Monitoring of 6-chloronicotinic acid in human urine by gas chromatography-tandem mass spectrometry as indicator of exposure to the pesticide imidacloprid

A new analytical method for determining 6-chloronicotinic acid (6-CINA) in human urine is proposed. 6-CINA is the main metabolite in warm-blooded animals after exposure to the insecticide imidachloprid. 6-CINA was extracted from human urine using solid phase extraction (SPE) with laboratory-made cartridges of Amberlite XAD-4. A clean-up step and a derivatization process were carried out prior to gas chromatography-tandem mass spectrometric (GC-MS-MS) determination. A study on the influence of pH in the extraction process revealed that it affects the analyte extraction efficiency. A working pH zone was defined between 0.8 and 2.8. Calibration curves were studied in the concentration range of 0.5-100 ng mL(-1) and showed good linearity. Limits of detection and determination of the method were 16 and 56 pg mL(-1) respectively. The mean recovery at 10 and 100 ng mL-1 was between 97.2 and 102.1% and the repeatability was lower than 5.4% in all cases. The analysis of urine samples of five agricultural workers from Almeria (Spain) did not detect the metabolite.