MoP-14


THE USE OF BENCHTOP GC/MS/MS IN CLINICAL AND DRUG ANALYSIS

Annabel Mitchell1 and Terry Sheehan2

1Varian Australia, 679 Springvale Road Mulgrave , Vic 3170, Australia
2Varian Chromatography Systems, 2700 Mitchell Drive, Walnut Creek, CA, USA 94598


Because of the sensitivity limitations of full scan detection, many early GC/MS methods for drug analysis were developed using Selected Ion Monitoring (SIM) of three to five ions per compound. Ratios for these ion intensities replaced library searches as the typical approach to spectral confirmation of the analyte's identity. While these SIM methods were absolutely essential to the early acceptance of GC/MS within the trace level constraints of drug analysis, the probability of false positive and negative results has remained too high to avoid results being successfully contested in a court of law. The need clearly exists for more selective detection processes which avoid interferences from the complex sample backgrounds common to biological matrices. This requirement is further increased by the availability of drugs with more potent activity and, in turn, lower levels in biological samples.

Ion trap technology has recently given the drug analysis laboratory a more selective tool with an excellent signal to noise ratio (lower detection limits). GC/MS/MS, which has typically been viewed as an expensive research tool, is now available as an inexpensive, easy to use, benchtop GC/MS option. The three step MS/MS process of ion isolation; collision induced dissociation; and full scan of product ions is clearly more selective than either full scan or SIM modes of MS operation. Adjustment of the energy of collision induced dissociation (CID) accounts for part of that selectivity enhancement. Equally important, however, is the unique relationship between parent (precursor) and daughter (product) ions. Even in cases of coelutions which generate interferences with the ions chosen for SIM or full scan quantitation, MS/MS can generate daughter ions free of any interference. While signal typical decreases in the MS/MS, the multi-step process eliminates almost all of the chemical background which yields a much greater decrease in the noise. MS/MS yields remarkably flat, simple baselines with relatively simple, clean spectra. Low to sub picogram detection limits are common for MS/MS even in the presence of a biological matrix. The advantage of MS/MS will be demonstrated for a wide variety of drugs of abuse (opiates, barbiturate, amphetamines, benzodiazepines),THC, and doping analyses for sports medicine. The use of of isotopically labeled internal standards through MS/MS techniques like Multiple Reaction Monitoring will also be reviewed.