Identification of opiates in urine by capillary column gas chromatography of two different derivatives

A capillary gas chromatographic method is described for the identification and confirmation of morphine, codeine, ethylmorphine and 6-monoacetylmorphine in urine. The method was useful for forensic purposes, as morphine and 6-monoacetylmorphine could be measured together with the legal drugs codeine and ethylmorphine. The legal non-prescription drug pholcodine could be detected together with the metabolites normorphine and norcodeine. After extraction and evaporation the opiates were derivatized with either N,O-bis(trimethylsilyl)trifluoroacetamide or pentafluoropropionic anhydride, and both types of derivative were chromatographed on a non-polar capillary column with a nitrogen-phosphorus selective detector. The use of two chemically different derivatives was found to be necessary for the unequivocal identification of all opiates of interest, which were not all separated as a single derivative. If a mixture of opiates was subjected to the two different derivatization agents, the derivatives were eluted in a different order. This improved considerably the selectivity of opiate analysis in urine. Particularly difficult samples would require mass spectrometric confirmation.