Mass spectrometry of medicines. Quantitative determination by direct probe inlet system mass chromatography

A fundamental study was performed to establish a method of quantitative analysis using mass chromatography by the direct inlet system. The samples were aspirin, phenacetin and caffeine, which are often used as cold medicines, and barbital, allobarbital, phenobarbital and phenytoin which are difficult to analyse by gas chromatography in their intact states. N-acetylsulfamine and ethyl p-aminobenzoate were used as internal standards. Direct inlet mass chromatography was performed by an on-line system of the Shimadzu LKB-9000 and the GC-MSPAC 300. The ratio of the cumulative ions of certain peaks of sample and the internal standard was studied. It was found that, whether the sample is a pure reagent or a mixture, the ratio of cumulative ions of a peak specific to the sample and of a selected peak of the internal standard is proportional to the sample size, the error being less than +/- 3.5% for aspirin, phenacetin and caffeine, and less than +/- 2.7% for barbital, allobarbital and phenobarbital. The same relationship was observed for the phenobarbital and phenytoin mixed in rat plasma, the error being less than +/- 2.0%. It can be concluded that this method is applicable to the quantiative determination of medicines in urine, body fluids and other biological samples.