Preconcentration and Determination of Nickel (II) and Copper (II) Ions, in Vegetable Oils by [TBP] [PO4] IL-Based Dispersive Liquid–Liquid Microextraction Technique, and Flame Atomic Absorption Spectrophotometry

Journal Pre-proof Preconcentration and Determination of Nickel (II) and Copper (II) Ions, in Vegetable Oils by [TBP] [PO4 ] IL-Based Dispersive Liquid–Liquid Microextraction Technique, and Flame Atomic Absorption Spectrophotometry Khavar Adhami (Investigation) (Data curation) (Formal analysis) (Writing - original draft) (Validation), Hamideh Asadollahzadeh (Project administration) (Conceptualization) (Methodology) (Software) (Writing - review and editing) (Supervision), Mahdieh GhazizadehWriting - review and editing, Supervision) (Software)

PII:

S0889-1575(19)31235-9

DOI:

https://doi.org/10.1016/j.jfca.2020.103457

Reference:

YJFCA 103457

To appear in:

Journal of Food Composition and Analysis

Received Date:

20 August 2019

Revised Date:

11 January 2020

Accepted Date:

17 February 2020

Please cite this article as: Adhami K, Asadollahzadeh H, Ghazizadeh M, Preconcentration and Determination of Nickel (II) and Copper (II) Ions, in Vegetable Oils by [TBP] [PO4 ] IL-Based Dispersive Liquid–Liquid Microextraction Technique, and Flame Atomic Absorption Spectrophotometry, Journal of Food Composition and Analysis (2020), doi: https://doi.org/10.1016/j.jfca.2020.103457

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Preconcentration and Determination of Nickel (II) and Copper (II) Ions, in Vegetable Oils by [TBP] [PO4] IL-Based Dispersive Liquid–Liquid Microextraction Technique, and Flame Atomic Absorption Spectrophotometry

Khavar Adhamia, Hamideh Asadollahzadeha*, Mahdieh Ghazizadeha a

Department of Chemistry, Kerman Branch, Islamic Azad University, Kerman 7635131167,

Iran. *

Corresponding

author:

Hamideh

Asadollahzadeh.

Email

address:

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[email protected]

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Graphical Abstract

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Highlights

 Determining of Ni2+ and Cu2+ ions, in vegetable oils by method of [TBP] [PO4] IL-based dispersive liquid–liquid microextraction technique, by flame atomic absorption spectrophotometry.  Enrichment and determination of traces of Ni2+ and Cu2+ ions, in vegetable oils by [TBP] [PO4] IL.

 *Use of a green solvent in IL-DLLME method for preconcentration of Ni2+ and Cu2+ ions in vegetable oils. Abstract The present research is a novel enrichment method based on ionic liquid dispersive liquidliquid micro-extraction that was combined with flame atomic absorption spectroscopy to determine the concentration of Cu2+ and Ni2+ ions in vegetable oil samples at trace levels. The ionic liquid [TBP] [PO4] and chloroform were used as the extraction and dispersive solvent respectively. Canola oil containing oil-soluble standard of Cu2+ or Ni2+ ions as the model

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compound was used. Under optimum conditions the linear ranges were 1-100 and 1-200 μg/kg for Cu2+ and Ni2+ respectively with correlation coefficient (R2) of 0.99. The relative standard deviation (RSD, n = 5) for Cu2+ and Ni2+ at a concentration of 20 μg/kg was 2.2% and 3.2% respectively. The LOD (3s) and LOQ (10s) were 0.35 ppb and 1.2 ppb; and 0.77 ppb and 2.57

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ppb for Cu2+ and Ni2+ respectively.

Keywords: Metal ions preconcentration, tetrabutyl phosphonium phosphate ionic liquid, IL-

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1. Introduction

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DLLME, Vegetable oils.

Vegetable oils are widely utilized in cooking and alimentary, cosmetics, pharmaceutical and chemical industries (Sobhanardakani, 2016). The quality of edible oils regarding their

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freshness, storability and toxicity may be evaluated by determination of several trace metals which are the most important factors in decreasing the shelf life of commercial products

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(Farzin, Moassesi, 2014). These metals could come from the soil, environment and genotype of the plant, fertilisers and metal-containing pesticides, through the production process or by contamination from the metal processing equipment (Zhu et al., 2011; Gunduz et al., 2015).

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The development of rapid and accurate analytical methods for the determination of metal concentrations in edible oils is essential when it comes to quality control and food analysis (Ansari et al., 2009; Ieggli et al., 2011; Burguera et al., 2012). In the literature, there are lots of studies on the determination of trace elements in edible oils and their controls for the human health using different sample preparation procedures such as wet digestion, microwave-assisted digestion, ashing, emulsion and etc. (Ansari et al., 2009; Lepri et al., 2011; Ieggli et al., 2011). In digestion or ashing procedures, some losses and/or

contamination may occur and may not be reproducible, causing inaccurate results. In addition, these procedures are quite dangerous, expensive (microwave assisted digestion) and not ecofriendly due to high acid consumption and etc. In emulsion method, the forming of an emulsion of the oil/fat samples, with the assistance of emulsifying agents, is an option to pre-treatment because it does not require the decomposition of the organic matrix and supplies a rapid process of sample preparation (Kilinc et al., 2009). The key problem when utilizing emulsions arises in maintaining their stability for a suitable period of time (Burguera et al., 2012). The trace elements level in samples to be analysed is sometimes less than the detection limit of analytical instruments such as flame atomic absorption spectroscopy (FAAS), inductively

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coupled plasma optical emission spectrometry (ICP OES) and graphite furnace-atomic absorption spectrometry (GF-AAS) (Yao et al., 2018 ). Therefore, a suitable sample pretreatment step is really a required step before the analysis. In addition, it is not appropriate to introduce the oils directly to the flame or graphite furnace of AAS as well as to the plasma of inductively coupled plasma (ICP) due to problems linked to aspiration and injection of samples,

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atomization yields of oil drops, calibration against aqueous standards and etc. Therefore,

(Burguera et al., 2012; Yao et al., 2018).

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sampling has been made after various pre-treatments of samples prior to measurement Dispersive liquid-liquid micro extraction (DLLME) overcomes a number of the drawbacks of

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old sample preparation techniques (Campillo et al., 2015; Martınez et al., 2018; Sixto et al., 2019). It is simple, fast, and does not require large amounts of organic solvents and is applicable to separation, preconcentration and determination of organic and inorganic compounds in

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different samples (Biparva et al., 2012; Pereira et al., 2013; Soleiman, Zakerian, 2014; Farajzadeh et al., 2019).

Recently, the application of ionic liquids (ILs) as solvents in place of organic solvents, in

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conjunction with various techniques has attracted considerable attention in the field of analytical chemistry (Sun, Armstrong, 2010). Room temperature ionic liquids (RTIL) represent

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a novel medium that is composed entirely of ions (Trujillo-Rodriguez et al., 2013; Aslam Arain et al., 2016; Fan et al., 2017; Magiera, Sobik, 2017; Zare-Shahabadi et al., 2017). They are generally regarded as being environmentally friendlier than common organic solvents and have unique chemical and physical properties such as negligible vapour pressure, non-flammability, good extractability for various organic compounds and metal ions as neutral or charged complexes, along with tuneable viscosity and miscibility with water and organic solvents (Moalla, Amin, 2015).

In the literature, ionic liquid-based dispersive liquid–liquid microextraction technique (ILDLLME) was used to determine traces of metals such as Ni, Cu, and Zn in waste water, water, alloy and human serum samples (Stanisz et al., 2014; AslamArain et al., 2016; Zare-Shahabadi et al., 2017) by flame-AAS. The present study applied a new approach to optimize IL-DLLME-FAAS conditions for the extraction and determination of Cu2+ and Ni2+ ions in vegetable oil samples by using tetra butyl phosphonium phosphate ionic liquid ([TBP] [PO4] IL). The effects of various experimental parameters, such as the kind and volume of dispersive solvent, amount of extraction solvent, extraction time, centrifugation time and temperature of extraction were studied and optimized.

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Using the developed method, these ions can be analysed in vegetable oil samples in a simpler, cheaper and more rapid manner.

2. EXPERIMENTAL

2.1. Instrumentation

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The measurement was performed with a Shimadzu atomic absorption spectrometer (AA-670) equipped with a gas controller, graphic printere and deuterium background correction. Hollow

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cathode lamps of copper and nickel operating at 3 and 4 mA were utilized respectively as the radiation sources. The analytical wavelengths (324.8 and 232.0 nm) and slit widths (0.5 and

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0.15 nm) and air-acetylene flame with a fuel-oxidant ratio of 1.8:8 and 1.7: 8 for copper and nickel were used respectively. A laboratory centrifuge (Romisa 4500, Eskantara, Iran) was used to accelerate the phase separation. IR spectra (4000–400 cm–1) were recorded with

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diamond ATR probe, using Bruker FT–IR (Tensor) spectrophotometer. 1H NMR analysis was done using Bruker Spectrospin 300. The CHN element analyser (ECS 4010, Costech, Italy)

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and a Karl Fischer moisture titrator (MKV-710, Kem, Japan) were used.

2.2. Reagents and standard solutions

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All reagents used were of analytical reagent grade. Chloroform, acetone, acetonitrile (ACN), phosphoric acid 85%, Ethyl alcohol 95%, Cu2+ and Ni2+ stock aqueous standard solutions of 1000.0 mg/L were purchased from Merck (Darmstadt, Germany). Tetrabutyl phosphonium hydroxide [TBP] [OH] (40% by mass aqueous solution) was purchased from Sigma Aldrich. Cu2+, Pb2+, Fe2+, Cd+2, Mn+2 and Ni2+ oil-based standards, 1000 µg/g, were purchased from Alfa Aesar. Ultra-pure distilled water (DRO.Di50 LS, Aban Group, Iran) was used during the study. Solutions of lower concentrations were prepared on a daily basis by a suitable dilution

of the stock solution with distilled water for aqueous standards and chloroform for oil-based standards. Sunflower and canola oils were obtained from deodorization stage of Golnaz vegetable oil Company (Kerman, Iran) and delivered to the company’s laboratory and stored at a dry and cool place far from sunlight. Vessels in the experiments were kept in 10% nitric acid for at least 24 h and were washed with the ultra-pure distilled water. 2.3. Synthesis of the ionic liquid Tetrabutyl phosphonium phosphate ionic liquid ([TBP] [PO4] IL) was synthesized in Golnaz laboratory according to the previously reported method (Adhami et al., 2019). Briefly, the IL was prepared by mixing equimolar amounts of an aqueous solution of the phosphoric acid and

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tetrabutyl phosphonium hydroxide. After the reaction was done, the solution was placed on a rotary evaporator at 80 °C under magnetic stirrer set at 300 rpm to remove the water, and final traces of water were removed by heating (50-60 °C) under vacuum (0.1Pa) for 3 days. To ensure the purity of the IL, it was dissolved in acetonitrile and was treated with activated

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charcoal for at least 24 h, and finally after filtering, acetonitrile was evaporated in vacuo. The structure and purity of the IL was checked by 1H NMR, FT–IR and CHN element analyser. The

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water content of the IL was checked by Karl Fischer moisture titrator, which was less than 1 wt%.

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2.4. Dispersive liquid-liquid micro extraction procedure by [TBP] [PO4] ionic liquid Aliquots of 5.0 g of the refined canola oil containing 140 μg/kg Ni2+ or 60 μg/kg Cu2+ oil- based standard were weighted in a 10 mL test tube with conical bottom. Then, 2 mL chloroform

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(dispersive solvent) containing 50 mg [TBP] [PO4] IL (extraction solvent) was injected rapidly into the sample oil (refined canola) by a 5.0 mL glass syringe. After 10 min, the mixture was centrifuged for 10 min at 4000 rpm. The upper layer (oil phase) was removed and the bottom

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layer (IL phase) was allowed so that residue of solvent (chloroform) evaporates in water bath at 70 ± 5 °C for 10 ± 2 min and then the residue was diluted in 2 mL double distilled water and

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the ions absorbance were determined by flame atomic absorption spectrometry. At least three repetitive experiments were performed and all experiments included blank samples.

3. Result and discussion In this work, IL- DLLME method was combined with flame atomic absorption spectroscopy to determine the concentration of Cu2+ and Ni2+ ions in vegetable oil samples at trace levels. For this work, the effect of several factors influencing the extraction conditions were investigated and optimized.

3.1. Selection of diluting agent Based on FAAS, the solvent should have good nebulization and burning characteristics, compatibility with direct injection into FAAS and not have a very low-boiling point. To dilute the sedimented IL phase at the bottom of the tube, 2 mL of distilled water, ethanol and acetonitrile were studied. All of these solvents could dissolve the sedimented IL phase, but acetonitrile dissolved better. However, distilled water was chosen due to major compatibility of distilled water with flame atomic absorption spectroscopy.

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3.2. Effect of the amount of [TBP] [PO4] IL (extraction solvent) The effect of amount of the IL was studied at the range of 10-400 mg. In this research, the amount of dispersive solvent (chloroform) was 2 mL. The minimum amount of the IL required for the formation of cloudy solution was 10 mg. By increasing the IL amount, the absorbance of Cu2+ and Ni2+ ions initially increased up to about 50 mg and then began to decrease (Fig. 1)

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because of an increase in the amount of settled IL phase. By increasing the amount of the settled IL phase, viscosity of the IL- water mixture increases. When the viscosity of solution aspirated

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into the flame of the atomic absorption spectrophotometer increased, the nebulization was insufficient and therefore the absorbance decreased. Therefore, 50 mg of the [TBP] [PO4] IL

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was chosen as the optimum value.

3.3. Effect of type and volume of the dispersive solvent

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A dispersive solvent was chosen based on dissolving both the IL phase and the oil sample. Thus acetone, ethanol, n-hexane, isooctane and chloroform were investigated, and finally chloroform was chosen. In other words, the volume of dispersive solvent directly affected the

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IL solubility in the oil phase which significantly determined the volume of the final phase and thus influenced the efficiency of the micro extraction technique. Therefore, chloroform

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volumes ranging within 0.5, 1, 2, 3 and 4 mL were assayed (Fig. 2). Using low volume of chloroform (<0.5mL), the cloudy state of solution was not formed completely. At high volumes of chloroform (>3mL), the absorbance decreased. Thereby, 2 mL was chosen as optimum volume of dispersive solvent.

3.4. Effect of extraction time

In DLLME, the extraction time is defined as the time taken between injecting and centrifugation (Al-Saidi, Emara, 2014). In this study, the effect of extraction time on the absorbance was studied at 2, 5, 10, 15 and 20 min time ranges. As shown in Fig. 3, the optimum extraction time was 10 min.

3.5. Effect of centrifuge time The effect of centrifugation time on the absorbance was studied at 5, 10, 15, 20 and 25 min time ranges. The optimum centrifugation time was considered 10 min because complete extraction occurred at this time and no appreciable improvements were observed for longer

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times (Fig. 4).

3.6. Effect of extraction temperature

The effect of extraction temperature on the absorbance was studied at 15, 25, 40 and 60 °C and

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the maximum absorbance of Cu2+ and Ni2+ ions was in 25 °C (Fig. 5). Since the IL remains disperse in oil at high temperatures but is easily settled in room temperature and because at low temperature oil becomes viscous, the dispersive solvent will not be in complete contact with

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analyte and less of that enters the extraction solvent. As a result, the absorbance of these ions

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decreases.

3.7. Effects of foreign ions on the absorbance

In the current study, [TBP] [PO4] IL was used as an extraction solvent for Cu2+ and Ni2+ ions

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in the vegetable oil samples. It can also react with other metal ions and may interfere in extraction of the analytes. Thus, the effects of various co-existing ions (Fe2+, Pb2+, Ni2+, Cd+2,

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Mn+2 and Cu2+) in the vegetable oil samples on the absorbance of Cu2+ and Ni2+ ions were

studied. For this purpose, a concentration of 50 µg/kg Cu2+ and Ni2+ in canola oil were investigated. The tolerance limit is defined as the largest amount of interfering ions causing a

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relative error ≤ 5% related to the preconcentration and determination of Cu2+ and Ni2+ ions. These tolerance limits are shown in Table 1.

3.8. Evaluation of method performance In this study, it was shown that the calibration curves were linear in the concentration range of 1-100 and 1-200 μg/kg with correlation coefficient (R2) of 0.99 for Cu2+ and Ni2+ respectively. The limits of detection (LOD) and quantification (LOQ) were calculated as three and ten times

the standard deviation of ten measurements of a blank divided by the slope of the calibration graph. The LOD and LOQ were 0.35 and 1.2 ppb; 0.77 and 2.57 ppb for Cu2+ and Ni2+ respectively. The enhancement factors (EF) were obtained 63 and 158 for Ni2+ and Cu2+ respectively and were calculated by the following equation (Zare-Shahabadi et al., 2017): EF =

C2 C1

Where C2 and C1 are the concentrations of analyte in the ionic liquid phase and in the refined canola oil samples before extraction, respectively. Also, by finding the slope ratios (m2/m1) of calibration curve with extraction method and without extraction method, enhancement factors were obtained 65 for Ni2+ and 163 for Cu2+. The relative standard deviation (RSD) from the

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analysis of five replicates of the 5 g refined canola oil sample, containing 20 μg/kg Cu2+, and 20 μg/kg Ni2+, were found 2.2% and 3.2% for Cu2+ and Ni2+ respectively.

To validate this method, two methods (current and ashing methods) were compared. For this purpose, 20μg of oil-based standards of Cu2+ or Ni2+ ions was added to 5 g of refined canola

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oil and was ashed according to procedure (Sahu et al., 2016) and finally the concentrations of Cu2+ and Ni2+ ions were determined by FAAS. And then 20 μg of oil-based standards of Cu2+

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or Ni2+ ions was added to 5 g of refined canola oils and current method was performed and concentrations of Cu2+ and Ni2+ ions were determined by FAAS. After that, F-test and T-test

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were performed. The results showed that the f and t experimental are less than f and t critical. The results are shown in Table 2 and 3.

Also the characteristic data of the present method were compared with emulsion (Ieggli et al.,

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2011) and microwave-assisted acid digestion methods (Farzin, Moassesi, 2014). The LOD and LOQ for Cu2+ are 20 ppb and 61 ppb in emulsion method and 0.62 ppb and 2.04 ppb in microwave-assisted acid digestion method and for Ni2+ are 13 and 36 ppb in emulsion method

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and 0.45 ppb and 1.49 ppb in microwave-assisted acid digestion method respectively. The

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results are shown in Table 4.

3.9. Analysis of real samples In order to validate the proposed method, it was applied to the determination of Cu2+ and Ni2+ in refined sunflower, and canola oil samples. Before the analysis of real samples, they were stirred until homogeneous. If the samples had suspended solids, they were filtered and 5 g of each sample was pre-concentrated using the [TBP] [PO4] IL-DLLME method under optimum condition. The results are shown in Table 5. In all cases, the spike recoveries confirmed the

reliability of the proposed method. As is seen, the mean recovery values were 88.2% and 93.3% for Ni2+ and Cu2+ respectively.

4. CONCLUSIONS In this study, an ionic liquid-based dispersive liquid-liquid micro-extraction method ([TBP] [PO4] IL-DLLME-FAAS) was developed for the pre-concentration and determination of Cu2+ and Ni2+ ions from vegetable oil samples. This method is simple, rapid and inexpensive and has high enrichment factors for Cu2+ and Ni2+ ions. Since this method preconcentrates and enriches the analytes, it is suitable for low limit detection of these ions in vegetable oils. Also

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this is a good approach in terms of green chemistry because of using [TBP] [PO4] IL as a green extraction solvent.

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Author statement

Hamideh asadollahzadeh: Project administration, Conceptualization, Methodology,

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Software, Writing- Reviewing and Editing, Supervision

Khavar Adhami: Investigation, Data curation, Formal analysis, Writing- Original draft

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preparation, Validation

Acknowledgment

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Mahdieh Ghazizadeh: Writing- Reviewing and Editing, Supervision, Software

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The authors are grateful to Islamic Azad University, Kerman Branch, for financial assistance of this work. Also, the authors are grateful to the Board of Directors of Golnaz Vegetable Oil Company for

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their full support of the research.

References Adhami Kh., Asadollahzadeh H., Ghazizadeh M. (2019). A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutyl phosphonium phosphate ionic liquid. Journal of Industrial and Engineering Chemistry 76, 245-250. Al-Saidi H.M., Emara A. A. A. (2014). The recent developments in dispersive liquid–liquid microextraction for preconcentration and determination of inorganic analytes. Journal of Saudi Chemical Society 18, 745-761. Ansari R., Kazi T. G., Jamali M. K., Arain M. B., Wagan M.D., Jalbani N., Afridi H. I.,

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Shah A.Q. (2009) Variation in accumulation of heavy metals in different verities of sunflower seed oil with the aid of multivariate technique. Food Chemistry 115, 318323.

AslamArain S., GulKazi T., Afridi H.I., Shahzadi Arain M., Haleem Panhwar A., Khan N.,

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Ahmed Baig J., Shah F. (2016). A new, dispersive liquid–liquid micro extraction using ionic liquid based micro emulsion coupled with cloud point extraction for

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determination of copper in serum and water samples. Ecotoxicology and Environmental Safety 126, 186-192.

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Biparva P., Ehsani M., Hadjmohammadi M. R. (2012). Dispersive liquid–liquid microextraction using extraction solvents lighter than water combined with high performance liquid chromatography for determination of synthetic antioxidants in

na

fruit juice samples. Journal of Food Composition and Analysis 27, 87-94. Burguera J.L., Burguera M. (2012). Analytical applications of emulsions and micro

ur

emulsions. Talanta 96, 11-20. Campillo N., Viñas P., Férez-Melgarejo G., Hernández-Córdoba M. (2015) Dispersive

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liquid-liquid micro extraction for the determination of flavonoid aglycone compounds in honey using liquid chromatography with diode array detection and time-of-flight mass spectrometry. Talanta 131, 185-191.

Fan Y., Xu C.H., Wang R., Hu G., Miao J., Hai K., Lin C.H. (2017). Determination of copper (II) ion in food using an ionic liquids-carbon nanotubes-based ion-selective electrode. Journal of Food Composition and Analysis 62, 63-68.

Farajzadeh M.A., Nasiri H. (2019). Picoline based - homogeneous liquid-liquid micro extraction of cobalt (II) and nickel (II) at trace levels from high volume of aqueous sample. Analytical Methods 10, 1379-1386. Farzin L., Moassesi M.E. (2014). Determination of Metal Contents in Edible Vegetable Oils Produced in Iran Using Microwave-assisted Acid Digestion. Journal of Applied Chemical Research 8, 35-43. Gunduz S., Akman S. (2015). Investigation of trace element contents in edible oils sold in Turkey using micro emulsion and emulsion procedures by Graphite furnace atomic absorption spectrophotometry. LWT - Food Science and Technology 64, 1329-1333.

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Ieggli C.V., Bohrer D., Do Nascimento P.C., De Carvalho L.M. (2011). Flame and graphite furnace atomic absorption spectrometry for trace element determination in vegetable oils, margarine and butter after sample emulsification, Food Additives & Contaminants: Part A. 5, 640-648.

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Kilinc E., Lepane V., Viitak A., Gumgum B. (2009). Off-line determination of trace silver in water samples and standard reference materials by cloud point extraction-atomic

re

absorption spectrometry. Proceedings of the Estonian Academy of Sciences 58, 190-196.

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Lepri F., Chaves E., Vieira M., Riberio A., Curtius A., Deoliveira L. (2011). Determination of trace elements in vegetable oils and biodiesel by atomic spectrometric

na

techniques A review. Applied Spectroscopy Reviews 46, 175-206. Magiera S., Sobik A. (2017) Ionic liquid-based ultrasound-assisted extraction coupled with liquid chromatography to determine isoflavones in soy foods. Journal of Food

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Composition and Analysis 57, 94-101. Martınez D., Grindlay G., Gras L., Mora J. (2018). Determination of cadmium and lead in

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wine samples by means of dispersive liquid-liquid microextraction coupled to electrothermal atomic absorption spectrometry. Journal of Food Composition and Analysis 67, 178-183.

Moalla S.M.N, Amin A.S. (2015). An ionic liquid-based micro extraction method for highly selective and sensitive trace determination of nickel in environmental and biological samples. Analytical Methods 7, 10229-10237.

Pereira E.R, Soares B.M, Maciel J.V, Caldas S.S, Andrade C.F.F., Primel E.G, Duarte F.A. (2013). Development of a dispersive liquid–liquid microextraction method for iron extraction and preconcentration in water samples with different salinities. Analytical Methods 5, 2273-2280. Sixto A., Mollo A., Knochen M. (2019). Fast and simple method using DLLME and FAAS for the determination of trace cadmium in honey. Journal of Food Composition and Analysis 82, 103229. Sobhan ardakani S., (2016) Health risk assessment of As and Zn in canola and soybean oils. Journal of Advances in Environmental Health Research 4(2), 62-67.

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Soleiman B., Zakerian R. (2014). Ionic liquid based dispersive liquid liquid Microextraction and enhanced determination of the Palladium in water, soil and vegetable samples by FAAS. Iranian Journal of Chemistry and Chemical Engineering 4, 51-58.

Stanisz E., Werner J., Zgoła-Grzes´kowiak A. (2014). Liquid-phase microextraction

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Trends in Analytical Chemistry 61, 54–66.

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techniques based on ionic liquids for preconcentration and determination of metals.

Sun P., Armstrong D.W. (2010). Ionic Liquids in Analytical Chemistry. Analytica Chimica

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Acta 661, 1-16.

Trujillo-Rodriguez M.J., Rocio-Bautista P., Pino V., Afonso A.M. (2013). Ionic liquids in dispersive liquid-liquid micro extraction, Trends in Analytical Chemistry 51, 87-106.

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Yao L., Liu H., Wang X., Xu W., Zhu Y., Wang H., Pang L., Lin C.H. (2018). Ultrasoundassisted surfactant-enhanced emulsification microextraction using a magnetic ionic

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liquid coupled with micro-solid phase extraction for the determination of cadmium and lead in edible vegetable oils. Food Chemistry, 256, 212-218.

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Zare-Shahabadi V., Asaadi P., Abbasitabar F., Shirmardi A. (2017). Determination of Traces of Ni, Cu, and Zn in Wastewater and Alloy Samples by Flame-AAS after Ionic Liquid-Based Dispersive Liquid Phase Micro extraction. Journal of the Brazilian Chemical Society 5, 887-894.

Zhu F., Fan W., Wang X., Qu L., Yao S.h., (2011). Health risk assessment of eight heavy metals in nine varieties of edible vegetable oils consumed in China. Food and Chemical Toxicology 49, 3081-3085.

Figure captions

Fig.1. Effect of amount of [TBP] [PO4] ionic liquid on the absorbance. Conditions: amount of refined canola oil samples: 5 g, dispersive solvent (chloroform): 2 mL, concentration of Ni2+ and Cu2+: 140 µg/kg and 60 µg/kg (in refined canola oil) respectively, extraction and centrifugation time: 10 min, temperature of extraction: ambient temperature. Values are means ± SD, n ≥ 3

Fig.2. Effect of volume of dispersive solvent (chloroform) on the absorbance. Conditions: amount of refined canola oil samples: 5 g, amount of [TBP] [PO4] ionic liquid: 50 mg,

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concentration of Ni2+ and Cu2+:140 µg/kg and 60 µg/kg (in refined canola oil) respectively, extraction and centrifugation time: 10 min, temperature of extraction: ambient temperature. Values are means ± SD, n ≥ 3

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Fig.3. Effect of extraction time on the absorbance. Conditions: amount of refined canola oil samples: 5 g, amount of [TBP] [PO4] ionic liquid: 50 mg, dispersive solvent (chloroform): 2

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mL, concentration of Ni2+ and Cu2+: 140 µg/kg and 60 µg/kg (in refined canola oil) respectively, centrifugation time: 10 min, temperature of extraction: ambient temperature.

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Values are means ± SD, n ≥ 3

Fig.4. Effect of Centrifugation time on the absorbance. Conditions: amount of refined canola

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oil samples: 5 g, amount of [TBP] [PO4] ionic liquid: 50 mg, dispersive solvent (chloroform): 2 mL, concentration of Ni2+ and Cu2+: 140 µg/kg and 60 µg/kg (in refined canola oil) respectively, extraction time: 10 min, temperature of extraction: ambient temperature. Values

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are means ± SD, n ≥ 3

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Fig. 5. Effect of extraction temperature on the absorbance. Conditions: amount of refined canola oil samples: 5 g, amount of [TBP] [PO4] ionic liquid: 50 mg, dispersive solvent (chloroform): 2 mL, concentration of Ni2+ and Cu2+: 140 µg/kg and 60 µg/kg (in refined canola oil) respectively, extraction and centrifugation time: 10 min. Values are means ± SD, n ≥ 3

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Fig. 1.

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Fig.2.

Ni

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Cu

1

Abs

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0.8 0.6

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0.4

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0.2 0

0

5

10

15

Extraction time (min) Fig. 3.

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Fig. 5.

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Table 1: Effects of foreign ions on the absorbance of 50 µg/kg of Cu2+ and Ni2+in oil sample (canola) by [TBP] [PO4] IL-DLLME-FAAS. Coexisting ions

Tolerance ratio C ion/C Ni2+

Cu2+

-

1000 *

Ni2+

1000 *

-

Fe2+

1000 *

10000 *

Pb2+

1000 *

10000 *

Cd+2

800*

450*

Mn+2

900*

700*

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C ion/C Cu2+

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-p

*At this ratio interfering effect was observed.

Table 2 comparing of ashing method with this method ([TBP] [PO4] IL-DLLME-FAAS) for

lP

determination of Cu2+ after adding 20 μg of oil-based standard of Cu2+ ions to 5g refined canola oils.

*Ashing

na

Concentration of Cu2+

Method

Xa

Sb

TcCrit.

TExp.

FCrit.

FExp.

18.10±0.80

18.85±0.46

19.10±0.61

20.86±0.37

19.23

1.17

This work 17.75±0.60

18.30±0.34

19.15±0.27

18.95±0.23

18.54

0.64 1.943 1.035 9.277 3.342

ur

*(conventional method in Golnaz vegetable oil company laboratory) (mean)

b

(standard deviation)

Jo

a

c

(confidence level 95%)

Table 3 comparing of ashing method with this method ([TBP] [PO4] IL-DLLME-FAAS) for determination of Ni2+ after adding 20 μg of oil-based standard of Ni2+ ions to 5g refined canola oils. Concentration of Ni2+

Method *Ashing

17.50±0.70

18.65±0.46 18.70±0.61

This work 17.55±0.40

21.0±0.37

Xa

Sb

18.96

1.47

18.11±0.37 18.85±0.73 19.35±0.60 18.47

TcCrit.

TExp.

FCrit.

FExp.

0.79 1.943 0.587 9.277

3.46

*(conventional method in Golnaz vegetable oil company laboratory) a (means) b (standard deviation)

-p

ro of

c (confidence level 95%)

Linear range (ppb)

re

Table 4 Comparison of analytical parameters of this method ([TBP] [PO4] IL-DLLMEFAAS) and emulsion, microwave-assisted acid digestion methods. LOD (ppb)

Cu2+

Ni2+

This work

1-100

1-200

0.35

Emulsion

0-40

0-40

Microwaveassisted Acid Digestion

-

-

na

ur Jo

Cu2+

Ni2+

RSD%

References

Cu2+

Ni2+

Cu2+

Ni2+

0.77

1.2

2.57

2.2

3.2

-

20

13

61

36

-

--

Ieggli et al. 2011

0.62

0.45

2.1

1.49

1.8

3.8

Farzin, Moassesi, 2014

lP

Method

LOQ (ppb)

Table 5 Determination of Cu2+ and Ni2+ ions in real sample (refined canola and sunflower oils) and relative recovery. Fund before spiking (ppb)

Added (ppb)

Found after spiking (ppb)

Sample

Relative recovery % Cu2+ Ni2+

Ni2+

Cu2+

Ni2+

Cu2+

Ni2+

Refined canola oil

5.50 ± 0.17*

6.20 ± 0.26

30 60 100

20 40 140

31.10 ± 0.40 69.60 ± 0.25 90.70 ± 0.34

22.30 ± 0.30 39.50 ± 0.61 147.50 ± 0.28

85.3 106.8 86.2

80.5 83.3 100.9

Refined sunflower oil

5.80 ± 0.13

7.13 ± 0.14

Refined canola oil + Additives**

5.90 ± 0.14

6.38 ± 0.17

30 60 100 30 60 100

20 40 140 20 40 140

34.0 ± 0.32 67.80 ± 0.45 91.80 ± 0.60 32.12 ± 0.40 68.72 ± 0.62 92.32 ± 0.32

22.73 ± 0.32 41.53 ± 0.71 142.53 ± 0.63 22.58 ± 0.52 41.88 ± 0.37 144.75 ± 0.74

94.0 103.3 86.0 87.4 104.7 86.4

78.0 86.0 96.7 81.0 88.8 98.8

Jo

ur

na

lP

re

-p

*means ± SD, n ≥ 5 **Beta-carotene and Antioxidant.

ro of

Cu2+