A novel analytical screening procedure has been developed, using computer-controlled gas chromatography-mass spectrometry (GC-MS), to detect 120 drugs of interest to road safety. This paper describes GC-MS methodology suitable for use on extracts of biological origin, while extraction procedures will be the subject of a future communication. The method was devised to identify drugs in extracts of blood samples, as part of an investigation into the involvement of drugs, other than alcohol, in road accidents. The method could be adapted to screen for other substances. The method depends on a "macro" program which was written to automate the search of GC-MS data for target drugs. The strategy used was to initially search for each drug in the database by monitoring for a single characteristic ion at the expected retention time. If a peak is found in this first mass chromatogram, a peak for a second characteristic ion is sought within 0.02 min of the first and, if found, the ratio of peak areas calculated. Probable drug identification is based on the simultaneous appearance of peaks for both characteristic ions at the expected retention time and in the correct ratio. If the ratio is outside acceptable limits, a suspected drug (requiring further investigation) is reported. The search macro can use either full mass spectra or, for enhanced sensitivity, data from selected ion monitoring (which requires switching between groups of ions during data acquisition). Quantitative data can be obtained in the usual way by the addition of internal standards.
Drug Evaluation, Preclinical Electronic Data Processing