RESUMO
At present, no official criteria exist for drug identification using single quadrupole mass spectrometers although the European Union (EU) criteria for compound identification have been adopted. These criteria are evaluated with respect to the confirmation of cocaine and its metabolites by single quadrupole liquid chromatography/mass spectrometry (LC/MS) and problems are highlighted. Spiked samples, proficiency testing samples, certified reference materials and samples from real cases that had screened positive for cocaine derivatives by immunoassay were subjected to confirmation by LC/MS using single ion monitoring with in-source fragmentation. The EU criteria for compound identification were applied for the confirmation of cocaine, benzoylecgonine and ecgonine methyl ester. The use of the identification point (IP) system in spiked, proficiency testing samples and certified reference materials provided acceptable results in all cases while in some cases real positive samples did not provide acceptable results. Failure to meet the EU criteria was attributed to low fragmentation at the lower concentrations and the ion suppression effect while both factors affected compliance with the IP system. The identification of cocaine and its metabolites was considerably improved by using a combination of ammonium formate and formic acid as the LC mobile phase. It appears that poor in-source fragmentation in single quadrupole LC/MS and ion suppression may constitute a problem with drug identification when implementing the IP system in real samples, resulting in false negative results. Further investigation is needed for the use of such IP systems to be suitable for use in LC/MS methods.