A nafion-coated solid phase microextraction fiber modified by ionic liquid and chitosan based on sol-gel process for headspace preconcentration and determination of organophosphorus pesticides by gas chromatography-mass spectrometry using chemometrics methodology

From 1950 to 1970, organophosphorus pesticides (OPPs) were widely used to combat against pests in agriculture and industry, and to control diseases [1]. However, OPPs are in the class of persistent organic pollutants [2]. In this study, a novel sol-gel [3] fiber based on ionic liquid (IL) and chitosan was developed for headspace solid phase microextraction [4] of OPPs from fruit juice samples in ultra-trace levels. The analytes (diazinon, fenitrothion, malathion, ethion and chlorpyrifos) were subsequently analyzed with gas chromatography coupled to selected ion monitoring-mass spectrometer (GC-SIM-MS). Three different coating fibers were prepared including: (a) nafion protected stainless steel wire [5] modified by a sol-gel process, (b) coating prepared from acidic sol-gel in the presence of IL as mediated phase on the surface of nafion peotected stainless steel wire and (c) coating prepared from nafion adhesive, acidic sol-gel, IL and chitosan microspheres on stainless steel wire. All the fibers were conditioned at a temperature of 200 °C. The experiments demonstrated that these fibers have high thermal and chemical stabilities due to the chemical bonding of the nafion with the gel-coating. The scanning electron micrographs of the fibers surfaces revealed that addition of IL and chitosan into the sol solution during the sol-gel process increases the coating thickness, affects the form of fiber structure and also leaves high pores on the fiber surface that cause high surface area and therefore increases sample capacity of the fibers. The important parameters affecting extraction efficiency have been investigated and optimized for the proposed method using Taguchi experimental design. Under the optimal conditions, good linearities were observed for all target pesticides in the range of 4.0 ng L-1-0.3 mg L-1 with the correlation coefficients ranging from 0.982 to 0.998. The detection limits for each OPP were from 0.1 to 2.0 ng L−1 with the relative standard deviations ranging from 3.67% to 4.03% for one fiber (repeatability, n = 5) and from 3.18% to 4.23% for batch to batch fibers (reproducibility, between three fibers, n = 3) respectively.