Recent developments in sample preparation techniques for chromatography analysis of traditional Chinese medicines

Journal of Chromatography A, 1153 (2007) 90–96

Review

Recent developments in sample preparation techniques for chromatography analysis of traditional Chinese medicines Chunhui Deng a , Ning Liu b , Mingxia Gao a , Xiangmin Zhang a,∗ a

b

Department of Chemistry, Fudan University, Shanghai 2004433, China Center for Analysis & Measurement, Fudan University, Shanghai 2004433, China Available online 27 January 2007

Abstract Traditional Chinese medicines (TCMs) have a long history dating back thousands of years. Recently, there has been increasing interest worldwide in the use of TCMs for the prevention and treatment of various illnesses. In China, a large number of analytical tools, especially chromatographic techniques have been used to analyze the constituents of TCMs in order to control their quality and discover new bioactive compounds. In this paper, recent developments in sample preparation techniques for the extraction, clean-up, and concentration of analytes from TCMs are compared. These techniques include headspace solid-phase microextraction (HS-SPME), headspace liquid-phase microextraction (HS-LPME), microwave-assisted extraction (MAE), supercritical-fluid extraction (SFE), pressurized-liquid extraction (PLE), and microwave distillation (MD). © 2007 Elsevier B.V. All rights reserved. Keywords: Sample preparation; Traditional Chinese medicines; Extraction; Chromatographic analysis

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample preparation techniques for TCMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Headspace extraction techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1. HS-SPME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2. HS-LPME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Microwave-assisted extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Pressurized-liquid extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Supercritical-fluid extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5. Microwave distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Traditional Chinese medicines (TCMs) have the long history over thousands of years. The origin of TCMs was associated with the legendary testing of many herbs for their medicinal properties by the folk hero, Shen Nong [1]. His experience and work was recorded in Shen Nong Ben Cao Jing (The Herbal

∗

Corresponding author. Tel.: +86 21 65643983; fax: +86 21 65641740. E-mail address: [email protected] (X. Zhang).

0021-9673/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2007.01.081

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Classic of the Divine Plowman) in about 2700 B.C. In the Ming Dynasty (1368–1644), a major medical work Ben Cao Gang Mu (The Comprehensive Herbal Foundation) written by Li Shi-Zhen in 1590 discussed 1892 medicinal substances and contained over 1000 illustrations with over 10,000 medicinal formulations, which indicated a comprehensive pharmaceutical knowledge and clinical experience. So far, 12,806 medical resources have been found in China, including 11,145 medicinal plants, 1581 medicinal animals, and 80 medicinal minerals [2]. Furthermore, a total of 2375 products have been compiled in the Pharmacopoeia of People’s Republic of China (2000

C. Deng et al. / J. Chromatogr. A 1153 (2007) 90–96

edition) [3]. Such natural medicinal resources provide valuable material for the discovery and development of new drugs of natural origin. Some active components have been discovered from these Chinese medical products with anti-cancer, anti-bacterial, anti-fungal, anti-viral, and immunological function activity [4]. In the past, a large number of analytical tools, especially chromatography, have been used to analyze the constituents of TCMs in order to control their quality and discover bioactive compounds. Today, gas chromatography–mass spectrometry (GC–MS), gas chromatography-flame ionization detection (GC–FID), liquid-phase chromatography–mass spectrometry (LC–MS), multi-dimensional liquid chromatography, multi-dimensional gas chromatography, and other chromatographic methods have been developed for TCM analysis [5–12]. Sample preparation is the crucial first step in the chromatographic analysis of TCMs, because it is necessary to extract the desired chemical components from the herbal material. Thus, the development of novel sample-preparation techniques with significant advantages over conventional methods, such as a reduction in organic solvent consumption and in sample degradation, the elimination of additional sample clean-up and concentration steps before chromatographic analysis, improvements in extraction efficiency and selectivity, are likely to play an important role. In 2002, Huie reviewed the sample preparation techniques which had been used for the extraction of medicinal plants [13]. In this paper, more recent developments are reviewed, including headspace solid-phase microextraction (HSSPME), headspace liquid-phase microextraction (HS-LPME), microwave-assisted extraction (MAE), supercritical-fluid extraction (SFE), pressurized-liquid extraction (PLE), and microwave distillation (MD). 2. Sample preparation techniques for TCMs 2.1. Headspace extraction techniques The medicinal properties of TCMs can be partly related to the presence of volatile constituents (e.g. essential oils), and GC–MS and GC–FID are frequently used for their determination. Because the sample to be injected should be free from involatile components, a fractionation step is necessary before analysis. The disadvantages of commonly used samplepreparation techniques, such as steam distillation and liquid solvent extraction, are that they usually require large amounts of organic solvents and manpower. These methods also tend to be destructive in nature and significant artifact formation can occur owing to sample decomposition at high temperatures [14]. Recently, the two techniques of HS-SPME and HS-LPME have been developed for the extraction of volatile constituents from TCMs. 2.1.1. HS-SPME In 1990, Arthur and Pawliszyn [15] introduced a completely solvent-less method, which was termed solid-phase microextraction (SPME), in which a fused silica fiber coated with a stationary phase is exposed to the sample or its headspace and the target analytes partition from the sample matrix to the fiber

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coating [16]. After extracting for a set period of time, the fiber is transferred to the heated injection port of a GC (or GC–MS) for analysis. The method has been applied widely in recent years to the determination of the volatile chemical components of plants and flowers [17–22]. In our early studies [23–26], HS-SPME was successfully applied to the analyses of volatile components in TCMs, including Schisandra chinensis Bail, Chinese arborvitae, Angelico pubescens, and Angelico sinensis. For example, the volatile constituents were extracted from the fruit of S. chinensis (Turz.) Bail using a CW-DVB fiber at 60 ◦ C for 45 min (Fig. 1) and 33 compounds were separated and identified [23]. These studies [23–26] showed that the reproducible and rapid determination of volatile compounds in TCMs could be achieved when HS-SPME was coupled with GC–MS, with the advantages of eliminating the extraction or fractionation step and reducing artifact formation. HS-SPME was also successfully developed as a quality assessment tool for Flos Chrysanthemi Indici from different growing areas [27]. Duan and coworkers developed HS-SPME for the analysis of 35 volatile constituents in Rhioxma Curcumae Aeruginosae [28], and 27 compounds in the TCM prescription of Xiao-Cheng-QiTang [29]. In 2006, Guo and Huang [30] analyzed Atractylodes macrocephala (baizhu) and Atractylodes lancea (cangzhu) by HS-SPME and found 23 common components. The major component extracted from baizhu was atractylone (40.12%) and 36 components representing 90.72% of the total peak area were identified. For cangzhu, the major component was eudesma4,11-diene (16.49%) and 56 components representing 90.38% of the total peak areas were identified. Qi and coworkers analyzed the volatile compounds from Curcuma wenyujin and Houttuynia cotdata by using HS-SPME–GC–MS [31,32]. Compared to steam distillation, HS-SPME was a simple, rapid, and solvent-free sample extraction and concentration technique and has a strong potential for monitoring the quality of TCMs. 2.1.2. HS-LPME In 1996, LPME was introduced by Jeannot and Cantwell [33,34] and He and Lee [35]. This extraction is performed by suspending 1 ␮L drop of organic solvent on the tip of either a Teflon rod or the needle tip of a microsyringe immersed in the stirred aqueous sample. After extraction, the microdrop of organic solvent was injected into a GC–MS. The LPME technique has been applied to environmental analysis and drug analysis [36–40]. In 2001, Theis et al. introduced HS-LPME [41] and demonstrated its application for volatile organic compounds (VOCs) in an aqueous matrix. In 2006, Cao and Qi found similar results by HSLPME and HS-SPME for the analysis of 66 volatile compounds from a common TCM, C. wenyujin (Fig. 2) [42]. HS-SPME and HS-LPME have similar capabilities in terms of precision and speed of analysis and are very suitable for TCM quality assessment but the latter offers two distinct advantages. Firstly, the choice of solvents is wide, compared to the limited number of stationary phases currently available for SPME. Secondly, the cost of the few microliters of solvent is negligible compared to the cost of commercially available SPME fibers.

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Fig. 1. Total ion chromatogram of the volatile constituents of the fruits of Schisandra chinensis (Turz.) Bail by HS-SPME–GC–MS with the fiber of CW-DVB and HS-SPME conditions: 60 ◦ C and 45 min. Reproduced from [23] with permission from Springerlink.

2.2. Microwave-assisted extraction In contrast to conventional liquid–solid extraction methods (e.g. Soxhlet extraction) for which a relatively long extraction time (3–48 h) is required [13,43], the use of microwave energy

for heating the solution results in a significant reduction in the extraction time (usually to less than 30 min). Besides having the advantage of a high extraction speed, MAE also enables a significant reduction in the consumption of organic solvent (typically less than 40 mL, compared with the 100–500 mL required

Fig. 2. GC–MS total ion chromatograms of volatile compounds from C. wenyujin by (a) HS-LPME and (b) HS-SPME. The HS-LPME extraction conditions were: extraction solvent, 0.8 ␮L n-dodecane; extraction temperature, 70 ◦ C; extraction time, 20 min; sample amount, 4.5 g; and sample particle size, 120 mesh. The HSSPME conditions were: 85 ␮m poly-acrylate (PA) fiber; extraction temperature, 80 ◦ C; extraction time, 30 min; sample amount, 1.5 g; and sample particle size, 120 mesh. Reproduced from [42] with permission from Elsevier.

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Fig. 3. The total ion chromatograms of volatile constituents in Rhizoma Curcuma by MAE–HS-SPME–GC–MS. Reproduced from [51] with permission from Elsevier.

for Soxhlet extraction). Recently, MAE was employed for the extraction of flavonoids from Acanthopanax senticosus Harms, Mahonia bealei (Foft.) leaves, and Chrysanthemum morifolium (Ramat.) petals, for rutin and quercetin from Flos Sophorae, and for six ginsenosides from radix ginseng root [44–48]. MAE was also used for the extraction of the water-soluble bioactive constituents (danshensu, puerarin, and ferulic acid) from the traditional Chinese medicinal preparation Tongmaichongji [49]. Recently, Liu et al. employed high-pressure MAE to extract the flavonoids and saponins from A. senticosus leaves [50]. More recently, MAE has been combined with HS-SPME or HS-LPME for the quantitative analysis of volatile active components in TCMs [51–53], including the quantitative analysis of the three important active components curcumol, germacrone, and curdione from Rhizoma Curcuma [51]. The TCM were first extracted with water using MAE (microwave power of 700 W for 4 min). The aqueous extract was extracted with HS-SPME and analyzed by GC–MS (Fig. 3). MAE–HS-SPME was also applied to the determination of camphor and borneol in Flos Chrysanthemi Indici from different growing areas [52] and to the rapid determination of paeonol in Cynanchum paniculatum and Paeonia suffruticosa [53]. This approach provided a simple and rapid and solvent-free tool for the quantitative analysis of active compounds in TCMs. 2.3. Pressurized-liquid extraction Pressurized-liquid extraction emerged in the mid-1990s and Benthin et al. [54] were the first to conduct a comprehensive study on the feasibility of applying PLE to medicinal herbs. The sample in a stainless-steel cell was extracted with an organic solvent at a temperature ranging up to 200 ◦ C under a relatively high pressure, typically 4–20 MPa. Under these conditions, the solubility of the analytes and the mass transfer are increased, and the viscosity and the surface tension of the solvents are decreased, which can improve the contact of the analytes with the solvent and thus enhance the extraction [55]. Recently, Li’s group has applied PLE to TCM analysis [56–66]. They examined the parameters of extraction solvent,

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Fig. 4. CZE profiles of Rhubarb. PLE conditions: the optimum conditions of the PLE method were—solvent, methanol; temperature, 140 ◦ C; particle size, 0.13–0.2 mm; static extraction time, 5 min; pressure, 1500 psi; one extraction. Separation conditions: fused silica capillary (56 cm × 675 mm i.d., 48 cm effective length); pressure injection, 50 mbar for 6 s; running buffer, 50 mM borate buffer (pH 8.2) with 25% acetonitrile and 25% isopropyl alcohol as organic modifier; voltage, 25 kV; temperature, 257 ◦ C; detection at 230 nm. Standards and Rhubarb are shown: (1) physcion; (2) chrysophanol; (3) aloe-emodin; (4) emodin; (5) rhein; IS, 4-methoxysalicyladehyde. Reproduced from [56] with permission from Wiley-VCH.

pressure, temperature, and time for the determination of five anthraquinones, including aloe-emodin, emodin, chrysophanol, physcion, and rhein from Rhubarb before CZE analysis (Fig. 4) [56]. They used PLE followed by GC–MS [57] or HPLC [58] for the identification and quantitative determination of 11 sesquiterpenes, including germacrene D, curzerene, gamma-elemene, furanodienone, curcumol, isocurcumenol, furanodiene, germacrone, curdione, curcumenol, and neocurdione, from Ezhu, which is derived from three species of Curcuma. Li and coworkers applied PLE and HPLC with evaporative light scattering detection to determine 11 major triterpene saponins from Panax notoginseng, which has been known in China for more than 400 years for its efficacy in the treatment of haemoptysis, haemostatic, and haematoma [59–62]. They also developed PLE and HPLC-electrospray ionization tandem mass spectrometry (ESI-MS/MS) method for qualitative and quantitative determination of 43 nucleosides, bases and their analogues in natural and cultured Cordyceps [63]. PLE and HPLC were applied to the determination of Z-ligustilide, Z-butylidenephthalide, and ferulic acid from Angelica sinensis [64], saponins and fatty acids from Suanzaoren [65], and alkaloids and limonoids from Cortex Dictamni [66]. Compared with current methods of Soxhlet extraction, PLE needed only a small sample quantity, and a short extraction time [60,61]. When the temperature of liquid water is raised between 100 and 374 ◦ C under pressure, the polarity decreases markedly and can be used for the pressurized hot water extraction (PHWE) of a wide range of analytes. This technique was a powerful tool for the extraction of essential oils in plant materials by FernandezPerez et al. [67]. In our group, PHWE was successfully combined with HSLPME or HS-SPME, for the volatile active components in

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HPLC and applied it to the analysis of G. lucidum [84] and subsequently expanded this analysis to SFE–LCxLC with atmospheric pressure chemical ionization tandem mass spectrometry [85]. Recently, SFE coupled to high-speed counter-current chromatography (HSCCC) was applied to the analysis of TCMs [86–89]. Peng et al. developed SFE and HSCCC for the extraction and isolation of flavonoids [86,87] and aurentiamide acetate (N-benzoylphenylalaninoylphenylalaninol acetate) from Patrinia villosa Juss [89] and Wang et al. [88] used the technique for the extraction, separation, and purification of psoralen and isopsoralen from Fructus Psoraleae. Today, many active compound are obtained by using SFE–HSCCC technique. 2.5. Microwave distillation Fig. 5. LC chromatogram of the extract from Sinomenium acutum obtained with methanol-modified supercritical carbon dioxide. Reproduced from [80] with permission from Elsevier.

TCMs. Using PHWE–HS-SPME the levels of ␣-asarone in the dry rhizome of the common TCM Acorus Tatarinowii Schott from three different growing areas was quantitatively analyzed [68]. Using GC–MS following PHWE and HS-SPME, the active constituents, such as Z-ligustilide and E-ligustilide, from Ligusticum chuanxiong and A. sinensis were determined [69,70]. PHWE–HS-LPME followed by GC–MS was developed for analysis of volatile active compounds such as Fructus amomi [71,72]. It has been shown that PHWE requires only a short time to prepare the sample, and uses only a small sample size and no organic solvent. 2.4. Supercritical-fluid extraction Supercritical-fluid extraction has been used for many years for the extraction of volatile components, such as essential oils and aroma compounds, from plant materials, on a laboratory and industrial scale [73,74]. The advantages include the ability to perform rapid (often less than 30 min) extractions, to reduce the use of hazardous solvents because carbon dioxide is commonly used as the extraction solvent, and to couple the extraction step with gas, liquid, or supercritical-fluid chromatography. An important aspect of applying SFE to the extraction of active compounds from TCMs is that potential degradation as a result of a lengthy exposure to elevated temperatures and atmospheric oxygen are avoided. Supercritical carbon dioxide extraction was used to extract the essential oil for GC–MS from Aloe vera [75], Polygonum cuspidatum [76], radix Angelicae dahuricae [77], ginger [78], and Cinnamomum cassia presl [79]. Liu et al. used SFE with methanol-modified supercritical carbon dioxide, followed by LC for the analysis of sinomenine from Sinomenium acutum (Fig. 5) [80]. The same method was also applied to the analysis of berberine from rhizome of Coptis chinensis Franch [81], triterpenoids in fruiting bodies of Ganoderma lucidum [82], and saponins from Ginseng [83]. Zhang et al. coupled SFE with

In 2003, Chemat et al. invented the novel technique of microwave distillation (MD) [90], which is a combination of microwave heating and dry distillation at atmospheric pressure. MD was conceived for the laboratory scale extraction of essential oils from aromatic plants. Based on a relatively simple idea, MD involves placing plant material in a microwave reactor, without any added solvent or water. The internal heating of the water within the plant material distends the plant cells and leads to rupture of the glands and oleiferous receptacles. This frees essential oils which are evaporated by the water of the plant material. A cooling system outside the microwave oven condenses the distillate. The excess of water was refluxed to the extraction vessel in order to restore the water to the plant material. Lucchesi et al. compared the MD technique with a conventional hydro-distillation for extraction of essential oils from aerial parts of three aromatic herbs: basil (Ocimum basilicum L.), garden mint (Mentha crispa L.), thyme (Thymus vulgaris L.) [91] and showed that the MD method offers important advantages over traditional alternatives, namely: shorter extraction times (30 min for MD method against 4.5 h for hydro-distillation), substantial savings of energy, and a reduced environmental burden (less CO2 released into the atmosphere). Recently, Wang et al. used the MD technique for the extraction of essential oils from Cuminum cyminum L. and Zanthoxylum bungeanum

Fig. 6. GC–MS total ion chromatograms of essential oils extracted from Cuminum cyminum L. by microwave distillation (a, microwave power of 85 W, extraction time of 30 min) and steam distillation (b, distillation time of 180 min). Reproduced from [92] with permission from Elsevier.

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Table 1 Comparison of the sample preparation techniques for TCM Sample techniques

Extraction constituents

Organic solvent

Extraction time (min)

Sample amount (g)

Special equipment

Quantitative analysis

HS-SPME HS-LPME MD MAE PLE SFE

VC VC VC VC and NVC VC and NVC VC and NVC

NR NR NR R R NR

15–60 15–60 30–60 30–120 5–30 120–240

1–5 1–5 20–40 5–40 0.5–5 20–40

NR NR R R R R

SAQ SQA QA QA QA QA

VC, volatile constituents; NVC, non-volatile constituents; NR, no requirement; R, requirement; SQA, semi-quantitative analysis; QA, quantitative analysis.

Maxim [92]. In their method, carbonyl iron powders (CIP) were used as the microwave absorption solid medium mixed with the TCM. Similar compounds were found when the extract was compared with a conventional steam distillation (Fig. 6) but the MD required only 30 min compared to 180 min for steam distillation. MD combined with headspace techniques, such as HS-SPME and HS-LPME, had been used the extraction and concentration of volatile compounds from TCMs [93–95] using a short analysis time and no solvent. 3. Conclusions The six new sampling techniques for TCMs have been compared (Table 1). HS-SPME and HS-LPME require no special equipment or organic solvent and are easy to use and low cost but only extract volatile constituents and only a semi-quantitative analysis can be obtained. MD is an inexpensive, fast, simple, and organic-free sample technique for TCM volatile oils and SFE, MAE, and PLE seem to offer a good approach for the extraction of volatile and non-volatile constituents. The three sample techniques combined with GC or HPLC are good choice for quantitative analysis of active compounds in TCMs. Acknowledgements The work was supported by grants from National Basic Research Priorities Programme (Project No. 2001CB510202), Shanghai Basic Research Priorities Programme (No. 05dz19741) and Natural Science Foundation of China (Project No. 39870451). References [1] K. Chen, Trends Pharmacol. Sci. 16 (1995) 182. [2] Y.Z. Chen, S.Y. Chen, Introduction of Chemical Methods in Study of Modernization of Traditional Chinese Medicines, Science Publishing, Beijing, China, 2003, p. 1. [3] Pharmacopoeia of People’s Republic of China, 2000th ed., Chemical Industry Publishing, 2000. [4] T.H. Tsai, J. Chromatogr. B 764 (2001) 27. [5] X.D. Huang, L. Kong, H.F. Zou, J. Chromatogr. B 812 (2004) 71. [6] J.J. Ou, L. Kong, C.S. Pan, X.Y. Su, X.Y. Lei, H.F. Zou, J. Chromatogr. A 1117 (2006) 163. [7] X.G. Chen, L.H. Hu, H.F. Zou, J. Pharm. Biomed. Anal. 40 (2006) 559. [8] L.H. Hu, X.G. Chen, L. Kong, H.F. Zou, J. Chromatogr. A 1092 (2005) 191. [9] S. Ma, L.X. Chen, G.A. Luo, K.N. Ren, J.F. Wu, Y.M. Wang, J. Chromatogr. A 1127 (2006) 207.

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