Development of surface ionization organic mass spectrometer (SIOMS) for the application to forensic toxicology.

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Recently, the issue of drug abuse has become more important in Japan ; more youngsters use abused drugs. Therefore, it is important to establish sensitive determination methods for abused drugs in human body fluids. Surface ionization (SI) is a phenomenon in which tertiary amino compounds convert positive ions on an incandescent surface ; surface ionization organic mass spectrometry (SIOMS) is an application of SI as an ionization method. The SIOMS instrument was a quadrupole mass spectrometer (MS) , which was modified to be usable in both electron impact (EI) and SI modes. For an SI ion source, the direct inlet probe was remodeled to a SI assembly using a rhenium filament, and it was inserted to the center of an EI ion source chamber.We first tried to detect PCP in human body fluids by SIOMS ; its detection limits were 0.05 ng/ml (in mass chromatography, MC) and 0.01 ng/ml (in the selected ion monitoring, SIM) , which were 5 - 200 (in the MC) and 25 - 1000 (in the SIM) times higher compared to previous GC/MS methods. Moreover, background noises were much smaller in the SI mode than the EI mode. SIOMS also gave much higher sensitivity in pentazocine, MPTP and its analogues, pethidine and tricycle antidepressants. In the case of pentazocine, the calibration curves were linear in the range of 6.25 - 100 ng/ml and the detection limits were 0.5 ng/ml in whole blood and urine sample ; the sensitivity for pentazocine obtained by SIOMS in the SIM mode was about 60 times higher than those obtained by EI-SIM. Consequently, SIOMS is highly recommendable for the detection of trace amounts of some abused drugs containing tertiary amino groups in human body fluids.In the future, we are planning to analyze the process of fragmentation of a compound by tandem SIOMS.