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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