A solid phase microextraction coating based on ionic liquid sol–gel technique for determination of benzene, toluene, ethylbenzene and o-xylene in water samples using gas chromatography flame ionization detector

Abstract

Ionic liquid mediated sol–gel sorbents for head-space solid phase microextraction (HS-SPME) were developed for the extraction of benzene, toluene, ethylbenzene and o-xylene (BTEX) compounds from water samples in ultra-trace levels. The analytes were subsequently analyzed with gas chromatography coupled to flame ionization detector (GC-FID). Three different coating fibers were prepared including: poly(dimethylsiloxane) (PDMS), coating prepared from poly(dimethylsiloxane) in the presence of ionic liquid as co-solvent and conditioned at a higher temperature than decomposition temperature of ionic liquid (PDMS-IL-HT) and coating prepared from poly(dimethylsiloxane) in the presence of ionic liquid as co-solvent and conditioned at a lower temperature than decomposition temperature of ionic liquid (PDMS-IL-LT). Prepared fibers demonstrate many advantages such as high thermal and chemical stabilities due to the chemical bonding of the coatings with the silanol groups on the fused-silica surface fiber. These fibers have shown long life time up to 180 extractions. The scanning electron micrographs of the fibers surfaces revealed that addition of ionic liquid into the sol solution during the sol–gel process increases the fiber coating thickness, affects the form of fiber structure and also leaves high pores in the fiber surface that cause high surface area and therefore increases sample capacity of the fibers. The important parameters that affect the extraction efficiency are desorption temperature and time, sample volume, extraction temperature, extraction time, stirring speed and salt effect. Therefore these factors were investigated and optimized. Under optimal conditions, the dynamic linear range with PDMS-IL-HT, PDMS and PDMS-IL-LT fibers were 0.3–200,000; 50–200,000 and 170–150,000pgmL−1 and the detection limits (S/N=3) were 0.1–2 and 15–200 and 50–500pgmL−1, and limit of quantifications (S/N=10) were 0.3–8 and 50–700 and 170–1800, respectively. The relative standard deviations (RSD) for one fiber (repeatability) (n=5), were obtained from 3.1 up to 5.4% and between fibers or batch to batch (reproducibility) (n=3) in the range of 3.8–8.5% for three fibers. The developed method was successfully applied to the real water samples while the relative recovery percentages obtained for the spiked water samples at 20pgmL−1 were from 91.2 to 103.3%.