Laser desorption in a quadrupole ion trap: mixture analysis using positive and negative ions

We demonstrate the generation of both negative and positive ions by laser desorption directly within a quadrupole ion trap and the application of this method to analyze complex samples containing compounds such as explosive residues, metal complexes, and polynuclear aromatic hydrocarbons. In some cases the ability to rapidly switch between positive and negative ion modes provides sufficient specificity to distinguish different compounds of a mixture with a single stage of mass spectrometry. In other experiments, we combine intensity variation studies with tandem mass spectrometry experiments and positive and negative ion detection to further enhance specificity. 55 refs., 8 figs., 1 tab.