Phosphine detection in veterinary samples by headspace GC/MS/MS with Multiple Reaction Monitoring

RATIONALE: Determination of phosphine exposure from zinc or aluminum phosphide fumigants continues to be a routine analytical requirement in veterinary forensic toxicology. There is a need for a more reliable and specific method than simple GC/MS analysis of sample solvent extracts, as GC/MS of extracts on capillary columns used for general screens invoke significant interference from air peaks. METHODS: GC/MS/MS headspace analysis of acid-generated phosphine gas enabled study of the feasibility of devising Multiple Reaction Monitoring approaches to phosphine with greater specificity. RESULTS: Collision-induced dissociation in GC/MS/MS showed that phosphine generated m/z 3431, 32 and 33 ion transitions by sequential proton release as well as minor transitions m/z 3447, 63 and 6331.5 by intermolecular collisions and doubly-charging. Study of the formation of these product ions enabled development of MRM settings for a highly useful headspace method for phosphine detection. CONCLUSIONS: The method was validated over a working range of 5-100 ppm of phosphide generating phosphine gas which enabled retention of regular screen capillary columns without necessitating separation from air components. The method should have adequate sensitivity and reliability for veterinary toxicology labs confronting specimens from animals poisoned by crop fumigants.