Multicenter evaluation of ultrafiltration, dialysis, and thermal coagulation as sample pretreatment methods for the colorimetric determination of paraquat in blood and tissues.

Three methods of sample pretreatment for the rapid colorimetric determination of paraquat were compared: ultrafiltration, dialysis, and thermal coagulation. Spiked autopsy blood and tissue samples were examined in parallel in Groningen and Krakow and some samples were interchanged. All three methods gave recoveries between 87 to 102%; accuracy at the 20-mg/L level was within 10% of the target value and coefficients of variation in the 10 to 60-mg/L range were between 3 to 15%. Determinations in blood and liver in a fatal case of Gramoxone poisoning showed excellent agreement. Because of its reliability, speed, and simplicity, ultrafiltration is the method of choice.