Programmable selected ion monitoring for quantitative analysis of biological samples with a GC-MS-computer system

Maximum sensitivity of a mass spectrometer used as a detector for a gas chromatograph can be achieved by monitoring only the ion current at a single mass per charge. However, greater confidence in the analytical results can be achieved by monitoring at least 2 ions from a compound of interest. Since a biological sample may contain several different compounds of interest, it may be desirable to monitor as many as 8 to 12 different ions so that all components may be quantified. However, the greater the number of ions monitored, the poorer the signal to noise ratio available for monitoring any given ion current. A compromise between obtaining maximum sensitivity and confidence in analytical results can be achieved by monitoring only 2 or 3 ions during any given time interval of the gas chromatogram when the corresponding compounds are expected to emerge from the GC. This procedure is illustrated with a computer (PDP-12A)-controlled dodecapole gas chromatograph-mass spectrometer with analyses of prostaglandins and biogenic amines