Ionic liquids extraction of Para Red and Sudan dyes from chilli powder, chilli oil and food additive combined with high performance liquid chromatography
Introduction
Sudan dyes (I, II, III and IV) are typically used as coloring additives in the manufacturing of some products, such as wax, textile, and floor and shoe polishes [1], [2]. Sudan I has been classified as a category 3 carcinogen by the International Agency for Research on Cancer (IARC). Sudan II is the dimethyl derivative of Sudan I. Both Sudan I and Sudan II have been proven to be carcinogens to humans by many research [2], [3]. Para Red is very chemically similar to Sudan I. Although data available are few, scientists have advised that Para Red could be a genotoxic carcinogen [4]. Therefore, the use of these dyes in food stuff is prohibited world widely. Nevertheless, for many years Sudan dyes have been used as additives in food products by some factories because of their intensive red–orange color, which is a great risk to human health.
Recently, high performance liquid chromatography (HPLC) coupled with different types of detectors including mass spectrometric detector (MSD) [5], [6], [7], [8], ultraviolet-visible detector (UVD) [4], [9], [10] and photodiode array detector (DAD) [11] were widely employed for the determination of Sudan dyes in foodstuffs. Whichever method is used, sample pretreatment procedure is a prerequisite. Solvent extraction [4], [6], [7], [8], [10], [11], [12], [13] and the imprinted functionalized silica gel sorbent based on-line solid phase extraction (SPE) [9] techniques have been employed for this purpose. In solvent extraction methods, the matrix was mixed with volatile organic solvent at a certain proportion for a period. After centrifugation, the extract was transferred for detection or evaporated to dryness and the residue was dissolved in a small amount of conventional organic solvent and used for analysis. The imprinted functionalized silica gel sorbent based on-line SPE also involved the use of acetonitrile for extraction of Sudan I in chilli powder before on-line preconcentration. Unfortunately, such organic solvents used in those processes like acetone, methanol, and dichloromethane, are volatile, flammable and toxic.
Ionic liquids (ILs), sometimes called molten salts, are liquids entirely composed of organic cations and inorganic or organic anions at or close to the room temperature. ILs are regarded as potentially environmentally benign solvents because they have no-detectable vapor pressure. They also have the characteristics of high thermal stability, non-flammability and good solubility for inorganic and organic compounds. Furthermore, their chemical and physical properties (melting point, density, water immiscibility, viscosity, etc.) can be easily modified by suitable combination of different cations and anions [14]. Therefore, ILs have been extensively investigated as replacements for conventional organic solvents in extraction processes including liquid–liquid extraction (LLE) [15], [16], liquid phase microextraction (LPME) [17], [18], solid phase microextraction (SPME) [19], [20], liquid–solid extraction (LSE) [21], [22], [23], [24], and other applications (catalytic [25], synthetic [26] and electrochemical applications [27], etc.). Several excellent reviews have compiled the applications of ILs in analytical chemistry [28], [29], [30], [31], [32], [33]. Although presently the cost of ILs compared to conventional organic solvents is much higher, recent advances in the production of a wide variety of ILs would have drastically reduced it [34], [35].
The main purpose of the present work was to evaluate the possibility of using an IL to extract Sudan dyes (I, II, III and IV) and Para Red from chilli powder, chilli oil and food additive samples. Two ILs, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]), were compared as extraction solvents. Different experimental parameters affecting the extraction efficiency were optimized for the HPLC assay procedure using a variable wavelength detector (VWD). Because of the nonvolatility of the ionic liquids, the proposed method was environmentally friendly with good repeatability and spiked recoveries.
Section snippets
Reagents and materials
Sudan dyes (I, II, III and IV) and Para Red standard solutions (200 mg L−1) were obtained from Zhejiang Entry-Exit Inspection and Quarantine Bureau (Hangzhou, China) and stored in refrigerator at 4 °C. HPLC-grade methanol was purchased from Hengtian Industrial & Trade Co., Ltd. (Huaian, China). 1-Chlorobutane (99.5%) and 1-chlorooctane (99%) were purchased from Sanyou Chem. Co. (Jiangsu, China), 1-methylimidazole (99%) was obtained from Kaile Chem. Co. (Zhejiang, China), and Milli-Q (Millipore,
Results and discussion
In the present work, experimental parameters affecting IL extraction such as the alkyl chain length on the imidazolium ring of IL, the volume of IL and the extraction time, were optimized for chilli powder samples spiked with 4.0 mg kg−1 of Para Red, Sudan II and Sudan III and 6.0 mg kg−1 of Sudan I and Sudan IV and for chilli oil samples (as representative samples of oil matrices) spiked with 2.0 mg L−1 of each analyte. The stirring rate of magnetic stirrer was set at 600 rpm during the extraction of
Conclusions
In the present work, an environmentally benign extraction method using ionic liquids in place of conventional organic solvents has been successfully applied for the HPLC determination of Para Red and Sudan dyes in chilli powder, chilli oil and food additive samples. Compared with conventional method, small sample and IL volume are required for successful and efficient sample extraction with satisfactory and comparable recoveries being achieved. Moreover, the complicated and tedious steps of
Acknowledgements
This research was financially supported by the National Natural Science Foundation of China (No. 20775070), Zhejiang Provincial Natural Science Foundation of China (Nos. R4080124, Y507252) and Zhejiang Qianjiang Project of Science and Technology for Competent People (2008R10028).
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