Usefulness of Gas Chromatography/Negative Ion Chemical Ionization Mass Spectrometry for Detection of an Organophosphate Pesticide in a Victim

A case is described of a 51-year old male found dead outdoors with froth around his mouth. The presence of aromatic smelling stomach contents suggested the presence of a toxic chemical. The blood, urine and stomach contents, after extraction with organic solvents, were subject to analysis by gas chromatography (GC)/mass spectrometry (MS) in the positive electron impact (EI) mode. The mass spectra showed peaks at m/z 320, 274 and 246. Negative chemical ionization (CI)/GC/MS was also carried out. The negative CI mass spectra of the chemical showed a large anion at m/z 157, which strongly suggested a dimethylphosphorodithioate group of an organophosphate. Therefore, we looked for a dimethylphosphorodiothioate commercially obtainable in Japan, which had a molecular weight of 320 or more. We finally identified the chemical in question as phenthoate (PAP). The present report demonstrates that GC/MS using negative CI in combination with positive EI is extremely useful in the identification of unknown compounds and in this case enabled the identification of the organophosphate pesticide (PAP). The high sensitivity of detection of organophosphates by negative CI/GC/MS was also demonstrated.