Evaluation of a benchtop capillary gas chromatograph-mass spectrometer for clinical toxicology

We evaluated the Hewlett-Packard 5995B benchtop capillary gas chromatograph-mass spectrometer (GC-MS) for its ability to identify drugs commonly detected and (or) measured in the clinical toxicology laboratory. Initial experiments indicated that the instrument as originally configured, with an isolation valve between the gas chromatograph and mass spectrometer, was unsatisfactory for the identification of hypnotics-sedatives. However, with the capillary inserted directly into the ion source, we could detect 10 ng of these drugs on a total-ion chromatogram. The software programs cause the instrument to be highly automated. In terms of ease of operation and speed it was found suitable for use in a routine clinical laboratory. Chromatography of urine extracts on the capillary gas chromatograph-mass spectrometer yielded excellent resolution of parent compounds and metabolites (e.g., diphenhydramine together with approximately four metabolites and propoxyphene with four metabolites). However, the manufacturer's computer program used to evaluate the quality of the match between the experimental mass spectra and the 375 drug reference spectra was only moderately successful in identifying unknown compounds. The ability of this capillary GC-MS to identify most compounds with a high degree of confidence will be increased by enlarging the library to include more drugs and metabolites and by using a more reliable computerized matching program.