Determination of quinalphos in blood and urine by direct solid-phase microextraction combined with gas chromatography-mass spectrometry

A new method based on direct solid-phase microextraction (DI-SPME) followed by gas chromatography-mass spectrometry was developed for the purpose of determining quinalphos in blood and urine. Two types of coated fibre have been assayed and compared: carbowax (TM)/divinylbenzene (CW/DVB 65 mu m) and polydimethylsiloxane (PDMS 100 mu m). The main parameters affecting the SPME process such as temperature, salt addition, pH, stirring and adsorption/desorption time profiles were optimized to enhance the sensitivity of the procedure. The method was developed using only 100 mu L of blood and urine. Limits of detection of the method for blood and urine matrices were, respectively, 10 and 2 ng/mL. Linearity was established over concentration ranges from 0.05 to 50 mu g/mL for blood, and 0.01 to 50 mu g/mL for urine, with regression coefficients ranging between 0.9991 and 0.9999. Intra- and interday precision values were less than 13%, and accuracy was within 15% of the nominal concentration for all studied levels in both matrices. Absolute recoveries were 14 and 26% for blood and urine, respectively. (c) 2005 Elsevier B.V. All rights reserved.