A novel mass spectrometer with an external ionization source can be used to detect picogram quantities of compounds of biologic interest. The source contains a 63Ni foil, and is at atmospheric pressure. Samples are introduced in a flowing gas stream in selected common solvents. Positive ions are formed by a complex series of ion molecule reactions. The ionization reaction for the sample may involve either proton transfer or charge transfer. Negative ions are formed by either resonance or dissociative capture of thermal electrons, or by ion-molecule interactions. In a favorable case (very little adsorption on the reaction chamber walls), 5-10 picograms could be detected by single ion monitoring, and a scanned mass spectrum could be obtained with as little as 25 picograms. The potential uses include incorporation into LC-MS-COM and GC-MS-COM analytical systems.

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Finally, the validity of employing "half-intensity" integrations is tested. When full resolution of a profile is lacking but the central portion of the profile is not affected by interferences which occur on only one side of the profile, then the profile is scanned from its free side and the intensity integration is performed only for the free half of the profile, that is, up to the peak-height channel. A user option programs profiles for half-intensity integration at the time of acquisition. The results in Table V indicate excellent precision for 9Be, an isotope for which all lines were computed by half-intensity integration. Also, the effect of mixing half-intensity and full-intensity calculations has not harmed the precision for integrated intensity vs. peak-height intensity for those isotopes so indicated in Table V.