Determination of o,o′-Dimethyl-p-Nitrophenyl Thiophosphonate in Methyl Parathion by Photometry Hyphenated with Thin Layer Chromatography

Thin layer chromatography (TLC) was used to separate the main component,o,o′-dimethyl-p-nitrophenyl thiophosphonate (DMNPTP),from the dinitro and o-nitro derivatives which are present as impurities in methyl parathion.Silica gel (G254) was used as the adsorbent and a mixture of petroleum ether and ethylacetate (8+2) was used as the spreading solvent.After separation by TLC,the chromatographic band of the sample which contains the DMNPTP,was taken down from the TLC plate with a razor blade.After removing the organic solvent,and evaporation with HClO4-HNO3 to dryness,the residue was taken up with HNO3 and the PO3-4 transformed from DMNPTP,was determined photometrically be the molybdivanado-phosphoric acid method,measuring its absorbance at the absorption maxima of 450 nm.