Normal- and reversed-phase thin-layer chromatography of three structurally related organophosphorus pesticides of forensic importance

Abstract

Recently, considerable numbers of poisoning cases have been reported owing to the ingestion of three structurally related or-ganophosphorus pesticides (OPPs): chlorpyrifos (C), quinal-phos (Q), and triazophos (T). Normal-phase high-performance thin-layer chromatography (NP-HPTLC) on silica gel 60 F254 and reversed-phase (RP)-HPTLC on silica gel 60 RP-18 W F254 were used to evaluate the retention and separation data for these three pesticides. Optimum separation of pesticides has been achieved on NP-TLC layer with n-hexane?acetone 9:1 (v/v) and on RP-TLC layer using acetonitrile?water 8:2 (v/v) as the mobile phases. The RF values of pesticides increased with increasing acetone content in the case of NP-HPTLC and decreasing water content in RP-HPTLC. Under the chromatographic conditions used, in regard to changes in the mobile phase composition, C adsorbed most strongly on the silica gel RP-18 plate. A linear relationship between RM values and mobile phase composition was established. Densitometric detection was performed at the respective ?max value of the pesticide. The peak resolution (RS) was greater than 1.25 for all compound pairs (C-Q, Q-T, and C-T). The pesticide samples are stable on plate and in solution at room temperature as well as at 4°C. The ultraviolet (UV) spectra (?max) of the OPPs were apparently unaffected by changes in pH. No significant chromatographic interference was noticed from other OPPs of forensic relevance. © Akadémiai Kiadó, Budapest.