The internal levels of the organophosphate pesticides Chlorpyrifos or Chlorpyrifosmethyl in persons as a result of occupational or environmental exposure to these substances can be determined by means of this method. For this purpose the specific main metabolite of this organophosphate pesticide, 3,5,6-trichloro-2-pyridinol (TCPyr), is assayed in urine by means of GC/MS-SIM. The acidified urine samples, together with 2,6-dibromophenol, which serves as an internal standard, are hydrolysed at 80

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... C and then subjected to steam distillation. This process completely hydrolyses the TCPyr conjugates and simultaneously separates them from the organic matrix. The distillate is purified over an Isolute ® -101 polymer phase (polystyrenedivinylbenzene copolymer), concentrated and dried. After elution the TCPyr and the internal standard are derivatised with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA). The resulting tert-butyldimethylsilyl ethers are separated by capillary gas chromatography and detected by means of mass spectrometry. Calibration is performed using calibration standards that are prepared in pooled urine and are treated in the same manner as the samples to be analysed. 3,5,6-Trichloro-2-pyridinol (TCPyr) Within-series imprecision: Standard deviation (rel.) s w = 4.2% Prognostic range u = 9.9% at a spiked concentration of 2.5 lg per litre urine and where n = 8 determinations Between-day imprecision: Standard deviation (rel.) s w = 2.0% Prognostic range u = 4.7% at a spiked concentration of 2.5 lg per litre urine and where n = 7 determinations 253 3,5,6-Trichloro-2-pyridinol (TCPyr) 3,5,6-Trichloro-2-pyridinol (TCPyr) Application Determination in urine Analytical principle Capillary gas chromatography/ mass spectrometric detection (MS) Accuracy: Recovery rate r = 104% Test for matrix effects using urine samples from individual test persons (creatinine 0.79 to 4.7 g/L): Standard deviation (rel.) s w = 7.1% Prognostic range u = 16.7% at a spiked concentration of 1.8 lg per litre urine and where n = 5 individual urine samples Accuracy: Recovery rate r = 94% (85 to 103%) Detection limit: 0.05 lg 3,5,6-trichloro-2-pyridinol per litre urine 3,5,6-Trichloro-2-pyridinol (TCPyr) 3,5,6-Trichloro-2-pyridinol (CAS No. 6515-38-4, synonyms: hydroxy-3,5,6-trichloropyridine; 3,5,6-trichloropyridinone) is a white crystalline substance (vapour pressure: 0.00103 mmHg (25 8C), solubility in water: 80.9 mg/L (25 8C)). It is formed during the intermediate metabolism of the organophosphate pesticides Chlorpyrifos and Chlorpyrifos-methyl (see Figure 1 ). 3,5,6-Trichloro-2-pyridinol (TCPyr) 3,5,6-Trichloro-2-pyridinol (TCPyr) Application Determination in urine Analytical principle Capillary gas chromatography/ mass spectrometric detection (MS)