Development of magnetic dispersive solid phase extraction using toner powder as an efficient and economic sorbent in combination with dispersive liquid–liquid microextraction for extraction of some widely used pesticides in fruit juices
Introduction
Pesticides are chemical compounds that their consumption in agriculture is increased day by day in order to protect the agricultural products in counter to molds, fungi, insects, and any other agents that can affect crops quality and yield [1]. Although the use of pesticides has many merits, but overuse of them can constitute a great menace to the environment and human's health. Hence, it is indispensable to develop simple and sensitive analytical methods which are capable of detecting their trace residue concentrations in food and environmental samples. To date, the methods used for the analysis of pesticides are mostly based on the chromatographic techniques such as high–performance liquid chromatography [2], [3] and gas chromatography (GC) [4], [5]. In order to achieve the reliable results performing a sample preparation step before using the chromatographic techniques is essential. A perfect sample preparation method should be able to extract the analytes from sample matrix and transfer them into a suitable phase for injection into instrumental system [6]. Up to now, various sample preparation methods such as liquid–liquid extraction [7], solid phase extraction (SPE) [8], homogeneous liquid–liquid extraction [9], solid phase microextraction [10], single drop microextraction [11], dispersive liquid–liquid microextraction (DLLME) [12] and etc. have been used for isolation and preconcentration of pesticides from different matrices, and bioactive compounds [13] using also deep eutectic solvents and ionic liquids [14]. Among the above–mentioned methods, SPE is one of the mostly used for matrix simplification and enrichment because of its matured technology, facility of the operation, and the good adaptability towards the multiple sample matrices [15], [16]. Nevertheless, SPE has also suffers some problems like obstruction of cartridges, and necessity of pretreatment of sorbents before extraction procedure [17], [18], [19]. In order to overcome these problems, several other methods based on the traditional SPE methodology, such as dispersive solid phase extraction (DSPE) [20], [21] and magnetic dispersive solid phase extraction (MDSPE) [22], [23] have been developed. In these cases, the sorbent is directly dispersed into the sample solution instead of its packing into a cartridge. Dispersing the sorbent into the sample solution can increase the contact interface between the sorbent and the analytes significantly, and it can improve the mass transfer of the analytes and extraction efficiency [24], [25].
DSPE was introduced by Anastassiades et al. in 2003 [26]. In DSPE, an SPE sorbent is mixed with an appropriate organic solvent (disperser solvent) and dispersed into a sample solution containing the target analytes. After extraction, the sorbent containing the retained analytes is settled by centrifugation. Finally, the analytes are desorbed with an appropriate solvent. The sorbents such as primary secondary amine, C18 (octadecylsilane), and graphitized carbon black are mostly used in this method [27], [28], [29]. In spite of the simplicity and low cost of DSPE, this method needs centrifugation that is time–consuming and can increase the extraction time. MDSPE is a new version of DSPE in which a magnetic sorbent is used instead of the conventional non–magnetic sorbents. The main advantage of this sorbent is that, it can be collected and separated from the aqueous phase using an external magnetic field, which eliminates the centrifugation step and makes the sample pretreatment procedure more convenient, time–saving, and economic. In MDSPE, the type of magnetic sorbent plays a critical role for the effective extraction of the analytes. The commonly used materials for MDSPE include silica (Fe3O4@SiO2) [30], surfactants [31], molecular imprinted polymers (Fe3O4@MIPs) [32], and carbon nanotubes (Fe3O4@CNTs) [33]. The main disadvantage of these magnetic sorbents is that, their synthesis and pretreatment processes are very time–consuming, tedious, and may involve toxic reagents. Therefore, searching a new magnetic sorbent that is simple, eco–friendly, cost effective, and has a high selectivity towards the selected analytes is highly desirable.
In this study, for the first time, a magnetic sorbent (toner powder) which is easy–accessible, and does not need any synthesis or pretreatment, was used as an efficient sorbent in the MDSPE combined with DLLME for the extraction and preconcentration of the trace concentrations of some pesticides from fruit juices prior to their determination by gas chromatography–flame ionization detection (GC–FID). MDSPE–DLLME does not only allow the analytes to be preconcentrated, but also the other compounds present in the sample matrix to be removed. However, MDSPE–DLLME is a bit more expensive and time–consuming than alone DLLME. In the first step of this method, small amount of the sorbent is mixed with the disperser and dispersed into the aqueous solution containing the analytes. Then, the sorbent is collected with the help of an external magnetic field. In the second step, for more enrichment of the analytes an appropriate organic solvent is used to elute the analytes from the sorbent for the following DLLME procedure. Simplicity in the operation, low cost, high enrichment factors (EFs), and rapidity due to use the sorbent which does not need any synthesis, pretreatment or conditioning step, are the main advantages of the proposed method.
Section snippets
Chemicals and solutions
Seven pesticides used in this study including diazinon, oxadiazon, fenazaquin, chlorpyrifos, ametryn, penconazole, and diniconazole were purchased from Dr. Ehrenstorfer (Augsburg, Germany). Acetone, acetonitrile (ACN), chloroform, iso–propanol, and methanol were obtained from Merck (Darmstadt, Germany). Sodium chloride, hydrochloric acid (37%), and sodium hydroxide were also supplied from Merck. 1,2–Dibromoethane (1,2–DBE), 1,1,1–trichloroethane (1,1,1–TCE), and 1,1,2–trichloroethane
Results and discussion
The aim of this study is to develop a new sample preparation method based on the combination of MDSPE using toner powder as an efficient and new sorbent, and DLLME followed by GC–FID determination. Several experimental factors influencing the performance of the introduced method, such as type and amount of sorbent, kind and volume of dispersive solvent, ionic strength, pH, and type and volume of elution solvent (in MDSPE step), and type and volume of extraction solvent, ionic strength, and
Conclusion
In the present work, for the first time, toner powder was used as a magnetic sorbent in MDSPE procedure. It was combined with DLLME as a sample preparation method for the isolation and preconcentration of some pesticides in the fruit juices prior to their determination by GC–FID. The experimental results demonstrated that the proposed method has several advantages over the previously established SPE–based techniques such as easy to operate, good repeatability, high EFs, low LODs, the use of
Acknowledgment
The authors thank the Research Council of the University of Tabriz for financial support.
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