculia lychnophora Taraxacum mongolicum/T. borealisinense Lonicera macranthoides/L. hypoglauca/L. confusa/L. fulvotomentosa Morus alba

Seed Herb

– –

[5,6] [5,6]

Bud and flower

Roasting

[5,6]

Leaf

[5,6]

Fruit

Roasting, steaming, honey processing Roasting

Rhizome Seed Fruit

[5,6] [5,6] [5,6]

2 3

Bai Mao Gen Bo He

Lalang grass rhizome Peppermint/mint

4

Chen Pi

Tangerine peel

5 6 7

Dai Dai Hua Dan Zhu Ye Gan Cao

Bitter orange flower Common lophatherum Liquorice/licorice root

8 9 10 11

Gou Qi Zi He Ye Hong Zao Huai Mi

12 13 14

Huo Ma Ren Huo xiang Jie Geng

15 16 17 18 19 20

Jin Yin Hua Ju Hua Jue Ming Zi Long Yan Rou Lu Gen Luo Han Guo

21 22

Pang Da Hai Pu Gong Ying

Barbary wolfberry fruit Lotus leaf Chinese date/jujube/red date Japanese pagodatree flower-bud/Sophora flower bud Hemp seed/fructus cannabis Wrinkled giant hyssop Platycodon root/balloon flower/Chinese bellflower Honeysuckle flower Chrysanthemum Cassia seed Dried longan pulp/langan aril Reed rhizome Grosvenor momordica fruit/arhat fruit/buddha fruit Malva nut Dandelion herb

23

Shan Yin Hua

Wild honeysuckle flower

24

Sang Ye

Mulberry leaf

25

Shan Zha

Hawthorn fruit

26 27 28

Sheng Jiang Suan Zao Ren Wu Mei

Ginger Spina date seed Smoked plum/dark plum

Crataegus pinnatifida var. major/C. pinnatifida Zingiber officinale Ziziphus jujuba var. spinosa Prunus mume

29 30

Yu Xing Cao Yu Zhu

Heartleaf/houttuynia herb Fragrant solomonseal rhizome

Houttuynia cordata Polygonatum odoratum

Herb and aerial part Rhizome

31 32

Yi Yi Ren Zhi Zi

Coix seed/adlay Cape jasmine fruit

Coix lacryma-jobi var. ma-yuen Gardenia jasminoides

Seed Fruit

33

Zi Su

Perilla leaf/shiso leaf

Perilla frutescens

Leaf and stem

Roasting Roasting Vinegar processing, salt curing – Honey processing, steaming – Roasting, ginger processing –

Angelica sinensis Eucommia ulmoides Rhodiola crenulata

Root Leaf Rhizome and root

– Steaming –

[6] [6] [6]

Astragalus membranaceus var. mongholicus/A. membranaceus Centella asiatica Gynostemma pentaphyllum Ilex kudingcha/I. latifolia Aloe barbadensis Apocynum Venetum Ophiopogon japonicus Rosa rugosa Hibiscus sabdariffa Arctium lappa

Root

–

[6]

Aerial part Leaf and stem Leaf Leaf Leaf Root Flower Flower Root

– – Roasting, steaming Smashing Steaming – – – –

[6] [6] [6] [6] [6] [6] [6] [6] [6]

Citrus reticulata, and its cultivated variants Panax ginseng Panax ginseng Panax notoginseng Dendrobium nobile/D. chrysotoxum/D. fimbriatum Schisandra chinensis

Pericarp

Vinegar processing

[6]

Root Leaf Root Stem

Steaming – Steaming, frying Roasting

[6] [6] [6] [6]

Fruit

Vinegar processing, steaming

[6]

Dietary supplement health food plants 34 Dang Gui Chinese angelica 35 Du Zhong Ye Eucommia leaf 36 Hong Jing Tian Golden root/rose root/arctic root/lignum rhodium/Rhodiola rosea 37 Huang Qi Astragalus root/milkvetch root 38 39 40 41 42 43 44 45 46

Ji Xue Cao Jiao Gu Lan Ku Ding Lu Hui Luo Bu Ma Mai Dong Mei Gui Hua Mei Gui Qie Niu Bang Gen

47

Qing Pi

Centella Gynostemma pentaphyllum Kudingcha Aloe Dogbane leaf Dwarf lilyturf tuber Rose flower Roselle calyx Greater burdock/edible burdock/lappa Immature tangerine peel

48 49 50 51

Ren Shen Ren Shen Ye San Qi Shi Hu

Gingseng Gingseng leaf Radix notoginseng Dendrobium nobile

52

Wu Wei Zi

Schisandra fruit

[5,6] [5,6] [5,6] [5,6]

[5,6]

[5,6] [5,6] [5,6] [5,6] [5,6]

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Table 1 (Continued) No. 53 54 55 56 57

Chinese name

Common name

Origin (botanical name)

Used part

Processing

Ref.

Xi Yang Shen Ye Ju Hua Yi Mu Cao Yin Xing Ye Ze Lan

American ginseng Wild chrysanthemum Motherwort herb Ginkgo leaf Hirsute shiny bugleweed herb

Panax quinquefolius Chrysanthemum indicum Leonurus japonicus Ginkgo biloba Lycopus lucidus var. hirtus

Root Flower Aerial part Leaf Aerial part

Steaming – – Roasting, steaming –

[6] [6] [6] [6] [6]

Thamnolia vermicularis/T. subuliforms Hordeum vulgare Rabdosia rubescens Lithocarpus litseifolius (L. polystachyus) Lycium chinense/L. barbarum Rubus suavissimus Malus hupehensis Pistacia chinensis Scutellaria baicalensis/S. scordifolia/S. amoena/S.viscidula Sarcandra glabra Berchemia kulingensis Tussilago farfara Litsea coreana var. lanuginosa Forsythia suspensa Citrus limonia Semnostachya menglaensis Cyclocarya paliurus Malus sieboldi Mallotus furetianus Ilex hainanensis Chimonanthus nitens/Ch. salicifolius/Ch. zhejiangensis

Lichen

Roasting, steaming

[7]

Fruit Leaf or aerial part Leaf

Roasting Roasting, steaming Roasting, steaming

[8] [9] [10]

Leaf Leaf Leaf Leaf Aerial part

[11] [12] [13] [14] [15]

Twig and leaf Leaf Flower bud Leaf Leaf Fruit Leaf Leaf Leaf Leaf Leaf Leaf

Roasting, steaming Roasting, steaming Roasting, steaming Roasting, steaming Steaming, alcohol processing – – Honey processing Roasting, steaming Roasting, steaming – Roasting, steaming Roasting, steaming Roasting, steaming Roasting, steaming Roasting, steaming Roasting, steaming

Traditional used plants Bai Xue Cha 58 59 60 61

Da Mai Dong Ling Cao Duo Sui Ke

Vermiculate thamnolia thallus/snow tea Barley Rabdosia rubescens Lithocarpus litseifolius

62 63 64 65 66

Gou Qi Ye Guang Xi Tian Cha Hu Bei Hai Tang Huang Lian Mu Huang Qin

Barbary wolfberry leaf Sweet tea Malus hupehensis Chinese pistache Baical skullcap leaf

67 68 69 70 71 72 73 74 75 76 77 78

Sarcandra Berchemia kulingensis Common coltsfoot flower Hawk tea/eagle tea Forsythia suspense leaf Lemon Semnostachya menglaensis Cyclocarya paliurus Malus sieboldii Mallotus oblongifolius Hainan holly leaf Chimonanthus nitens

81 82

Jie Gu Cha Jiu Shan Teng Kuan Dong Hua Lao Ying Cha Lian Qiao Ye Ning Meng Nuo Mi Xiang Qing Qian Liu San Ye Hai Tang Shan Ku Cha Shan Lv Cha Shi Liang Cha/Shan La Mei Cha Shi Ya Cha Teng Cha/Duan Wu Cha Tian Ye Ju Xi Huang Cao

83 84

Xiang Si Teng Xiao Ye Ku Ding

Yine abrus Small-leaved kudingcha

85

Hong Xue Cha

Snow tea

79 80

a

[16] [17] [18,19] [20,21] [22] [23] [24] [25,26] [27] [28] [29,30] [31]

Adinandra nitida/cliff tea Vine tea

Adinandra nitida Ampelopsis grossedentata

Leaf Leaf, stem

Roasting, steaming Roasting, steaming

[32,33] [34]

Stevia rebaudiana Serrate rabdosia herb

Stevia rebaudiana Isodon serra/I. lophanthoides/I. lophanthoides var. gerardianus/I. lophanthoides var.graciliflorus Abrus precatorius Ligustrum robustum (syn. L. purpurascens) Lethariella cladonioides/L. zahlbruckneria/L. cashmeriana/L. sernanderi

Leaf Leaf or aerial part

Roasting, steaming –

[35–39] [40,41]

Leaf, stem Leaf

Roasting, steaming Roasting, steaming

[42] [43]

Lichen

Roasting, steaming

[44]

No special processing.

extraction efficiency and selectivity, is likely to play an important role.

2.2. Ultrasonic extraction Ultrasonic extraction (UE), ultrasonic-assisted extraction (UAE) or sonication, is a common extraction technique. UE is performed by means of ultrasonic vibration (frequencies from 16 kHz to 1 GHz), which is a source of energy facilitating the release of analytes from sample matrices. The improvement in extraction efficiency of UE owning to ultrasound appears at certain values of so-called acoustic pressure. Among the most important phenomena taking place in the acoustic field are cavitation (generation and collapse of mostly empty cavities), friction at the boundary and interfacial surfaces, and increase in the diffusion rate [53]. UE is the most widely used extraction technique in herbal tea analysis, and there are many reports regarding to its applications in the extraction of herbal tea raw plants [9,19,20,29,30,35,40,61,69,71,95,110–143]. In some cases, infusion is used before UE to enhance the extraction efficiency [43,109,144–149]. The extraction time of UE typically ranges from 10 min to 60 min for each time (Tables 3–5), which is much shorter

than that of SE, while the recoveries obtained by UE are comparable to those obtained by SE. Another advantage of UE is the possibility of extraction of many samples at the same time in an ultrasonic bath. Moreover, UE is usually carried out at room temperature, which makes it suitable for the extraction of thermally labile compounds.

2.3. Microwave-assisted extraction Microwave-assisted extraction (MAE) is a speedy, efficiency and solvent-saving extraction technique, which is based on the absorption of microwave energy by polar molecules of solvents and achieved an elevated temperature of 150–190 ◦ C [53], and the hot solvent allows the rapid partition of thermally stable compounds from sample matrices to solvent [150]. Several reviews showed that MAE has been continued used for the extraction of active components from natural products since its invention [50–53]. Researches regarding to the extraction of phytochemicals from herbal tea by using MAE were also reported [18,78,101,104,151–153]. Ginsenosides in Panax ginseng [101,152] and P. quinquefolius [104], polysaccharides in Cyclocarya paliurus [154], were all successfully isolated from matrices by using MAE. Moreover, trace toxic

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compounds such as pyrrolizidine alkaloids in Tussilago farfara [18] were also effectively extracted from herbal tea raw plant under optimized MAE conditions. In addition, ion liquids were also used to improve extraction efficiency, e.g., using 1-alkyl3-methylimidazolium-type ion liquid as solvent, the extraction efficiency of 3 phenolic alkaloids (liensinine, isoliensinine and neferine) in Nelumbo nucifera was 20–50% enhanced when compared with the regular MAE process under the same extraction conditions [151]. 2.4. Pressurized liquid extraction Pressurized liquid extraction (PLE) is a novel developed extraction technique which uses solvents to extract solid/semisolid samples under elevated temperature (50–200 ◦ C) and pressure (500–3000 psi) for short time periods (5–10 min) [155], it is also named as pressure solvent extraction (PSE), accelerated solvent extraction (ASE), and pressurized fluid extraction (PFE). Nowadays, PLE has been widely applied to extract active ingredients from herbal tea [18,21,55,95,156–160]. With regard to the extraction of the phytochemicals in herbal tea, PLE shows its remarkable advantage of high speed, e.g., 5 min is enough for extraction of flavonoids from licorice [157], gingerol and shogaol from ginger [95], and flavonoids, catechins, chlorogenic acid and epicatechin from Eagle tea [21]. Flavonoid, saponins, and polyacetylenes in P. ginseng were also successful extracted by PLE in 15 min [158]. Compared with other solvent extraction techniques, PLE shows more efficient with shorter extraction time and less extraction solvent. Hu et al. [95] compared the extraction efficiency of PLE, RE, SE, and UE, respectively, on gingerols and shogaol from ginger, which indicated that PLE had the advantages of shortest operation time, lowest solvent consumption and highest extraction efficiency. Similar results were also obtained based on the extraction of Z-ligustilide, Zbutylidenephthalide and ferulic acid from Angelica sinensis using PLE, UE and SE [161]. For most analytes, 5 min of PLE static extraction achieves almost comparable recoveries of 8 h RE/SE extraction. Further more, PLE showed better repeatability than other extraction methods due to high automation that reduces human handling error [162]. Special attention should be given to the fact that the thermal degradation might be occur in PLE process [5]. In spite of this, PLE is still an excellent choice for high efficiency extraction of phytochemicals from herbal tea. 2.5. Supercritical fluid extraction Supercritical fluid extraction (SFE) is an environmental friendly extraction method which by using supercritical fluids as media to achieve efficient extraction of the analytes from matrices. Possessing the properties of high diffusion coefficients and low viscosity, supercritical fluids penetrate samples almost as well as gases while their dissolving of analytes is similar to liquids, which results in the high extraction efficiency of SFE. The most commonly used extracting agent of SFE is CO2 , it possesses the advantages of low cost, low toxicity, and favorable critical parameters (Tc = 31.1 ◦ C, Pc = 74.8 atm). SFE has been used for many years for the extraction of volatile components, e.g., essential oils, fatty acids, and aroma compounds from plant materials, in both laboratory and industrial scale [52]. In the field of herbal tea analysis, SFE is seldom used [67,103]. As a non-polar extracting agent, CO2 is capable of dissolving non-polar or moderately polar compounds with high efficiency. While for the extraction of polar substances, a mixture of CO2 with modifiers (polar organic solvents) is used [55]. The modifiers increase the solubility of analytes, preventing them from adsorption on the active sites of sample matrix. Other advantages of SFE include the ability to perform rapid extractions, to reduce the

use of hazardous solvents, and to couple the extraction step with gas, liquid, or supercritical-fluid chromatography analysis. 2.6. Solid phase microextraction Solid phase microextraction (SPME) is a novel sample preparation technique developed in 1990s by Arthur and Pawliszyn of university of Waterloo [163]. SPME is a solvent-free sample preparation technique in which a fused silica fiber coated with polymer is introduced into the sample or the headspace above the sample, the targeted analytes are extracted and concentrated in the coating and then transferred to an analytical instrument for desorption and analysis [163–165]. SPME has been widely used in the fields of environment, food, natural products, pharmacy, and medicolegal expertise. Indeed, there are many researches focused on the extraction of volatile bioactive components from herbal tea raw plants by using SPME [41,67,166,167]. Actually, headspace (HS)–SPME were used in all of these applications because it provided higher efficiency than routine SPME for the extraction of volatile compounds. Huang et al. [67] illustrated the analysis of volatile compounds from Perilla frutescens by comparison of HS–SPME with HD and SFE. The chromatograms obtained from Baisu (a species of P. frutescens) after HS–SPME extraction were significantly different from those after HD and SFE extraction. Among the three extraction methods, HS–SPME is the simplest, most sensitive, and fastest method to analyze the fragrant components in the plant. The combination of MAE and HS–SPME is a very efficient approach for the extraction of volatile compounds from herbal tea raw plants. Deng et al. [168] developed a MAE followed by HS–SPME method for the extraction of camphor and borneol in Chrysanthemum indicum, and the method possessed the advantages of simple, rapid, organic solventfree and reliable for quantitative determination. 2.7. Solid phase extraction Solid phase extraction (SPE) is a sample preparation technique which is used for the clean-up and enrichment of targeted phytochemicals in the analysis of herbal tea [35,84,85,122,169,170]. During the sample preparation, both classical and novel methods often result in non-selective co-extraction of relatively large amounts of undesirable compounds (e.g., chlorophylls, sterols, etc.), which can severely affect the following separation and determination of targeted components. SPE is used for the removing of these undesirable interfering compounds, enriching the interested analytes and therefore improve the sensitivity of subsequently instrumental analysis. Reversed-phase C18 cartridges [84,122] and polymer cartridges [35,85] are often used for clean-up in herbal tea analysis. It should be noted that SPE is used only when the procedure of clean-up or enrichment is necessary, and the usage of SPE is not suitable for the discovering of the unknown components because the compounds of interest might be lost during the washing step. 3. Effects of processing on components in herbal tea Like tea from leaves of C. sinensis, raw materials for herbal tea are sometimes should be processed in appropriate ways. Generally, the commonly used methods include: (1) heating such as steaming, roasting and baking, (2) adjuvant materials processing, and (3) biochemical treatment such as fermentation. Clearly, these processing may greatly influence the components in herbal tea (Table 2). 3.1. Heating Heating processing generally operated at high temperature (above 100 ◦ C) to cause variation and transformation of certain

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

7

Table 2 Variation of components in herbal tea during processings. Processing

Herbal tea plants

Variation of components

Ref.

Heating Roasting

Fruit of Gardenia jasminoides

Decreased: gardenoside (slightly), crocin (significantly) Decreased: ursolic acid Decreased: tea polyphenols, free amino acids

[171] [172] [173]

Decreased: protein, polyphenols, carbohydrates, flavonoids Increased: free amino acids Decreased: total phenols, total flavonoids

[174]

Increased: 2-methylpyrazine, 2,5-dimethylpyrazine, 2-acetyl-1-pyrroline. Variation in fingerprint profile Decreased: glycosides (rubrofusarin-6-O-␤-gentiobioside, rubrofusarin-6-O-␤-d-apiofuranosyl-(1,6)-O-␤-d-glucopyranside) Increased: free anthraquinones (emodin, chrysophanol, physcion) Variation in fingerprint profile Decreased: organic acid, tannin Decreased: tea polyphenols, flavonoids, free amino acids, soluble sugars, chlorophyll Decreased: 6-gingerol, 8-gingerol, 10-gingerol Increased: 6-shogaol Variation in fingerprint profile Decreased: volatile oil

[176]

Decreased: amino acids (dencichine, glutamic acid, serine, asparagine, glycine, glutamine, histidine, taurine, arginine, threonine, alanine, proline, tyrosine, valine, isoleucine, leucine, phenylalanine, tryptophan, lysine, ␥-aminobutyric acid) Decreased: saponins (ginsenoside Rg1 , Re, Rb1 , Rb2 , Rc and Rd) Increased: ginsenoside Rg3 Decreased: saponins (notoginsenoside R1 , ginsenoside Re, Rg1 , Rb1 , Rc, Rd). Variation in fingerprint profile Decreased: saponins (notoginsenoside R1 , ginsenoside Rg1 , Rb1 , Rd and Re) Increased: saponins (ginsenoside Rg3 , Rh1 , Rh2 , Rk3 , Rh4 , Rk1 and Rg5 ) Decreased: dencichine Decreased: saponins (notoginsenoside R1 , ginsenoside Rg1 , Rb1 , Rd and Re) Increased: saponins (20(S)-Rh1 , 20(R)-Rh1 , Rk3 , Rh4 , 20(S)-Rg3 , 20(R)-Rg3 , Rk1 and Rg5 ) Variation in fingerprint profile Decreased: saponins (ginsenoside Rg1 , Re, Rb1 , Rc, Rb2 , Rb3 , and Rd) Increased: saponins (ginsenoside Rh1 , Rg2 , 20(R)-Rg2 , Rg3 and Rh2 )

[183]

Decreased: 2,2-dimethyl-6-acetyl chromanone Increased: rutin; hyperoside; trans-ferulic acid; 4,5-O-dicaffeoylquinic acid; tussilagone; 7␤-(3 -ethylcrotonoyloxy)-1␣-(2 -methylbutyryloxy)-3,14dehydro-Z-notonipetranone Preserved: chlorogenic acid; trans-caffeic acid Increased after honey processing; 5-hydroxymethyl furfural Decreased after alcohol processing: 5-hydroxymethyl furfural Decreased: liquiritin apioside, licuraside Increased: liquiritin, isoliquirition. Increased: polysaccharides. Decreased after honey processing: flavonoids (calycosin-7-O-␤-d-glucoside, formononetin-7-O-␤-d-glucoside, calycosin, formononetin) Decreased after alcohol processing: calycosin Decreased: minerals (Na, Mg, K, Ca, Mn, Fe, Sr), organic acid (citric acid, tartaric acid and succinic acid) Increased: minerals (K, Cu, Ba), oxalic acid Perserved: malic acid Decreased: total polyphenols, amygdalin Decreased: lignans (schizandrin, aomisin, schisantherin A, deoxyschizandrin, ␥-schizandrin, schisandrin C) Increased: organic acids (quinic acid, citric acid, protocatechunic acid) Decreased: total flavonoids

[190]

Increased: ginsenoside Rh4

[199]

Roasting, steaming, microwave heating Roasting

Leaves of Apocynum Venetum Leaves of Eucommia ulmoides

Roasting, microwave heating, steaming, hot air heating Roasting

Root of Polygonatum odoratum

Roasting

Seed of Cassia obtusifolia

Steaming, wetting Steaming, blanching, microwave heating Steaming

Fruit of Prunus mume Leaves of Lycium barbarum

Steaming, heating in sealed vessel Steaming

Steaming

Rhizome of Zingiber officinale

Root of Panax ginseng

Root of Panax notoginseng

Steaming, baking

Steaming

Processing with adjuvant material Honey processing

Root of Panax quinquefolius

Flower bud of Tussilago farfara

Honey processing, alcohol processing Honey processing

Fruit of Schisandra chinensis Licorice root

Honey processing, alcohol processing

Lily bulb of Lilium lancifolium Root of Astragalus membranaceus

Salt cure

Fruit of Prunus mume

Vinegar processing

Fruit of Schisandra chinensis

Peel of immature Citrus reticulata Fermentation Fermentation with Bacillus subtilis

Root of Panax notoginseng

nutrients for different purposes. In traditional manufacturing of Chinese tea, moderately heating, Sha-qing in Chinese, is an important procedure for deactivating oxidative enzymes and removing unwanted scents in the leaves [200]. Similar processing could also be used for herbal tea, such as leaves of Eucommia ulmoides [175],

[175]

[177]

[178] [179] [180] [181]

[182]

[184] [185] [186] [187] [188]

[189] [184]

[191] [192] [193] [194]

[195]

[196] [197]

[198]

Lycium barbarum [180] and Apocynum Venetum [173]. Steaming [173,175,179–189] and roasting [171–178] are most commonly used for heating processing of herbal tea. Indeed, many types of chemical reactions, including hydrolysis, oxidation, isomerization and decomposition reactions may occur during heating

8

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

processing of herbs [201]. Heating can induce significant loss of ingredients, such as volatile components [181,182], amino acids [183,187], proteins [174], phenols [174], flavonoids [174], carbohydrates [174], glycosides [171,177,178,184–186,188,189], organic acids [172,179] and tannin [179] in herbal tea. The degradation of main saponins (notoginsenoside R1 , ginsenoside Rg1 , Re, Rb1 and Rd) in San Qi (root of Panax notoginseng) were found after steaming at above 100 ◦ C for 9–48 h. Hydrolysis or dehydration occurred in the sugar moieties attached to C-3, C-6 or C-20 of saponins’ structures yielded more new-formed saponins, including ginsenoside Rg3 , Rh1 , Rh2 , Rk3 , Rh4 , Rk1 , Rg5 , 20(S)-Rh1 , 20(R)-Rh1 , 20(S)-Rg3 and 20(R)-Rg3 [185,186,188]. The antiproliferative and radical scavenging activity may be enhanced according to compositional variation after heating processing [186], and the finding has led to use of processing for enhancement of ginsenosides’ biological activity [202]. Meanwhile, a thermally unstable amino acid dencichine (␤-ODAP) responsible to hemostatic activity of San Qi, was hydrolyzed after steaming at 100–120 ◦ C [183,186,203]. The compositional change could well explained the different traditional use of raw and steamed San Qi for hemostasis and ‘nourish’ blood as a tonic, respectively. Chemical profile of ginger (rhizome of Zingiber officinale) was significantly changed after steaming at 100–120 ◦ C, and the antiproliferative effect of steamed ginger at 120 ◦ C for 4 h was approximately 1.5- and 2-fold higher than that of dried and fresh ginger, respectively. The decreased concentration of gingerols (16.20, 13.90 and 6.34 mg/g in fresh, dried and steamed ginger, respectively) and increased levels of shogaols (0.40, 0.69 and 4.63 mg/g in fresh, dried and steamed ginger, respectively) contributed to the improved anticancer potential of the steamed ginger [181]. Similarly, during roasting of seed of Cassia obtusifolia, glycosides such as rubrofusarin-6-O-␤-gentiobioside were decomposed into free anthraquinones such as emodin, chrysophanol and physcion [177] and cause related chemical profile variation [178]. Therefore, heating temperature should be carefully optimized. For thermally sensitive volatile components, moderate temperature up to 60 ◦ C may cause notable loss [182]. In addition, in order to evaluate innate flavor during the roasting process, the components responsible for the aroma of unroasted Polygonatum odoratum root and the volatile odor components released during the roasting process were evaluated using HS–SPME method. The results showed that P. odoratum after roasting revealed a high concentration of 2,5-dimethylpyrazine at 130 ◦ C and 150 ◦ C, but a low concentration at 110 ◦ C. Most of the 2-acetyl-1-pyrroline, which significantly affected its smell, was revealed at 130 ◦ C [176].

3.2. Adjuvant materials processing Adjuvant materials processing has multiple effects on herbal tea. Salt curing is a conventional procedure for processing of dark plum (fruit of Prunus mume) in harvesting time, and the cured dark plum with high concentration of salt will be rinsed with water to adjust taste before use [195,196]. However, abundant nutrients such as minerals, organic acids, polyphenols and amygdalin were significantly decreased during the processing [196]. In addition, other commonly used adjuvant materials including honey, vinegar and alcohol. Besides, heating after mixing herbal and adjuvant materials is generally required. Content of 5-hydroxymethyl furfural (5-HMF) was found to be higher in honey processed schisandra fruit (Schisandra chinensis) than in raw material, which may attribute to the dehydration of carbohydrates in honey under heating [191]. Honey processing also induced sugar chain hydrolyzation of liquiritin apioside and licuraside in licorice root [192], while vinegar processing not only increased amount of organic acids directly, but also provided a weak acidic environment during heating and therefore improved isomerization of lignans in schisandra fruit [197].

Alcohol may accelerate decarboxylation of some flavonoids in root of Astragalus membranaceus and decreased their amount [194]. 3.3. Fermentation Using fermentation as a traditional processing for herbal medicine has more than one thousand years in China and it can be used for producing secondary metabolites, formation of new constituents, reducing toxicity and improving efficacy of herbs [204]. Ginsenoside Rh4 , an anti-tumor component, was greatly increased when P. notoginseng was fermented with Bacillus subtilis [199]. The possible pathway of ginsenoside Rh4 production may be the dehydration of ginsenoside Rh1 or loss of sugar moiety of ginsenoside Re. 4. Phytochemical analysis 4.1. Gas chromatography and hyphenated techniques Gas chromatography (GC) and hyphenated techniques are of the powerful tools for the detection of volatile compounds or non-volatile compounds readily derivatized with high sensitivity. In the past few years, GC and hyphenated techniques have been widely used in the analysis of herbal tea. The fused-silica capillary column is the most common used. As for the oven temperature control mode, temperature programming is used for nearly all of the analysis because herbal tea contains complex components with different boiling points. Flame ionization detector (FID) is widely used for detection because it is a universal detector possessing advantages of simplicity, cheapness, sensitivity, and wide range of linear response, although this technique has been in the use for over 50 years since its invention. Other conventional detector such as electron capture detector (ECD), nitrogen phosphorus detector (NPD), and flame photometric detector (FPD) are seldom used in herbal tea analysis because their are optional detectors for the elements of halogens, nitrogen, phosphorus, and sulfur, while many volatile components in herbal tea do not contain these elements. It should be noted that GC coupled with mass spectrometry (GC–MS) provides predominant abilities for both qualitative and quantitative analysis of volatile compounds in herbal tea because MS possesses the abilities of providing structural information and highselectivity for each compound by selective ion monitoring (SIM) and/or multiple reaction monitoring (MRM). And more than 90% of one-dimensional GC–MS methods in herbal tea analysis employ quadrupole mass analyzer. GC has been recognized as a tool offering higher peak capacities than other chromatographic techniques [205]. Usually, onedimensional GC on capillary columns can separate 100–150 peaks in one run. In spite of that, the peak capacity does not suffice to separate the individual constituents in many cases of phytochemical analysis. One way to overcome the difficulty is the usage of comprehensive two-dimensional gas chromatography (GC × GC) system, which is performed by coupling two GC columns with distinctly different separation mechanisms together and allowing continuous heart-cuts from the first column to be analyzed on the second column by using a modulator [205,206]. Undoubtedly, the introduction of GC × GC is the most important development of GC analysis in recent years. The peak capacity of a GC × GC system is of the multiplication of two columns rather than the addition, which can even reaches 6000–9000. Thus, GC × GC is especially suitable for the analysis of very complex mixture, offering unsurpassed separation resolution and detection sensitivity. In last decade, GC × GC has been widely used in the fields of petrochemical, food, environment, and natural products [207,208], and this technique has also been introduced to analyze volatile bioactive components

Table 3 Applications of GC and hyphenated techniques in the phytochemical analysis of herbal teas. Analytes GC, GC–MS Acids, sugars, sugar alcohols (TMS derivatives) Camphor, borneol

Essential oils

Sample preparation

Column

Separation conditions

Detection

Ref.

Crataegus spp.

UE: water, 30 min

Supelco simplicity-1, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 150–275 ◦ C

FID

[29]

Chrysanthemum indicum

MAE followed by SPME: MAE, water, 400 W, irradiation time: 4 min; HS–SPME, fiber of PDMS/DVB, 40 ◦ C, 20 min, stirring rate of 1100 rpm RE: ethyl acetate, 80 ◦ C, 4 h; SD: water, 6 h; UE: ethyl acetate, 25 ◦ C, 20 min SE: chloroform, 5 h, SE residue with menthanol, 5 h. HD: water, 4 h

HP-5MS, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 40–300 ◦ C

Q–MS: EI

[168]

DB-5MS, 30 m × 0.25 mm, ␮m

Temperature programming, 50–280 ◦ C

Q–MS: EI

[71]

OV-1, 30 m × 0.25 mm, 0.25 ␮m HP-5MS, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 60–280 C Temperature programming, 70–220 ◦ C

FID; Q–MS: EI FID; Q–MS: EI

[109] [68]

HD: water, 3 h HD: distilled water, 3 h

Rtx-5MS, 30 m × 0.25 mm, 0.25 ␮m OV-1, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 60–250 ◦ C Temperature programming, 65–260 ◦ C

Q–MS: EI Q–MS: EI

[66] [65]

HD: water, 5 h HD: water, 3 h; SD: water, 3 h RE: n-hexane with 5% sodium bicarbonate solution

DB-5, 30 m × 0.25 mm, 0.25 ␮m VF-5, 30 m × 0.25 mm, 0.25 ␮m BP-50

FID; Q–MS: EI Q–MS: EI FID

[37] [38] [38]

CP-SIL 88 CB FAME, 50 m × 0.25 mm, 0.2 ␮m

FID

[98]

Ziziphus jujuba

RE: methylation mixture (MeOH: benzene:2,2dimethoxypropane:H2 SO4 = 39:20:5:2)–heptane (17:10, v/v) 80 ◦ C, 2 h SE: chloroform–methanol (2:1, v/v)

Temperature programming, 35–250 ◦ C Temperature programming, 50–300 ◦ C Temperature programming, 170–270 ◦ C Temperature programming, 110–210 ◦ C

CP-Wax 52 CB, 50 m × 0.32 mm, 1.2 ␮m

Temperature programming, 60–240 ◦ C

Q–MS: EI

[74]

Citrus aurantium var. amara Eucommia ulmoides Mentha haplocalyx Mentha spicata Nelumbo nucifera Pericarpium Citri Reticulatae Viride, Pericarpium Citri Reticulatae Stevia rebaudiana Stevia rebaudiana Coix lacryma-jobi var. ma-yuen

◦

Fatty acid methyl esters Fingerprint (petroleum ether extract) Growth inhibitors

Tussilago farfara

UE: petroleum ether, 1 h

DB-5MS, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 60–280 ◦ C

IT–MS: EI

[19]

Imperata cylindrica

Shaking extraction: 70% methanol, 25 ◦ C, 24 h

DB-5MS, 30 m × 0.25 mm, 0.25 ␮m

Q–MS: EI

[87]

Metabolite profile

Aloe barbadensis

Shaking extraction: methanol, 12 h; oximated with methoxyamine hydrochloride; derivatizated with MSTFA HD: water, 6 h Shaking extraction: deionized water (1:10, w/v), 100 ◦ C, 30 min

VF-1MS, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 100–280 ◦ C Temperature programming, 100–300 ◦ C

IT–MS: EI

[88]

DB-5MS, 30 m × 0.25 mm, 0.25 ␮m HP-5MS, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 80–280 ◦ C Temperature programming, 150–270 ◦ C

Q–MS: EI FID

[69] [63]

Infusion: ultra-pure water, 80 ◦ C, 2 h × 2 times UE: diethylether, 4 ◦ C, 30 min for perilla ketone Shaking extraction:1% ascorbic acid in ethanol (w/v), 80 ◦ C, 10 min, then add 44% KOH for saponification, 80 ◦ C, 18 min, cool in ice bucket, add 50% n-hexane, centrifugation, collect n-hexane layer. Process 3 times. Wash n-hexane layer with water, passed through anhydrous Na2 SO4 , concentration and dissolve in isooctane SE: n-hexane, 20 h; 96% SE: ethanol, 20 h; SFE: CO2 , 40 ◦ C, 30 min static and 30/60 min dynamic extraction HS–SPME: fiber of CAR-PDMS, 60 min, ionic strength of 0.08 g mL−1 NaCl solution HS–SPME: fiber of DVB–CAR–PDMS, 40 ◦ C, 20 min

DB-1701, 30 m × 0.32 mm, 0.25 ␮m Supelcowax-10, 60 m × 0.25 mm, 0.25 ␮m CP-SIL 8CB, 30 m × 0.25 mm, 0.4 ␮m

Temperature programming, 70–250 ◦ C Temperature programming, 50–240 ◦ C Temperature programming, 220–310 ◦ C

FID Q–MS: EI FID

[25] [125] [98]

DB-5MS, 25 m × 0.2 mm, 0.33 ␮m; HP-5MS, 30 m × 0.25 mm, 0.25 ␮m

Temperature programming, 120–310 ◦ C; temperature programming, 140–300 ◦ C Temperature programming, 60–240 ◦ C

FID; Q–MS: EI

[103]

Q–MS: EI

[166]

Temperature programming, 35–240 C

Q–MS: EI

[167]

Temperature programming, 40–250 ◦ C Temperature programming, 50–300 ◦ C

Q–MS: EI Q–MS: EI

[41] [67]

Monosaccharide (hydrolysates of polysaccharide)

Schisandra chinensis Lycium barbarum

Perilla ketone Squalene, phytosterols

Cyclocarya paliurus Perilla frutescens Coix lacryma-jobi var. ma-yuen

Triterpenes

Morus alba

Volatile compounds

Dimocarpus longan

Isodon serra Perilla frutescens

HS–SPME: fiber of CAR/PDMS, 50 ◦ C for 40 min HD: water, 6 h; SFE: CO2 , 30 MPa, 45 ◦ C, 60 min; HS–SPME: fiber of CAR/PDMS, 45 ◦ C, 20 min

HP-VOC, 60 m × 0.32 mm, 1.8 ␮m DB-WAX, 30 m × 25 mm, 25 ␮m; HP–5MS, 30 m × 25 mm, 25 ␮m TR-5MS, 30 m × 0.25 mm, 0.25 ␮m Capillary column 30 m × 0.25 mm, 0.25 ␮m

◦

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Fatty acids

Herbal tea plants

9

EI, electron impact; FID, flame ionization detection; GC, gas chromatography; GC × GC, comprehensive two-dimensional gas chromatography; MS, mass spectrometry; Q, quadrupole; TOF, time-of-flight.

[70] TOF–MS: EI SD: water Mentha haplocalyx Ketones, terpenes

Temperature programming, 70–260 ◦ C

[23] FID Temperature programming, 50–280 ◦ C Dilute 1:10 (v/v) in n-hexane Citrus essential oil

Supelcowax-10, 30 m × 0.25 mm, 0.25 ␮m; SPB-5, 1 m ×0.10 mm, 0.10 ␮m DB-XLB, 30 m × 0.25 mm, 0.25 ␮m; BPX-50, 1 m × 0.1 mm, 0.1 ␮m

[145] TOF–MS: EI Temperature programming, 70–270 ◦ C DB5, 20 m × 0.25 mm, 0.5 ␮m; Rtx200, 2 m × 0.18 mm, 0.2 ␮m Infusion followed by UE: chloroform–methanol–water (1:3:1, v/v/v), infusion: 1 h, UE: 10 min Ocimum basilicum, Mentha piperita, Stevia rebaudiana

Q–MS: EI Temperature programming, 60–250 ◦ C SPB-1, 30 m × 0.25 mm, 1 ␮m Semnostachya menglaensis

GC × GC, GC × GC–MS Carboxylic acids, carbohydrates, amino acids (TMS derivatives) Essential oils

Q–MS: EI FID; Q–MS: EI Temperature programming, 40–280 ◦ C Temperature programming, 40–250 ◦ C

[24]

Detection Separation conditions

DB-5MS, 30 m × 0.25 mm, 0.25 ␮m Capillary column 30 m × 0.25 mm, 0.25 ␮m

Inusion: dichloromethane MAE: ionic liquid ([C12mim] Br), 385 W, 40 min × 3 times; Inusion: hexane Schisandra chinensis

Column Sample preparation Herbal tea plants Analytes

Table 3 (Continued)

[80] [153]

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Ref.

10

in herbal tea [23]. When GC × GC is coupled with a mass spectrometer, the hyphenated technique becomes a very powerful tool for the discovery of unknown bioactive components from natural plants, especially when a high resolution time-of-flight (TOF) mass spectrometer is used. GC × GC–MS has also been used for the analysis of herbal tea [70,145]. Cao et al. [70] illustrated the analysis of volatile components for fresh Mentha haplocalyx by using GC × GC–TOF-MS. Using a non-polar column as the first dimension and a middle-polar column as the second dimension, 163 ketones and terpenes were completely separated and identified, while less than 50 components were identified in this raw plant using conventional GC–MS [68]. Unfortunately, the applications of GC × GC–TOF-MS in the analysis of herbal tea are very limited, and these should be improved in the future. Another significant application of GC and hyphenated technique in phytochemical analysis of herbal tea is the determination of water-soluable components such as saccharides, amino acids, and other polar active ingredients. Because herbal tea is drinked as water extracts, the analysis of water-soluable saccharides is crucial for their quality control. The analysis can be achieved by GC and hyphenated techniques via derivatization and/or hydrolysis. Sugars and sugar alcohols in three species of hawthorn (Crataegus spp.) were derivatized by trimethylsilyl (TMS) and analyzed by GC–FID and GC–MS [29]; water-soluble polysaccharides in L. barbarum [63] and C. paliurus [25] were hydrolyzed, and their hydrolysates (i.e., monosaccharide) were successful analyzed by GC–FID. TMS-derivatized carbohydrates from Mentha piperita and Stevia rebaudiana were also analyzed by GC × GC–TOF-MS [145]. The typical applications of GC in herbal tea analysis are summarized in Table 3. 4.2. Liquid chromatography and hyphenated techniques 4.2.1. Separation 4.2.1.1. High performance liquid chromatography. High performance liquid chromatography (HPLC) is a routine and popular method for phytochemical analysis because it possesses the outstanding advantages of good repeatability, wide applicability, and reasonable qualitative and quantitative capability. HPLC, especially reversed-phase HPLC (RP-HPLC), and hyphenated techniques are the most widely used for the analysis of herbal tea. Besides octadecylsilane bonded silica gel (C18 ), C30 [83,125] is also used in some cases. RP-HPLC was also used for the analysis of monosaccharide using pre-column derivatization approach. The derivatives of mannose, ribose, rhamnose, glucuronic acid, galacturonic acid, glucose, xylose, galactose, arabinose and fucose were baseline separated on a RP-C18 column within 40 min using 1-phenyl-3-methyl-5pyrazolone as derivatization reagent [60]. Normal-phase HPLC (using cyano-, amino-, and diol-bonded silica gel as adsorbents) is seldom used in herbal tea analysis, although this technique is very suitable for the analysis of highly polar compounds whose retention on RP-HPLC is very weak. Both isocratic elution and gradient elution are widely used in herbal tea analysis. Isocratic elution was preferable for the determination of single or several targeted compounds [26,35,57,58,98,209]. However, isocratic elution is deficient for the separation of herbal tea extracts containing complex and unknown components, and gradient elution is used in these cases. In most of the analysis of herbal tea by RP-HPLC, gradient elution is used with the mobile phases of water and organic solvent of methanol/acetonitrile, and gradient elution is generally performed with organic solvent in the ranges of 5–100% because herbal tea contain a wide polarity of components. The usage of mobile phases with high concentrations of an organic solvent (up to 90–100%) is required because the extracts of herbal tea always contain fatsoluble components of interest or impurities.

Table 4 Applications of LC and hyphenated techniques in the phytochemical analysis of herbal teas. Herbal teas

Sample preparation

Column

Separation conditions

Detection

Ref.

HPLC, HPLC–MS 1-Deoxynojirimycin

Morus alba

UE: 70% methanol, 15 min × 3 times

[113]

Zingiber officinale

DAD: 230 nm; QTOF–MS: ESI (+)

[95]

␣-Tocopherol, ␤-carotene

Ziziphus jujuba

RE: ethanol, 85 ◦ C, 8 h; UE: ethanol, 25–30 ◦ C, 40 kHz, 1 h; PLE: 70% ethanol, 100 ◦ C, 1500 psi, static extraction time of 5 min, 1 cycle Vortex: hexane

Gradient elution with 0.1% formic acid and acetonitrile, 0.6 mL/min, 40 ◦ C Gradient elution with water and acetonitrile, 0.2 mL/min, 30 ◦ C

QqQ–MS: ESI (+)

6-Gingerol, 8-gingerol, 10-gingerol, 6-shogaol

TSKgel Amide-80, 250 mm × 4.6 mm, 5 ␮m Kinetex 150 mm × 3 mm, 2.6 ␮m

YMC-Pack ODS-AM 250 mm × 4.60 mm, 5 mm

DAD: 296, 450 nm

[74]

Anthraquinones

Cassia obtusifolia

RE: 95% ethanol, 1 h

UV: 278 nm

[43]

Antioxidants

Lonicera japonica

Infusion followed by UE: methanol, ethanol, water, and 70% methanol, respectively, infusion, 1 h UE, 40 min Infusion: boiling water, 10 mim; UE: 70% methanol, 15 min × 2 times MAE: 80% ethanol (1:25, w/v), 70 ◦ C, 5 min × 3 times; SE: 80% ethanol, 90 ◦ C, 4 h; RE: 80% ethanol, 90 ◦ C, 1 h × 3 times; UE: 80% ethanol, 40 min × 3 times, 100 W; infusion: 80% ethanol, 12 h Infusion: 80% ethanol, 8 h

Lunar C18 250 mm × 4.6 mm, 5 ␮m Zorbax Extend C18 , 250 mm × 4.6 mm, 5 ␮m

Isocratic elution with methanol–acetonitrile–tetrahydrofuran (73:20:7, v/v/v) 1 ml/min. Gradient elution with 0.1% aqueous phosphoric acid and acetonitrile, 1.0 mL/min Gradient elution with 0.4% acetic acid and acetonitrile, 1 mL/min, 35 ◦ C

DAD: 240, 360 nm; TOF–MS: ESI (−)

[146]

Gemini, 250 mm × 4.6 mm, 5 ␮m Eclipse XDB C18 , 150 mm × 4.6 mm, 5 ␮m

Gradient elution with 0.1% formic acid and methanol, 0.6 mL/min, 25 ◦ C Gradient elution with 0.05% formic acid and acetonitrile, 0.7 mL/min, 30 ◦ C

VIS: 515 nm; QqQ–MS: ESI (−) QqQ–MS: ESI (+)

[61]

VP-ODS C18 , 250 mm × 2 mm, 5 ␮m Polymeric C30 , 250 mm × 4.6 mm, 5 ␮m

UV: 280, 325 nm Q–MS: ESI (+) DAD: 450 nm; Q–MS: APCI (+)

[62]

Alltima C18 , 150 mm × 4.6 mm, 5 ␮m Shim-pack VP-ODS, 150 mm × 4.6 mm, 5 ␮m HyPURITY C18 , 150 mm × 4.6 mm, 5 ␮m

Gradient elution with water and methanol (both containing 0.1 formic acid), 1 mL/min Gradient elution with dichloromethane and methanol–acetonitrile–water (84:14:5, v/v/v), 1 mL/min, 25 ◦ C Gradient elution with 0.2% acetic acid and acetonitrile, 0.6 mL/min Isocratic elution with ethanol–water–acetic acid (24:75:1, v/v), 1 mL/min, 30 ◦ C Gradient elution with acetone, acetonitrile and methanol, 1 mL/min

DAD: 280 nm; MS: ESI (+) (−) UV: 240 nm

[117]

VIS: 660 nm; Q–MS: APCI (+)

[82]

Zorbax ODS C18 , 250 mm × 4.6 mm, 5 ␮m

Gradient elution with 1% acetic acid and acetonitrile, 1 mL/min, 25 ◦ C

DAD: 260, 324 nm

[55]

Zorbax XDB-C18 250 mm × 4.6 mm, 5 ␮m

Gradient elution with 2 mM ammonium acetate–0.01% acetic acid and acetonitrile, 1 mL/min, 30 ◦ C Gradient elution with water and methanol (both containing 0.1% formic acid), 0.7 mL/min, 25 ◦ C Gradient elution with 1.414 × 10−2 M phosphoric acid and acetonitrile–methanol (1:2, v/v), 1 mL/min Gradient elution with 0.5% acetic acid and acetonitrile, 1.2 mL/min, 25 ◦ C Isocratic elution with 0.5% phosphoric acid–methanol (1:1, v/v), 0.8 mL/min, 25 ◦ C

TOF–MS: ESI (+)

[54]

QTrap–MS: ESI (−)

[40]

DAD: 278 nm

[76]

DAD: 254 nm; IT–MS: ESI (+) UV: 360 nm

[94]

Houttuynia cordata Astragalosides

Astragalus membranaceus var. mongholicus

Caffeoylquinic acids, lignans Carotenoids

Arctium lappa

Chlorogenic acid, flavonoids Chlorogenic aid, geniposidic acid Chlorophylls and their derivatives

Lycium barbarum

Houttuynia cordata

Shaking extraction: hexane–ethanol–acetone–toluene (10:6:7:7, v/v/v/v), 1 h UE: 70% methanol, 30 min ◦

Coniferyl ferulate, ferulic acid, Z/E-ligustilide, Z/Ebutylidenephthalide

Angelica sinensis

Diarylheptanoids, gingerol-related compounds Diterpenoids, flavonoids, phenolic acids

Ginger

Decoction: distilled water, 60 C, 1 h × 2 times Shaking extraction: hexane–acetone–ethanol–toluene (10:7:6:7, v/v/v/v), 20 min UE: methanol–formic acid (95:5, v/v), 320 W, 40 min; PLE: methanol, 100 ◦ C, static extraction time of 10 min, 1200 psi, 2 static cycles; SFE: modifier of ethyl acetate, 350 bar, 50 ◦ C, static time of 4 h; HD: water, 6 h; decoction: water, 20 min Decoction: water, 90 min × 3 times

Isodon serra

UE: methanol, ice-water bath, 60 min

Diamonsil C18 , 250 mm × 4.6 mm, 5 ␮m

Flavonoid glycosides

Chrysanthemum morifolium

Infusion followed by RE: infusion, 70% ethanol, 14 h; RE, 70% ethanol, 2 h

Kromasil 100-5 C18 , 250 mm × 4.6 mm, 5 ␮m

Flavonoids

Apocynum venetum

RE: 50% ethanol

C18 , 250 mm × 4.6 mm, 5 ␮m

Eucommia ulmoides Gynostemma pentaphyllum

Cyclocarya paliurus

◦

RE: methanol–HCl (4:1, v/v), 100 C, 1 h for quercetin, kaempfero; 70% methanol, 80 ◦ C, 2 h for isoquercitrin

Kromsil C18 , 200 mm × 4.6 mm, 5 ␮m

[78]

[83]

[57]

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Analytes

[26]

11

12

Table 4 (Continued) Analytes

Herbal teas

Sample preparation

Column

Separation conditions

Detection

Ref.

Eucommia ulmoides

Degrease with petroleum ether, 80 ◦ C, 3 h, followed by infusion: 80% alcohol, 24 h, then UE: 80% alcohol, 1 h × 3 times RE: 95% ethanol at 90 ◦ C, 2 h

Spherisorb RP18, 250 mm × 4.6 mm, 5 ␮m

Gradient elution with 0.1% phosphoric acid and acetonitrile, 0.8 mL/min

UV: 362 nm

[109]

LunaTM , 250 mm × 4.6 mm, 5 ␮m Synergi Hydro C18 50 mm × 2.1 mm, 4 ␮m

Gradient elution with 1% acetic acid and acetonitrile Gradient elution with water and acetonitrile (containing 0.05% formic acid), 0.4 mL/min, 40 ◦ C Gradient elution with water and acetonitrile (both containing 0.1% formic acid) Gradient elution with 0.3% (v/v) acetic acid (pH adjusted to 4.0) and acetonitrile, 0.8 mL/min, 25 ◦ C Gradient elution with 0.08% acetic acid and acetonitrile, 1 mL/min, 25 ◦ C Gradient elution with water and acetonitrile (both containing 1% formic acid), 0.8 mL/min Gradient elution with water and acetonitrile (both containing 0.1% formic acid), 1 mL/min, 25 ◦ C Gradient elution with 0.1% formic acid (pH = 4.0) and acetonitrile, 0.2 mL/min Gradient elution with water and methanol, 1 mL/min

UV: 370 nm

[91]

QTOF–MS: ESI (+)

[91]

DAD: 370 nm

[105]

UV: 265 nm

[138]

DAD: 276 nm; IT–MS: ESI (+) (−) UV: 260 nm; QTrap–MS: ESI (−) DAD: 270, 310, 350, 520 nm; IT–MS: ESI (+) (−)

[15]

DAD: 200–450, 220, 280, 335 nm; IT–MS: APCI (+) DAD: 270 nm; ESI (+)

[81]

DAD: 210–400, 350 nm

[20]

DAD: 240,330, 360 nm; TOF–MS: ESI (–) DAD: 240, 330, 360 nm

[114]

DAD: 240, 360 nm; QTOF–MS: ESI (−)

[129]

DAD: 283 nm ELSD: 50 ◦ C

[30]

DAD: 215–420 nm; IT–TOF–MS: ESI (−)

[73]

DAD: 200–500, 254 nm; VIS: 517 nm; Q–MS: ESI (−)

[93]

TOF–MS: ESI (−)

[92]

UV: 270 nm

[57]

Q–MS and QTOF–MS: ESI (−)

[84]

DAD: 203, 355 nm; IT–MS: APCI (−)

[158]

Lycium barbarum

SE: ethanol, with 50% acetone and 75% ethanol, respectively UE: 70% ethanol, 30 min × 2 times

Synergi hydro-RP 80A, 250 mm × 2.0 mm, 4 ␮m Inertsil C18 , 250 mm × 4.6 mm, 5 ␮m

Scutellaria baicalensis

UE: 60% ethanol, 40 min

Adinandra nitida

Shaking extraction: methanol, 40 ◦ C, 16 h

Flavonoids, caffeic acid derivatives

Chrysanthemum morifolium

UE: methanol–water (60:40, v/v), 40 kHz, 100 W, 60 min

Ultimate XB C18 , 250 mm × 4.6 mm, 5 ␮m Hypersil C18 , 250 mm × 4.6 mm, 5 ␮m Symmetry C18 , 250 mm × 4.6 mm, 5 ␮m

Flavonoids, caffeoylquinic acids Flavonoids, catechins, chlorogenic acid, epicatechin Flavonoids, fingerprint

Three Compositae plants

Shaking extraction: methanol, 900 rpm, 28 ◦ C, 30 min PLE: 80% methanol, 120 ◦ C, 1500 psi, static extraction time of 15 min, 1 static circle

Zorbax SB C18 , 150 mm × 2.1 mm, 3.5 ␮m Zorbax SB C18 , 250 mm × 4.6 mm, 5 ␮m

UE: methanol, 30 ◦ C, 50 min × 3 times

Hypersil C18 , 200 mm × 4.6 mm, 5 ␮m Zorbax Extend C18 , 250 mm × 4.6 mm, 5 ␮m Shim-pack CLC–ODS, 150 mm × 6 mm, 5 ␮m Eclipse C18 , 250 mm × 4.6 mm, 5 ␮m

Litsea coreana. var. lanuginosa Litsea coreana var. lanuginosa Lonicera japonica

UE: 50% methanol, 45 min

Lonicera spp.

UE: 50% methanol, 40 min

Favonoids, iridoids, organic acids

Lonicera japonica

UE: 70% methanol, 40 min

Flavonoids, isochlorogenic acids and triterpenoids Flavonoids, phenolic compounds

Ilex hainanensis

UE: methanol, 30 min

ZorBax SB-C18 , 250 mm × 4.6 mm, 5 ␮m

Morus alba

Infusion: 95% ethanol, 48 h

Ascentis® Express C18 , 150 mm × 4.6 mm, 2.7 ␮m

Flavonoids, phenylpropanoids, benzoic acid derivatives Favonoids, organic acids, iridoid glycosides

Taraxacum mongolicum

RE: methanol, 1.5 h × 3 times

Symmetry C18 , 250 mm × 4.6 mm, 5 ␮m

Lonicera spp.

RE: methanol, 1.5 h

Zorbax Extend C18 , 150 mm × 4.6 mm, 5 ␮m

Flavonoids (rutin, quercetin)

Eucommia ulmoides

Decoction: distilled water, 60 ◦ C, 1 h × 2 times

Shim-pack VP-ODS, 150 mm × 4.6 mm, 5 ␮m

Flavonoids, saponins

Gynostemma pentaphyllum

Gemini C18 , 250 mm × 4.6 mm, 5 ␮m

Flavonoid, saponins, polyacetylenes

Leaf and root of Panax ginseng

Shaking extraction: methanol, 60 ◦ C, 3 h; SPE: Strata-E C18 cartridge, elution with 0.1% formic acid/methanol (1:1, v/v) for flavonoids, and methanol for saponins PLE: methanol, 150 ◦ C, 1500 psi, static extraction time of 15 min, 1 static circle

Flavonoids, iridoids, phenolic acids

Prevail C18 rocket column, 33 mm × 7 mm, 3 ␮m

Gradient elution with 2% glacial acetic acid and acetonitrile, 1 mL/min, 25 ◦ C Gradient elution with 0.4% acetic acid and acetonitrile, 1 mL/min, 30 ◦ C Gradient elution with 0.4% acetic acid and acetonitrile, 0.8 mL/min Gradient elution with 0.2% formic acid and acetonitrile–methanol (5:1, v/v), 0.8 mL/min, 20 ◦ C Gradient elution with 0.2% formic acid and acetonitrile, 1 mL/min, 30 ◦ C Gradient elution with water and acetonitrile (both containing formic acid, pH = 3), 1 mL/min, 25 ◦ C Gradient elution with 0.1% acetic acid and methanol, 0.9 mL/min, 20 ◦ C

Gradient elution with 0.1% formic acid and acetonitrile–methanol (5:1, v/v) containing 0.05% formic acid, 1 mL/min, 25 ◦ C Isocratic elution with methanol–water–phosphoric acid (50:49.5:0.5, v/v), 1 mL/min, 25 ◦ C Gradient elution with 0.1% formic acid and methanol for flavonoids, 0.1% formic acid and acetonitrile for saponins, 1 mL/min, 30 ◦ C Gradient elution with water and acetonitrile, 2.5 mL/min, 30 ◦ C

[32] [123]

[21]

[112]

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Gynostemma pentaphyllum Rhodiola crenulata

Flavonoids, triterpenoids

Glycyrrhiza uralensis, Glycyrrhiza glabra

UE: methanol–water (7:3, v/v), 15 min

Infusion: 80% methanol, 60 C, 6 h

Centella asiatica Citri reticulatae pericarpium

Infusion: 90% ethanol, 1 h, UE: 90% ethanol, 30 min Shaking extraction: 60% ethanol, 15 min, 250 rpm

Rubus suavissimus

RE: water, 2 h

Alltech Prevail C18 , 250 mm × 4.6 mm, 5 ␮m

Geniposide

Gardenia jasminoides

UE: 90% methanol, 15 min

Ginsenosides

Panax ginseng

MAE: 70% ethanol, 400 kPa, 10 min

Panax quinquefolius

SE: 70% ethanol; MAE: 70% ethanol, 500 kPa, 15 min RE: methanol–water (4:1, v/v), 70 ◦ C, 1 h

Symmetry C18 , 150 mm × 3.9 mm, 5 ␮m Zorbax Eclipse XDB C18 , 250 mm × 4.6 mm, 5 ␮m Pinnacle C18 , 250 mm × 4.6 mm, 5 ␮m ␮Bondapak® , 150 mm × 4.6 mm, 10 ␮m Prevail C18 , 250 mm × 4.6 mm, 5 ␮m ZorBax SB-C18 , 250 mm × 4.6 mm, 5 ␮m Atlantis C18 , 150 mm × 4.6 mm, 5 ␮m

Fingerprint

◦

SE: 70% ethanol, 80 ◦ C, 5 h; MAE: 70% ethanol, 450 kPa, 125 ◦ C, 10 min RE: ethanol, 90 ◦ C, 2 h × 2 times; SPE: Supelclean LC-18 cartridge, elution with 95% methanol Infusion: 95% ethanol, 5 d; purification: counter-current chromatography, n-heptane–ethyl acetate–methanol–0.1% formic acid (pH = 2) (2:3:2:3, v/v/v/v) RE: methanol, 3 h

Homoisoflavonoids

Ophiopogon japonicus

Hydroxyl phenanthrenes, bibenzyls

Dendrobium chrysototxum

Isoflavonoids, saponins

Astragalus spp.

Isoliquiritigenin, iquiritin, glycyrrhizic acid Jujuboside A, jujuboside B, betulinic acid Lignans

Licorice

UE: 0.5 M 1-butyl-3-methylimidazolium bromide solution, 200 W, 40 min

Ziziphus jujuba Mill. Var. spinosa Cannabis sativa

SE: 95% ethanol, 6 h ◦

◦

PLE: n-hexane (90 C), acetone (90 C), acetone–water (100 ◦ C, 70:30, v/v), 2059 psi, static extraction time of 5 min, 2 static circle UE: menthanol, 1 h

UV: 254 nm

[130]

IT–MS: ESI (−) UV: 254 nm

[72]

UV: 205 nm MS: ESI (−)

[148]

DAD: 254 nm

[86]

DAD: 200–400, 205, 254 nm

[12]

DAD: 210–400 nm; Q–MS: ESI (+) UV: 203 nm; QTrap–MS: ESI (+) UV: 203 nm

[115]

DAD: 203 nm

[90]

ELSD: 40 ◦ C

[104]

DAD: 190–400, 296 nm; IT–MS: ESI (–)

[170]

Isocratic elution with methanol–water (60:40, v/v), 1 mL/min,

DAD: 200–400, 280 nm

[79]

ZorBax Extend C18 , 250 mm × 4.6 mm, 5 ␮m Kromasil C18 , 250 mm × 4.6 mm, 5 ␮m

Gradient elution with 0.2% formic acid and acetonitrile, 0.8 mL/min, 35 ◦ C Isocratic elution with methanol–water–acetic acid (65:35:2, v/v/v), 1 mL/min, 25 ◦ C

TOF–MS: ESI (−)

[97]

UV: 254 nm

[209]

Hypersil C18 , 250 × 4.6 mm, 5 ␮m KinetexTM PFP 50 mm × 2.1 mm, 2.6 ␮m

Gradient elution with 0.1% acetic acid and acetonitrile, 1 mL/min Gradient elution with water and acetonitrile (both containing 0.1% acetic acid), 0.3 mL/min, 30 ◦ C

ELSD: 45 ◦ C

[102]

ESI (−)

[160]

ZorBax SB-C18 , 250 mm × 4.6 mm, 5 ␮m

Gradient elution with water (containing 0.1% acetic acid, v/v) and acetonitrile, 1 mL/min, 45 ◦ C Gradient elution with 0.1% trifluoroacetic acid and acetonitrile, 1 mL/min, 35 ◦ C Isocratic elution with 25% (v/v) acetonitrile, 0.2 mL/min, 30 ◦ C Gradient elution with 0.2% formic acid and acetonitrile/methanol (60:40, v/v), 0.8 mL/min Gradient elution with 0.045% KH2 PO4 –0.05% triethylamine buffer (pH = 7.0) and acetonitrile, 1 mL/min, 35 ◦ C Gradient elution with 0.1% formic acid and methanol, 0.2 mL/min

DAD: 190–400 nm IT-MS: ESI (+)

[139]

UV: 254 nm

[159]

UV: 203 nm PAD

[141]

UV: 280 nm QqQ-MS: ESI (−) UV: 250 nm

[140]

DAD: 190–600, 280 nm; IT–MS: ESI (−)

[28]

Mightysil RP-18GP, 250 mm × 4.6 mm, 5 ␮m Alltech C18 , 250 mm × 4.6 mm, 5 ␮m LicrospherTM 100 RP–18e, 125 mm × 4.6 mm, 5 ␮m

Lignans (isomeric dibenzocyclooctadiene)

Schisandra chinensis

Lignans

Schisandra chinensis

Madecassoside, asiaticoside Metabolic profile

Centella asiatica

PLE: methanol, 125 ◦ C, static extraction time of 5 min, 1 static circle UE: 50% ethanol

Arctium lappa

UE: 70% menthanol (v/v), 30 min × 2 times

Shiseido Capcell pak MG II C18 , 250 mm × 4.6 mm, 5 ␮m Kinetex C18 , 100 mm × 2.1 mm, 2.6 ␮m Prodigy ODS3 100 A˚

Monosaccharides

Gynostemma pentaphyllum

Infusion: distilled water (1:10, w/v), 80 ◦ C, 3h

250 mm × 4.6 mm, 5 ␮m Venusil RP-C18 , 250 mm × 4.6 mm, 5 ␮m

Monomeric and oligomeric flavan-3-ols

barley

Shaking extraction: acetone–water (70:30, v/v), 20 min × 2 times

LiChroCart RP-18 125 mm × 3.0 mm, 3 ␮m

[152] [101] J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Licorice

Gradient elution with 10 mM KH2 PO4 (pH = 4.6) and acetonitrile–water (4:1, v/v), 0.8 mL/min Gradient elution with 0.1% acetic acid and acetonitrile–water (4:1, v/v), 0.8 mL/min Gradient elution with 10 mM phosphate buffer (pH = 2.5) and acetonitrile, 1.2 mL/min, 40 ◦ C Gradient elution with water and acetonitrile, 1 mL/min, 30 ◦ C Gradient elution with water and methanol (both containing 0.1% acetic acid), 1 mL/min, 25 ◦ C Gradient elution with water and acetonitrile (both containing 0.17% phosphoric acid), 1 mL/min, 25 ◦ C Gradient elution with 0.1% formic acid and acetonitrile, 1 mL/min, 30 ◦ C Gradient elution with water and acetonitrile, 1 mL/min, 25 ◦ C Gradient elution with water and acetonitrile, 1.5 mL/min, 25 ◦ C Gradient elution with water and acetonitrile, 1.2 mL/min Gradient elution with water and acetonitrile, 1.5 mL/min Gradient elution with 0.1% formic acid and acetonitrile, 0.5 mL/min, 25 ◦ C

Cosmosil 5 C18 -AR II, 250 mm × 4.6 mm, 5 ␮m

[60]

13

14

Table 4 (Continued) Analytes

Herbal teas

Oleanolic acid, ursolic acid, oridonin

Rabdosia rubescens

Ophiopogonins, ophiopogonones Phenols

Ophiopogon japonicus

Phenolic compounds

Lethariella cladonioides

Sample preparation UE: 70% ethanol (oleanolic acid), 90% ethanol (ursolic acid), 80% ethanol (oridonin), 55 ◦ C, 40 min UE: 75% ethanol, 120 min × 2 times, SPE: elution with methanol RE: 80% ethanol, 80 ◦ C, 3 h

Crataegus pinnatifida var. major Crataegus spp.

UE: 80% ethanol, 15 min × 3 times

Ilex kudingcha

Infusion: water, 95 ◦ C

Lilium lancifolium, Lilium pumilum Stevia rebaudiana

UE: 1 M HCl in 80% methanol, 25 ◦ C, 1 h

UE: 80% ethanol, 30 min

Vortex: methanol–water (1:1, v/v), 30 min

Platycosides

Platycodon grandiflorum

Infusion: methanol, 25 ◦ C

Saponins

Lonicera spp.

UE: 50% methanol, 40 min

Panax notoginseng

PLE: methanol, 150 ◦ C, static extraction time of 15 min, 1000 psi, 1 static cycle MAE: methanol–water (1:1, v/v) acidified with HCl in 15 min

Phenolic acids, flavonoids

Lycium barbarum

Polyphenol compunds

Lophatherum gracile

Separation conditions

Detection

Ref.

LiChrospher C18 , 250 mm × 4 mm, 5 ␮m

Gradient elution with 0.1% phosphoric acid and acetonitrile, 1–1.5 mL/min, 40 ◦ C

UV: 210 nm, 240 nm

[9]

Luna C18 , 150 mm × 2.1 mm, 5 ␮m Amethyst C18 , 250 mm × 4.6 mm, 5 ␮m Prodigy RP-18 ODS (3), 250 mm × 4.6 mm, 5 ␮m Prodigy RP-18 ODS (3), 250 mm × 4.6 mm, 5 ␮m ODS–80TsQA 250 mm × 2.0 mm, 5 ␮m Hibar RT Lichrospher SB-C18 , 250 mm × 4.0 mm, 5 ␮m Alltech Intersil C18 , 150 mm × 4.6 mm, 5 ␮m

Gradient elution with water and acetonitrile (both containing 0.02% acetic acid), 0.2 mL/min Gradient elution with water and methanol, 1 mL/min, 25 ◦ C Gradient elution with 0.5% formic and acetonitrile–methanol (80:20, v/v), 1 mL/min Gradient elution with 0.5% formic and acetonitrile–methanol (80:20, v/v), 1 mL/min Gradient elution with 1% formic acid and methanol, 0.2 mL/min, 40 ◦ C Gradient elution with 1% acetic acid and acetonitrile, 0.5 mL/min, 40 ◦ C Gradient elution with NH4 H2 PO4 (pH = 2.5), acetonitrile–NH4 H2 PO4 (80:20, v/v), and phosphoric acid (pH = 1.5), 1 mL/min Gradient elution with 3% acetic acid and methanol, 0.8 mL/min, 30 ◦ C Gradient elution with 0.5% formic acid and acetonitrile–water (94:6, v/v), 1 mL/min, 30 ◦ C

QTOF–MS: ESI (−)

[169]

DAD: 262 nm; IT–MS: ESI (−) DAD: 280, 360, 520 nm; QqQ–MS: ESI (+) DAD: 280 nm; QqQ–MS: ESI (+) UV: 326 nm; Q–MS: ESI (−)

[44]

DAD: 200–400 nm

[210]

UV: 280, 320 nm

[37]

DAD: 278 nm

[74]

DAD: 280 nm; QqQ–MS: ESI (−)

[85]

UV 331 nm

[149]

QqQ–MS: ESI (−)

[211]

ELSD: 70 ◦ C

[75]

ELSD: 110 ◦ C

[112]

DAD: 203 nm; IT–MS: ESI (–) DAD: 220 nm; IT–MS: ESI (+)

[212]

UV: 206 nm

[108]

ELSD: 96 ◦ C IT–MS: ESI (−)

[29]

FLD: ex 290 nm, em 330 nm

[98]

QqQ-MS: ESI (+) (−)

[100]

®

Eclipse XDB-C18 , 250 mm × 4.60 mm, 5 mm Vydac 201TP54 C18 , 250 mm × 4.6 mm, 5 ␮m Elite SinoChrom BP C18 250 mm × 4.6 mm, 5 ␮m Eclipse Plus C18 , 100 mm × 4.6 mm, 3.5 ␮m Chemcobond 3.5-ODS-H, 150 mm × 4.6 mm, 3.5 ␮m

Shim-pack CLC–ODS, 150 mm × 6 mm, 5 ␮m Zorbax SB-C18 , 250 mm × 4.6 mm, 5 ␮m Xterra C18 , 150 mm × 3.9 mm, 5 ␮m

Senkirkine, senecionine

Tussilago farfara

Triterpenic glycosides

Centella asiatica

SE: methanol, 8 h

Triterpenoids

Ilex hainanensis

UE: methanol, 30 min

Vitamin E

Coix lacryma-jobi

Shaking extraction: 1% ascorbic acid in ethanol (w/v), 80 ◦ C, 10 min, then add 44% KOH for saponification, 80 ◦ C, 18 min, cool in ice bucket, add 50% n-hexane, centrifugation, collect n-hexane layer. Process 3 times. Wash n-hexane layer with water, passed through anhydrous Na2 SO4 , concentration and dissolve in isooctane.

Supelcosil LC-Si, 250 mm × 4.6 mm, 5 ␮m

Cassia obtusifolia

Infusion (70% ethanol, 30 min) followed by RE: 70% ethanol, 1.5 h ×2 times

Poroshell 120 EC-C18 , 100 mm × 2.1 mm, 2.7 ␮m

UHPLC, UHPLC–MS Anthraquinones, naphtha-␥-pyrone compounds

LiChroCART® RP18, 250 mm × 4 mm, 5 ␮m Shim-pack CLC-ODS, 150 mm × 6 mm, 5 ␮m

Gradient elution with 1.0% acetic acid and acetonitrile, 1.0 mL/min, 25 ◦ C Isocratic elution with 0.1% acetic acid–methanol (20:80, v/v), 0.3 mL/min, 25 ◦ C Gradient elution with 30 mM ammonium acetate buffer (pH = 4.81)–methanol–acetonitrile (75:5:20, v/v/v) and 69:5:26 (v/v/v), 0.7 mL/min, 40 ◦ C Gradient elution with 0.4% acetic acid and acetonitrile, 0.8 mL/min Gradient elution with water and acetonitrile, 1 mL/min, 25 ◦ C Gradient elution with 20 mM ammonium acetate and acetonitrile (both containing 0.1% formic acid), 0.7 mL/min, 40 ◦ C Gradient elution with water and acetonitrile, 1 mL/min Gradient elution with water and methanol–acetonitrile (5:1, v/v), 1 mL/min, 25 ◦ C Isocratic elution with isooctane:ethyl acetate:acetic acid:2,2-dimethoxy propane = 98.5:0.7:0.7:0.1, 1.5 mL/min

Gradient elution with 30 mM ammonium acetate–water and acetonitrile, 0.4 mL/min, 30 ◦ C

[124] [127] [59]

[18]

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Lycopus lucidus

Infusion: acetone–water (8:2, v/v), 50 ◦ C, 30 min × 2 times Shaking extraction: 50% ethanol, 90 ◦ C, 2 h; SPE: Strata-X polymer cartridge, elution with methanol Infusion: 70% menthanol 1 h, UE: 70% menthanol, 30 min ×2 times UE: methanol, 40 min × 3 times

Ziziphus jujuba

Column

Arctium lappa

UE: 70% methanol, 30 ◦ C, 60 min

Chemical profile

Sarcandra glabra

Flavonoids

Gynostemma pentaphyllum

UE: 70% acetonitrile containing 0.5% formic acid, 30 min UE: methanol, 30 min

Flavonoids, organic acids, synephrine, ␤-sitosterol, cyclic peptides Flavonol, triterpene glycosides Flavonols

Citrus reticulata or its cultivars

UE: methanol, 30 min

Zorbax SB C18 , 50 mm × 4.6 mm, 1.8 ␮m

Siraitia grosvenorii

UE: methanol, 1 h

Ginkgo biloba

UE: methanol–water (60:40, v/v), 1 h

ACQUITY HSS C18 , 100 mm × 2.1 mm, 1.7 ␮m Shim-pack XR-ODSII, 150 mm × 2 mm, 2.2 ␮m

Fingerprint (flavonoids)

Gynostemma pentaphyllum

SE: methanol, 6 h

Eclipse Plus C18 , 150 mm × 2.1 mm, 1.8 ␮m

Fingerprint, scoparone, alkaloids and bibenzyls Ginsenosides

Dendrobium spp.

PLE: 80% methanol, 140 ◦ C, static extraction time of 15 min, 1500 psi, 1 static cycle UE: 70% methanol, 1 h

ACQUITY UPLC BEH C18 , 50 mm × 2.1 mm, 1.7 ␮m HSS T3 , 100 mm × 2.1 mm, 1.8 ␮m

Panax ginseng

BlueOrchid C18 , 100 mm × 2.0 mm, 1.8 ␮m Hypersil GOLD, 100 mm × 2.1 mm, 1.9 ␮m Eclipse Plus C18 , 150 mm × 2.1 mm, 1.8 ␮m

Iridoid glycosides, saponins, flavonoids, phenolic acids, Metabolic fingerprint

Lonicera japonica Lonicera spp.

UE: methanol, 40 min

Zorbax SB C18 , 50 mm × 4.6 mm, 1.8 ␮m

Angelica sinensis

Metabolic profile

Aloe barbadensis

Infusion followed by UE: 70% methanol, infusion, 1 h UE, 40 min Shaking extraction: methanol, 12 h

ACQUITY UPLCTM BEH C18 100 mm × 2.1 mm, 1.7 ␮m BEH C18 , 100 mm × 2.1 mm, 1.7 ␮m BEH C18 , 50 mm × 2.1 mm, 1.7 ␮m HSS T3 , 100 mm × 2.1 mm, 1.8 ␮m

Schisandra chinensis Nucleosides, nucleobases

Ziziphus jujuba

Phenylethanoid glycosides Saponins

Ligustrum genus Panax notoginseng

UE: water, 75 ◦ C, 2 h, then UE the residue: methanol, 60 ◦ C, 3 h UE: water, 40 kHz, 30 min

Infusion followed by UE: water, 25 ◦ C, infusion, 10 h, UE, 25 min PLE: methanol, 150 ◦ C, static extraction time of 15 min, 1000 psi, 1 static cycle UE: methanol, 10 min; SPE, Oasys HLB polymer cartridge, elution with 70% methanol

BEH C18 , 100 mm × 2.1 mm, 1.7 ␮m ACQUITY UPLC BEH C18 , 50 mm × 2.1 mm, 1.7 ␮m HSS C18 100 mm × 2.1 mm, 1.8 ␮m for steviol; HSS C18 150 mm × 2.1 mm, 1.8 ␮m for steviol-glycosides;

Steviol, steviol-glycosides

Stevia rebaudiana

Triterpene saponins

Glycyrrhiza uralensis Fischer

UE: 60% ethanol, 30 min

Zorbax SB C18 , 50 mm × 4.6 mm, 1.8 ␮m

Schisandra chinensis

UE: n-hexane, 40 min × 2 times

D1: immobilized liposome chromatography column 5 mm × 4.6 mm; D2: Chromolith® Performance RP-18e, 100 mm × 4.6 mm,

LC × LC, LC × LC–MS Lignans

Gradient elution with 5% acetic acid and acetonitrile, 0.5 mL/min, 30 ◦ C Gradient elution with 0.1% formic acid and acetonitrile, 0.6 mL/min, 30 ◦ C Gradient elution with water and acetonitrile (both containing 0.1% formic acid), 0.25 mL/min, 45 ◦ C Gradient elution with 0.1% formic acid and acetonitrile, 0.5 mL/min, 25 ◦ C

DAD: 210–380 nm, UV: 330 nm DAD: 200–400 nm; LTQ–Orbitrap–MS: ESI (−) DAD: 190–400, 256 nm IT–MS: ESI (+) (−)

[143]

QqQ–MS: ESI (+)

[134]

Gradient elution with 0.1% formic acid and acetonitrile, 0.35 mL/min, 50 ◦ C Gradient elution with water and acetonitrile (both containing 0.1% formic acid), 0.5 mL/min, 40 ◦ C Gradient elution with water and acetonitrile (both containing 0.1% formic acid), 0.25 mL/min, 45 ◦ C Gradient elution with 20 mM phosphate buffer (pH = 7.1) and acetonitrile, 0.4 mL/min, 4 ◦ C Gradient elution with water and acetonitrile (both containing 0.1% formic acid), 0.5 mL/min, 40 ◦ C Gradient elution with 0.1% formic acid and acetonitrile, 0.6–0.8 mL/min, 22 ◦ C

QTOF–MS: ESI (−)

[131]

TOF–MS: ESI (+) (−)

[213]

DAD: 190–400, 256 nm; IT–MS: ESI (+) (−)

[106]

DAD: 210 nm

[214]

QTOF–MS: ESI (−)

[132]

DAD TOF–MS: ESI (+) (−)

[118]

TOF–MS: ESI (+)

[147]

QTOF–MS: ESI (–)

[88]

Q-MS: ESI (+)

[69]

DAD 254, 269, 273 nm; QTOF–MS: ESI (+)

[121]

DAD: 190–400, 310 nm

[43]

UV: 203 nm

[215]

QqQ–MS: ESI (−)

[35]

TOF–MS: ESI (+)

[126]

UV: 254 nm QqQ–MS: ESI (+)

[142]

Gradient elution with 0.1% formic acid and acetonitrile, 0.4 mL/min, 30 ◦ C Gradient elution with water and acetonitrile (both containing 0.1% formic acid), 0.3 mL/min Gradient elution with 0.1% formic acid and acetonitrile, 0.25 mL/min, 40 ◦ C Gradient elution with 5 mM ammonium acetate solution (pH = 8.0) and methanol, 0.3 mL/min, 30 ◦ C Gradient elution with 0.1% phosphoric acid and acetonitrile, 0.4 mL/min, 35 ◦ C Gradient elution with water and acetonitrile, 0.35 mL/min, 45 ◦ C Isocratic elution with 5 mM ammonium acetate (pH = 6)–acetonitrile (45:55, v/v) for steviol, 0.6 mL/min, 60 ◦ C; gradient elution with 2 mM ammonium acetate (pH = 6.5)/0.1% CH2 Cl2 in acetonitrile for steviol-glycosides, 0.5 mL/min, 80 ◦ C Gradient elution with 0.2% formic acid and acetonitrile–methanol (2:1, v/v), 0.7 mL/min, 25 ◦ C D1: isocratic elution with 10 mM ammonium acetate solution (pH 6.8), 1 mL/min; D2: gradient elution with water and acetonitrile, 3 mL/min

[16] [133]

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Caffeoyl esters

15

[122]

[56]

[39]

IT–MS: ESI (−)

UV: 203 nm QqQ–MS: ESI (+) (−)

DAD: 220 nm

D1: gradient elution with 5% acetonitrile and 95% acetonitrile in 0.1% formic acid, 50 ␮L/min; D2: isocratic elution with 20% and 70% acetonitrile in 0.1% formic acid, 1 mL/min D1: gradient elution with water and acetonitrile, 1 mL/min, 30 ◦ C; D2: gradient elution with water and acetonitrile in 0.1% formic acid, 0.2 mL/min, 30 ◦ C Gradient elution with water and acetonitrile, 30 ◦ C, D1: 20 mL/min, D2: 1 mL/min D1: XCharge C18 , 150 mm × 4.6 mm, 10 ␮m; D2: XAmide (HILLIC), 150 mm × 4.6 mm, 5 ␮m Stevia rebaudiana Steviol glycosides

Saponins

Panax notoginseng

UE: water, 30% methanol, 50 methanol, 70% methanol, methanol, 10 min × 3 times SPE: Sep-Pak C18 cartridge, elution with 70% methanol Decoction: water × 2 times (120 min, 90 min), SPE: Al2 O3 cartridge, elution with methanol, C18 cartridge, elution with methanol RE: water, 4 h Platycodon grandiflorum Platycosides

D1: YMC-Pack PA-G, 250 mm × 1 mm, 5 ␮m; D2: Zorbax SB-C18 , 30 mm × 2.1 mm, 1.8 ␮m D1: Luna C18 , 150 mm × 1 mm, 5 ␮m; D2: Luna NH2 , 50 mm × 3 mm, 3 ␮m Vortex: acetonitrile–water (80:20, v/v)

APCI, atmospheric pressure chemical ionization; DAD, diode array detection; ELSD, evaporative light-scattering detection; ESI, electrospray ionization; FLD, fluorescence detection; HPLC, high performance liquid chromatography; LC × LC, comprehensive two-dimensional liquid chromatography; MS, mass spectrometry; PAD, pulsed amperometric detection; QqQ, triple quadrupole; TOF, time-of-flight; UV, ultraviolet detection.

[36] DAD: 200–400, 210, 280 nm Gradient elution with water and acetonitrile (pH = 3, adjusted by H3 PO4 ), D1: 20 ␮L/min; D2: 3.4 mL/min, 70 ◦ C

Column Sample preparation

Stevia rebaudiana Glycosides

Analytes

Herbal teas

D1: XAmide 150 mm × 4.6 mm, 5 ␮m; D2: ACQUITY UPLC BEH C18 , 100 mm × 2.1 mm, 1.7 ␮m

Ref. Detection Separation conditions

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Table 4 (Continued)

16

Herbal tea usually contains bioactive substances with acidic or basic group(s), therefore, a certain pH value of the mobile phases is required during the HPLC separation. Optimized mobile phase pH can increase the retention of the acidic or basic compounds, which results in the improvement of peak shape and detection sensitivity. Acidic pH modifiers can be formic acid [69,105,140], acetic acid [20,57,86,91,102,112,138,139,143,149,160,209] or their ammonium salt [58,75,100,142], as well as phosphoric acid [9,26,57,76,99,109] and phosphate buffer [37,60,72,130] solutions, while basic modifier is mainly used triethylamine [125,151]. The applications of HPLC in herbal tea analysis were summarized in Table 4. 4.2.1.2. Ultra high performance liquid chromatography. Currently, popularity in the application of ultra-high performance liquid chromatography (UHPLC) with sub-2 ␮m particle size has increased. The commercial sub-2 ␮m particle size columns, such as ultraperformance LC (UPLC, Waters Corporation, 1.7-␮m or 1.8-␮m porous particles) [35,43,88,96,121,131,132,147,215] and rapid resolution LC (RRLC, Agilent Technologies, 1.8-␮m porous particles or 2.7-␮m porous shell particles) [100,106,118,126,133,134] have been used in the phytochemical analysis of herbal tea. UHPLC could provide up to 4 times faster analysis than HPLC on conventional column without sacrificing resolution [216]. 4.2.1.3. Comprehensive two-dimensional liquid chromatography. Being an alternative way of maximizing chromatographic separation like GC × GC, comprehensive two-dimensional liquid chromatography (LC × LC) systems can lead to substantially improved analytical performances over the single-column approaches to meet the analysis demands of extremely complex components. The combination of two different separation systems draws on all of the available resolving power from each of the dimensions to separate the components in the sample of great complexity. Regarding phytochemical analysis of herbal tea, LC × LC analysis in Platycodon grandiflorum [122], P. notoginseng [56,217], S. chinensis [142] and S. rebaudiana [36,39] have been reported. Fu et al. [39] developed a two-dimensional RPLC/hydrophilic interaction liquid chromatography (HILIC) method for the characterization of steviol glycosides in S. rebaudiana in offline mode. The system exhibited excellent separation ability for the analysis of complex Stevia sample and represented an efficient tool for detection of low-abundance glycosides. 4.2.2. Detection 4.2.2.1. Ultraviolet detection and diode array detection. Ultraviolet detection (UV) [9,26,37,57,60,62,64,72,91,99,101,108,109,125, 130,138,140,141,143,148,149,151,159,209,215] and diode array detection (DAD) [20,36,39,43,55,58,74,76,86,90,105,139,143,210] in combination with different LC systems have been widely used in phytochemical analysis of herbal tea due to their advantages of desirable sensitivity and excellent reproducibility. UV is generally carried out at a/several specific wavelength(s), while DAD enables the acquirement of a wavelength range of at least 200–400 nm, providing UV spectral information for qualitative analysis of each peak in a chromatogram (Table 4). However, they are not suitable for detection of non-chromophoric compounds with little or no UV absorption. 4.2.2.2. Evaporative light-scattering detection. Evaporative lightscattering detection (ELSD) is considered to be an alternative choice for the detection of many non-UV-absorbing substances including carbohydrates, triterpenoids, lipids, amino acids, as well as fatty acids. ELSD is a quasi-universal and mass-dependent detector, and it can produce more uniform detection sensitivity for most analytes, regardless of their physical and chemical properties. For analysis

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

mAU

UV

4

30 25 20 15 10 5 0

3

2 1 0

mV

10

20

30

40

50

60

min

ELSD

1000

6

800 600 400 200 0

7

5

8 0

10

20

30

40

50

60

min

Fig. 2. HPLC–DAD–ELSD chromatograms of 8 bioactive compounds in Ilex hainanensis. 1, rutin; 2, eriodictyol-7-O-␤-d-glucopyranoside; 3, isochlorogenic acid A; 4, isochlorogenic acid C; 5, ilexhainanoside D; 6, ilexsaponin A1; 7, ilexgenin A; 8, ursolic acid. Reprinted from Ref. [30] with permission of MDPI.

of herbal tea, different phytochemicals, such as platycosides in P. grandiflorum [75], triterpenoids in Ziziphus species [102,120], ginsenosides in P. ginseng [218], P. notoginseng [219,220] and Panax quinquefolius [104], and triterpenoids in Ilex hainanensis [29,30], have been successfully detected by using HPLC–ELSD. In addition, ELSD can be hyphenated after DAD and forms an on-line coupled HPLC–DAD–ELSD system, affording as many comprehensive information as possible for a phytochemical analysis (Fig. 2) [30]. The deficiencies of ELSD are the relatively low sensitivity and lack of structural information. Moreover, ELSD is preferably used when the analytes are less volatile than the mobile phases (Table 4). 4.2.2.3. Mass spectrometry (MS). MS, especially high-resolution MS and tandem MS, serves not only as a detector with high sensitivity and excellent selectivity but also as a powerful approach for identification of the bioactive components according to the molecular weight and fragmentation measurements. LC–MS, in particular UHPLC–MS and LC × LC–MS, has greatly facilitated the efficient separation, high sensitivity, and excellent specificity for the qualitative and quantitative analysis of phytochemicals. In addition, MS can readily follow LC–DAD and form a LC–DAD–MS system, providing both on-line UV and MS information for each individual peak in a chromatogram. As a result, the identification and quantification of the phytochemicals become more accurate. Different types of mass analyzer including quadruple (Q) [59,62,69,82–84,93,115], ion trap (IT) [8,15,18,29,44, 81,94,96,106,122,123,130,133,139,158,170,212,218], and timeof-flight (TOF) [54,92,97,114,118,126,146,147,213,221] have been employed for the phytochemical analysis of herbal tea. In addition, tandem MS in the combination of same or different mass analyzers including triple quadrupole (QqQ) Q–Trap [35,56,58,61,78,85,100,113,124,127,134,140,142,211], [32,40,152], Q–TOF [88,91,95,120,121,129,131,132,169], IT–TOF [73] and LTQ–Orbitrap [16] have also been applied in herbal tea analysis. The aim of tandem MS is to get a higher level of mass structural information than those obtained by a single mass analyzer and/or to achieve better selectivity and sensitivity for quantitative analysis. Among these tandem MS techniques, Q–TOF, IT–TOF and LTQ–Orbitrap are preferable to perform structure elucidation or confirmation with high sensitivity, high mass resolution and high accuracy, especially for non-targeted phytochemicals.

17

High-resolution tandem mass spectrometer offers MS/MS or MSn experiments for accurate mass measurements, which provides not only multi-stage fragmentation information but also elemental composition of parent and fragment ions. This is greatly beneficial to identify unknown compounds and isobaric compounds [73,91,129,131,132]. Dugo et al. [73] utilized hybrid IT–TOF-MS to characterize 22 phenolic compounds present in Morus alba leaves. The employment of the hybrid mass spectrometer allows the structural assignments of a series of structural isomers, and 11 of the 22 compounds were reported in M. alba leaves for the first time. Zhang et al. [132] employed an UPLC–QTOF-MS/MS-based metabolomics approach for rapidly evaluation of the holistic qualities and exploration of the characteristic chemical components of commercial white and red ginseng. With this approach, 51 major peaks were separated and 43 compounds including 3 sulfurcontaining compounds were identified, and certain quality issues referring to processing procedures of the products were revealed. Together with ginsenoside Rg3 , a new nitrogen-containing component and ginsenoside 20(R)-Rh1 were found to be characteristic components of red ginseng, while malonyl ginsenoside Rb1 /isomer and malonyl ginsenoside Rg1 /isomer were determined to be characteristic components of white ginseng. QqQ and Q–Trap mass spectrometers working in MRM present excellent sensitivity and selectivity in monitoring the targeted compounds, which have been frequently used for quantitative analysis of phytochemicals in herbal tea [58,61,113,216]. To quantitatively analyze the antioxidant compounds in Houttuynia cordata, Nuengchamnongn et al. [61] developed a LC–MS/MS method via MRM with optimized mass transition ion pairs, and the validated results showed desirable linearity, precision and accuracy. Liu et al. [40] demonstrated an HPLC–Q–Trap–MS method using MRM mode with switching of ESI source polarity between positive and negative modes for simultaneous determination of 27 components in Isodon serra. To maximize the structural information obtained in a single LC–MS/MS analysis, an information-dependent acquisition (IDA) method, which combines two or more different scanning modes in a sequential fashion, was used to trigger product-ion scans above the MRM signal threshold. LC × LC–MS, as a very powerful hyphenated technique for the identification and determination of phytochemicals, has also been introduced into herbal tea analysis. Jeong et al. [122] developed HPLC × HPLC–MS methods to analyze the platycosides present in P. grandiflorum. The high orthogonality of C18 × NH2 columns combination provided a powerful separation for analyzing platycosides in P. grandiflorum. With this increased peak capacity, three minor peaks and five isomers, which were not identified by a single C18 column, were chromatographically separated (Fig. 3). Table 4 summarized the applications of LC–MS in phytochemical analysis of herbal tea.

4.3. Electromigration techniques Capillary electrophoresis (CE) is a powerful separation tool which has been developed rapidly and matured since its invention, and it has become a hot study area in phytochemical analysis of natural plants in recent years [222,223]. Compared with the conventional chromatographic methods, CE has many advantages such as excellent separation efficiency, high resolution, short analysis time, being easy to automate, and low solvent and sample consumption. Although CE has many modes, CZE is much more widely used in herbal tea analysis. Another electromigration technique which has been introduced to the field of herbal tea analysis in recent years is capillary electrochromatography (CEC) [33,157,222–224]. Actually, CEC is a hybrid technique of LC and CE which uses an electric field to drive liquid through a packed

18

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Fig. 3. Schematic diagram of LC × LC system (a), GC × GC–TOF-MS chromatograms of two dimensional plots of platycoside extract on C18 × NH2 on the basis of the TIC (b), and extended 2D plots of three different time windows in first dimension (C18 ) from 65 to 90 min (c), 130 to 163 min (d), and 175 to 195 min (e) Reprinted with modification from Ref. [122] with permission of Elsevier.

capillary column, and the best properties of HPLC and CE operate in synergy in this technique [157]. It should be noted that electrolyte system (buffer) is necessary during the process of electromigration analysis, and the optimization of the corresponding parameters includes buffer pH, buffer type and concentration, additives, voltage, temperature, injection mode, capillary length and inside diameter of the column [223–225]. Many strategies involving univariate design, orthogonal design, uniform design, central composite design, and genetic algorithm are used to optimize the parameters for achieving the best resolution and analysis time [223–225], and univariate design is common used in herbal tea analysis [89,111,116,119,157,226]. As for the detection, the majority of commercially available CE instruments employ UV or DAD as detection because of their advantages of simplicity, convenience and availability, and UV or DAD are widely used for the detection of bioactive components with UV absorption in herbal tea [89,136,137,157,227,228]. Electrochemical detection (ECD) is also widely employed in CE analysis of herbal tea because it provides high sensitivity and good selectivity for electroactive substances [110,119]. In addition, ECD can be easily miniaturized with little or no loss in sensitivity. Amperometric detection (AD) was also coupled with CE to provide high sensitivity and good selectivity for the determination of electroactive constituents in herbal tea [111,116,226,229]. CE and CEC applications in herbal tea analysis were summarized in Table 5. 4.4. Ambient mass spectrometry Ambient mass spectrometry (AMS) [230] is a novel developed technique allowing the analysis of samples under ordinary ambient

conditions with minimal or no sample pretreatment and without chromatographic separation. AMS has developed rapidly since the introduction of desorption electrospray ionization (DESI) [231] by Cooks et al. of Purdue University in 2004. Besides DESI, a series of AMS techniques such as direct analysis in real time (DART) [232], extractive electrospray ionization (EESI) [233,234], desorption atmospheric pressure chemical ionization (DAPCI) [235,236], low-temperature plasma (LTP) [237], paper spray (PS) [238,239], leaf spray [240,241], and tissue spray [242] have also been developed in the past few years. As mentioned above, herbal tea usually contains a wide range of constituents with diverse chemical properties. Characterization of these phytochemicals has been dominated by conventional chromatography-based or MS-based methods owing to their excellent analytical performances such as high sensitivity, good specificity, high accuracy, wide applicability, and both qualitative and quantitative capability with reasonable precision. However, multi-step sample pretreatment must be performed prior to instrumental analysis. Additionally, a long chromatographic run time is necessary to separate a wide variety of constituents. These conventional techniques are therefore time consuming and cannot meet the requirements of rapid and high-throughput analysis. With the rapidly increasing consumption of herbal tea, there is an urgent need to develop rapid yet reliable analytical techniques for their quality assessment and control. The perfect high-throughput phytochemical analysis technique for quality assessment and control of herbal tea should possess the following merits: (1) capability to provide as much information as possible at the molecular level; (2) possessing the ability of rapid and high-throughput monitoring without cross-contamination and memory effects; (3) excellent

Table 5 Applications of electromigration techniques in the phytochemical analysis of herbal tea. Herbal teas

Sample preparation

Column

Separation conditions

Detection

Ref.

CE Flavonoids

Centella asiatica

UE: methanol, 60 ◦ C, 30 min

Fused silica capillary, 58.5 cm × 75 ␮m, 8.5 cm to deterctor

UV: 220 nm

[137]

Chrysanthemum indicum

UE: methanol, 60 min × 3 times

Fused silica capillary, 70 cm × 25 ␮m

AD: +0.9 V (vs. SCE)

[116]

Leonurus heterophyllus

UE: ethanol, 30 min × 2 times

Fused silica capillary, 60 cm × 25 ␮m,

AD: +0.95 V (vs. Ag/AgCl)

[229]

Morus alba

UE: ethanol–water (4:1, v/v), 30 min

Fused silica capillary, 75 cm × 25 ␮m

20 mM NaH2 PO4 –Na2 HPO4 (pH = 8.0) containing 10% (v/v) ACN and 6% (v/v) MeOH, +25 kV, 30 ◦ C 36 mM borate–phosphate buffer (pH = 8.8) with 3.0 mM ␤-CD, +18 kV 50 mM Na2 B4 O7 –100 mmoL/L NaH2 PO4 buffer (pH = 7.50), +15 kV 50 mM H3 BO3 –Na2 B4 O7 (pH = 9.2), +16 kV

AD: +0.95 V (vs. SCE)

[111]

Panax ginseng

SE followed by UE: SE, chloroform, 3 h, UE:, water-saturated n-butanol, 30 min RE: methanol–water (1:1, v/v), 60 ◦ C, 25 min

Fused silica capillary, 50 cm × 55 ␮m

20 mM borate in 30% methanol (pH = 9.67), +18 kV

UV: 203 nm

[227]

Fused silica capillary, 8.5 cm × 50 ␮m

Carbonate buffer (25 mM, pH = 10)–methanol–ethylene glycol (80:10:10, v/v/v) containing 0.4% ␤-CD, −25 kV, 25 ◦ C 140 mM sodium cholate in methanol buffer, 25 ◦ C, 25 kV

UV: 254 nm

[89]

UV: 227 nm

[136]

180 mM borate buffer (pH 10.3), +15 kV

UV: 245 nm

[228]

50 mM borax buffer (pH 8.7), +16 kV 80 mM H3 BO3 –Na2 B4 O7 (pH 9.0), +16 kV

ED: +0.9 V (vs. SCE)

[110]

ED: +0.95 V (vs. SCE)

[119]

Flavonoids, cumarins, organic acids Ginsenosides

Glycyrrhizin, 18␣-glycyrrhetic acid, 18␤-glycyrrhetic acid Lignans

Monosaccharides (hydrolysates of polysaccharides) Phenolic acids, flavones Phenols

Rutin, quercetin, esculin, esculetin CEC Flavonoids

Licorice

Schisandra chinensis

UE: methanol, 1 h

Polygonatum odoratum

RE: 80% ethanol, 1 h, RE the residue, water, 1 h, then degradate with 95% H2 SO4 , 1 h UE: 80% methanol, 2 h

Lonicera japonica Lycium barbarum

Sophora japonica

Adinandra nitida Licorice

UE: doubly distilled water, 50% ethanol, 80% ethanol, 95% ethanol, 60 min Far infrared-assisted extraction: methanol, 6 min, 150 V Shaking extraction: methanol, 40 ◦ C, 16 h PLE: 70% ethanol, 100 ◦ C, static extraction time of 5 min, 1 cycle

Fused silica capillary, 47 cm × 50 ␮m, 40 cm to detector Fused silica capillary, 50 cm × 50 ␮m, 40 cm to detector Fused silica capillary, 75 cm × 25 ␮m Fused silica capillary, 75 cm × 25 ␮m Fused silica capillary, 40 cm × 25 ␮m

50 mM borate buffer (pH = 9.2), 15 kV

AD: +0.9 V (vs. SCE)

[226]

Monolithic column

10 mM ammonium formate buffer (pH = 3.0), +10 kV 10 mM phosphate buffer (pH = 3.0)/ACN (65:35), +25 kV, 30 ◦ C

UV: 260 nm

[33]

DAD: 254, 275, 360, 405 nm

[157]

Hypersil C18 capillary 25 cm × 3 ␮m

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Analytes

AD, amperometric detection; CE, capillary electrophoresis; CEC, capillary electrochromatography; DAD, diode array detection; ECD, electrochemical detection; UV, Ultraviolet detection.

19

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J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

Fig. 4. Tissue spray–MS for in situ chemical analysis of American ginseng. Pro, proline; Val, valine; Ile, isoleucine; Leu, leucine; Gln, glutamine; Lys, lysine; His, histidine; Arg, arginine; GABA, gamma-aminobutyric acid; Di, disaccharide; Tri, trisaccharide. Reprinted with modification from Ref. [242] with permission of Wiley-VCH.

specificity for the detection of analytes in complex matrices. AMS is an alternative choice that possesses the above-mentioned merits. Recently, direct analysis of phytochemicals from herbal tea raw plants has been demonstrated by using different AMS methods such as leaf spray [240,241], tissue spray [242], and DESI [243]. These techniques gave the merits of high sensitivity and excellent specificity, easy to implement with no need for sample preparation and chromatographic separation. A wide range of phytochemicals have been rapidly detected by using these techniques. In the case of Stevia glycosides, leaf spray–MS has been performed directly on fresh Stevia leaves for rapid identification and characterization of the diterpene glycosides by Zhang et al. [241], and the characteristic constituents of the Stevia plant were observed in both positive- and negative-ion detection mode. The presence of

glycosides was confirmed via tandem mass spectrometry analysis using collision-induced dissociation (CID) and further supported by exact mass measurements using an LTQ–Orbitrap–MS. Besides, semi-quantitative analysis of glycosides was also performed. Tissue spray–MS was performed to analyze phytochemicals of Panax quinquefolium (American ginseng) by Chan et al. [242]. Using the optimized conditions, abundant phytochemicals including ginsenosides, amino acids and oligosaccharides could be directly detected from the tissues of American ginseng (Fig. 4). It should be noted that AMS is extremely suitable for the analysis of highly polar saccharides, of which are difficult to analyze by RP-HPLC because of their extremely weak retention. As a novel developed technique, the applications of AMS in the analysis of herbal tea and other natural products are still very

J. Zhao et al. / J. Chromatogr. A 1313 (2013) 2–23

limited. In spite of that, AMS gives a vital extension to the conventionl scope of mass spectrometry, with promising prospects in rapid screening and characterization of herbal tea raw materials. 5. Future outlooks and conclusions The safety, efficacy and quality of herbal tea are the main concerns and mostly dependent on phytochemical analysis, which requires suitable sample pretreatment and instrumental analysis. As state above, several classical and advanced sample pretreatment techniques as well as conventional and novel developed analytical methods have been used for phytochemical analysis of herbal tea, which provide valuable chemical information for their quality, safety and efficacy assessments. Among these methods, classical and conventional techniques are still widely used, while novel methods, such as comprehensive multi-dimensional chromatography and ambient mass spectrometry, are limited. Especially, most sample preparation for phytochemical analysis of herbal tea used organic solvents, which was not in accordance with traditional administration form. Therefore, carefully investigation of watersoluble components of herbal tea is necessary. In addition, the huge analytical potential of foodomics, a discipline that studies the food and nutrition domains through the application of advanced omics technologies, can allow solving questions related to food safety, traceability, quality [244]. Foodomics also can be an adequate strategy to investigate the complex issues, such as herbal tea. These studies should be improved in future. Acknowledgements This research was supported by grants from the Science and Technology Development Fund of Macao (028/2007/A2 and 059/2011/A3), and the University of Macau (MYRG140 and MYRG085). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]

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