simultaneously cooling assisted headspace and fiber in headspace solid-phase microextraction coupled to gc-ms for the determination of pesticides in soil

For volatiles, trapping and adsorption of analytes on solid phases is very important [1]. also for semi-volatile analytes, low volatility is a challenge. to overcome these limitations, thermal desorption and use of an organic solvent to release analytes from their matrix often are suggested [1,2]. thermal desorption is a simple and most effective approach that can enhance the mass transfer process and increase the vapor pressure of the analyte. headspace solid-phase microextraction (hs-spme) combined thermal desorption is a conventional method that is used for the analysis of volatile and semi volatile analytes [3]. however, applying high temperatures in this method can decrease the extraction from headspace because of reducing the partition coefficients of the analytes. this problem can be overcome by simultaneously heating the sample matrix and cooling the extraction phase. acceleration of mass transfer and increasing the temperature gap between the sample and sorbent are achieved by this strategy [1]. the use of a cooling assisted (ca) method for spme was first reported by pawliszyn et al. [4]. in this paper, in addition to cooling the fiber, the head space containing the analyte around the adsorbent was cooled. this increases the concentration of analyte around the fiber. as a result, the efficiency of the method increases. the proposed method is evaluated for the extraction of pesticides such as fenvalerate and chlorpyrifos. optimization of the extraction parameters was carried out using a gc–ms instrument. to optimize the extraction parameters such as the moisture and temperature of the sample and fiber, and time of the extraction a simplex method was used as an easy and fast optimization technique. under the optimized conditions, linear calibration curves were obtained for the analytes within a range of 1.2 ng g-1 up to 9000 ng g-1, with determination coefficients that ranged from 0.989 to 0.991. the limits of detections were between 0.89 to 1 ng g-1 and the coefficients of variation for 5 replicates were between 2.6 to 4.1%. the method was successfully applied to the gc-ms analysis of pesticides in soil samples.