Use of Stable Isotopes in Measuring Low Concentrations of Drugs and Drug Metabolites by GC—MS—COM Procedures

Abstract

Abstract Certain drugs in urine, plasma, breast milk, and amniotic fluid have been quantitatively analyzed in the picogram to nanogram range by selective ion detection with two gas chromatograph—mass spectrometer—computer systems: an LKB 9000/PDP 12 operated in the electron impact mode and a Finnigan 1015/PDP 8/I operated in the chemical ionization mode. With the latter system, it is possible to monitor several drugs and drug metabolites and an internal standard in a single temperature-programmed analysis. Internal standards labeled with stable isotopes are preferred for selective ion detection. Diphenylhydantoin-2,4,5-13C has been used to quantify diphenylhydantoin, and pentobarbital-2,4(6) ,5-13C has been used to quantify amobarbital, secobarbital, caffeine, meperidine ("Demerol"), and phenobarbital in 50-200 µl samples of plasma and breast milk.