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™/divinylbenzene (CW/DVB 65 μm) and polydimethylsiloxane (PDMS 100 μm). 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 μL 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 μg/mL for blood, and 0.01 to 50 μg/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.