Determination of paraquat from formalin-fixed tissue

In this paper, a sulfuric acid digestion method and a clean-up technique by using cation exchange resin followed by XAD-2 resin has been developed for the determination of paraquat from formalin-fixed tissue at the submicrograms per gram level. Formalin-fixed tissue is dissolved by hot sulfuric acid, then paraquat is isolated and purified with cation exchange chromatography. The eluted paraquat forms an ion-pair with sodium dodecyl sulfate, it is then adsorbed on XAD-2 resin. Paraquat is eluted, extracted and reduced with solvent mixtures, NaCl solution and dithionite reagent, respectively. The calibration graphs of zero-order and second-derivative spectroscopy are linear in the range of 0.01-5.0 mg/kg. The relative standard deviation was less than 5% and the detection limit was 0.02 mg/kg based on 0.5-g samples. The sensitivity of the proposed method could be increased by using larger sample sizes. The method was precise and gave a quantitative recovery of paraquat spiked into formalin-fixed liver homogenates (78%). The proposed method has been satisfactorily applied to the determination of paraquat in the formalin-fixed tissues of suspected poisoned cases. It has been shown to be of great value in the field of forensic toxicology especially when formalin-fixed tissue only is available.