Comparison study of the extraction methods of paraquat in post-mortem human blood samples

The most important step for Paraquat analysis in post-mortem human blood (PMB) is its extraction from the specimens, as Paraquat is insoluble in organic solvents due to its ionic form. The most common extraction method, solid phase extraction (SPE), has been used for the extraction of Paraquat from PMB. However, SPE procedures are somewhat time-consuming, and resulted in unsatisfactory recovery in our laboratory. Therefore, SPE procedures, with five extraction solvents for the liquid-liquid extraction (LLE) of paraquat in PMB, were compared using HPLC, and the chloroform-ethanol (7:3, v/v) solvent mixture was found to be the most effective. The recoveries of Paraquat using the 7:3 solvent mixture in human whole blood samples, which were already spiked with paraquat standards (1.05, 2.10 and 4.21 microg/mL) averaged 98.20, 105.71 and 99.40%, but the recoveries from the SPE were about 74.29, 78.50 and 80.10%, respectively. Linearity was obtained for the range of Paraquat standards, with a correlation coefficient; r2 > 0.999. The limit of detection (LOD, with S/N > or =3) and limit of quantitation (LOQ, with S/N > or =10) were 0.01 and 0.05 microg/mL, respectively. The extraction method was successfully applied to seven real post-mortem cases involving paraquat poisoning.