Detection of O,O,S-trimethyl phosphorodithioate, an impurity in phenthoate(PAP), in komatsuna

An unknown peak (peak A) was detected in a mass chromatogram of komatsuna e xtract containing a high concentration of phenthoate (PAP), and it was cons idered to be O,O,S-trimethyl phosphorodithioate (OOS). Although it is gener ally known that OOS exists as an impurity in technical malathion and PAP, i t has not been reported that OOS is present in crops. Since an OOS standard is not commercially available, OOS was separated and purified from commerc ial emulsifiable malathion. Peak A was confirmed to be OOS by GC/MS using t he purified OOS. The concentration of OOS was estimated to be 0.02 mug/g. I t is supposed that OOS was detected in crops because they contained a high concentration of PAP residue.