Elsevier

Journal of Molecular Liquids

Volume 279, 1 April 2019, Pages 571-577
Journal of Molecular Liquids

Application of deep eutectic solvent in ultrasound-assisted emulsification microextraction of quercetin from some fruits and vegetables

https://doi.org/10.1016/j.molliq.2019.01.130Get rights and content

Highlights

  • A novel green deep eutectic solvent-based ultrasound-assisted emulsification procedure was developed for quercetin.

  • The influences of matrix components were investigated.

  • The method has been applied to the determination of quercetin in fruit and vegetable samples.

Abstract

A deep eutectic solvent ultrasound-assisted emulsification microextraction (USAEME-DES) procedure for the separation and preconcentration of quercetin in vegetable and fruit samples has been established. An alcohol-based extraction has been applied as sample pre-treatment step prior to microextraction procedure. Quercetin was extracted into DES phase (tetrabutylammonium chloride: decanoic acid (TBACl-DA, 1:3 M ratio) and analyzed by UV–VIS spectrophotometry at 370 nm. For the quantitative recoveries of quercetin, optimal pH, sample solution volume, volume and kind of DES, and ultrasonication time were 3.0, 15 mL, 250 μL of 1:3 M ratio of TBACl-DA acid and 5 min, respectively. The influences of matrix constituents were also studied. The developed method has a limit of detection (LOD) of 18.8 μg L− 1 and a relative standard deviation (RSD) of 5.1%. The developed procedure was applied to analysis of vegetable and fruit samples, which prepared by alcohol based extraction step.

Introduction

Quercetin, (2-(3,4-dixydroxyphenyl)- 3,5,7-trixydroxy-4H-1-benzopyran-4-one), is a flavonoid widely available in many vegetables and fruits like tea, onions and apples or their byproducts like red wine [1,2]. Moreover, due to its being the important dietary component, several pharmaceutical products that contain quercetin with vitamin C or other flavonoids are produced and available at pharmacy stores.

Various analytical techniques such as capillary electrophoresis (CE), UV–VIS spectrophotometry, gas chromatography (GC), high-performance liquid chromatography (HPLC) and fluorescence spectrophotometry have been used for the determination of quercetin in different samples [[3], [4], [5], [6], [7], [8]]. Among of them, Although the use of UV–VIS spectrophotometry offers considerable advantages [7,8], direct analysis of quercetin without separation/enrichment method by using UV–VIS spectrophotometry is difficult because of the complex real sample matrix, low concentrations of quercetin in sample matrix and similar chemical structure with other flavonoids which given similar absorption peak in close region to quercetin. In order to eliminate these problems, different types of traditional separation/preconcentration methods such as liquid–liquid extraction (LLE), solid phase extraction (SPE) and cloud point extraction (CPE) have been developed [[9], [10], [11], [12], [13], [14]]. As a matter of fact, these methods lead to some drawbacks e.g., like use of high volume of toxic solvents, generation of secondary wastes, time consuming experimental stages. Hence there is still a great need for methods that fulfill the requirements of green analytical chemistry.

In extraction studies, liquid phase microextraction (LPME) and solid phase microextraction (SPME) methods for the trace species have been employed as new generation separation/preconcentration procedures in recent years [[15], [16], [17], [18], [19], [20], [21]]. However, these microextraction methods are judged to be the green methods according to the solvents used. These criteria are as follows; usage of safety, environmentally friendly and healthy solvents instead of hazardous solvents; adaptation of “bio-solvents” obtained from renewable resources to sample preparation methods; substitution of toxic organic solvents with environmentally friendly ionic liquids (ILs) with a low vapor pressure.

Ionic liquids are often used in microextraction methods as “green solvents” due to their special chemical and physical features. On the other hand, though some scientists reported the green features of ILs [22,23], some reports have highlighted the toxic effect and very poor biodegradability of most ILs [24,25]. Moreover, further development and applications of ILs have been limited because of their high cost and the necessity of pure forms.

In order to solve the toxicity and high cost problems of ILs, scientists have focused on the finding new green solvents. Deep eutectic solvents (DESs) have started to grab more attention as new green- ionic solvents in recent years. They are advantageous due to the accessibility of materials, low toxicity and ease of synthesis [26,27]. DESs have been widely used in many analytical applications. Some of example applications are following as; Khezeli et al. used DESs for microextraction of caffeic, cinnamic and ferulic acid in almond, olive, cinnamon and sesame oil samples prior to HPLC-UV determination [28]. Dai et al. used natural DESs for extraction of phenolic metabolites in Carthamus tinctorius L [29]. In a different microextraction application, DESs were applied to preconcentration of lead and cadmium in edible oils prior to ETAAS determination [30]. In a different analytical application, DESs were used as a sol-gel sorbent coating material to obtain of DES modified poly(dimethylsiloxane) (PDMS) fiber [31]. The obtained material was used for solid phase microextraction of toluene, ethylbenzene and o-xylene in water samples prior to GC-FID detections [31]. Shekaari et al. used DESs for effective extraction of benzene and thiophene [32]. Li and Row prepared DES modified molecularly imprinted polymers as sorbent for solid phase microextraction of 3,4-dihydroxybenzoic acid prior to HPLC analysis [33]. Wang et al. has been prepared and used poly(deep eutectic solvent) monolithic minicolumn for in-tube solid phase microextraction of non-steroidal anti-inflammatory drugs (NSAIDs) in aqueous samples [34].

In this study, an ultrasound assisted emulsification microextraction procedure based on deep eutectic solvent has been established for the separation and preconcentration of trace amount of quercetin from vegetable and fruit samples followed by its UV–VIS spectrophotometric determination.

Section snippets

Instrumentation, reagents and solutions

A Hitachi UH 5300 spectrophotometer with quartz micro–cell, WTW model 730 pH meter, a Hettich Universal 320 centrifuge (Tuttlingen, Germany) device and Sonorex, Model No DT-255 ultrasonic sonicator were used for throughout all analysis operations. A Millipore water purification system (Millipore, Bedford, MA, USA) was used for purification of the water (18.2 MΩ cm). Proton Nuclear Magnetic Resonance (1H NMR) spectra for the prepared DESs were recorded at 25 °C on a 400 MHz Bruker 400. All

Characterization of TBACl-DA DES

Characterization studies for prepared TBACl-DA DES were carried out by H-NMR, FT-IR and viscosity measurement analysis. For H-NMR studies, changing in the integral of the groups were examined. The results are given in Fig. 2 and Table 1. The results showed that there were importance differences between expected and measured integrals. It can be explained with the formation of new structure (DES) as a result of changing in distribution of protons in TBACl and DA with mixing of TBACl and DA.

Conclusions

A microextraction method based on DES consisting of tetrabutylammonium chloride/decanoic acid (1:3) was suggested to determine the quercetin in vegetable and fruit samples. Facile synthesis of DESs using available and quite safe reagents as well as cheap and simple apparatus, and analysis of quercetin with cheap and simple available UV–VIS spectrometer is the main beneficial spots of this USAEME-DES-UV–Vis method. The developed USAEME-DES-UV–Vis method has better or comparable limit of

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