Acid Spray for Enhancement of MH+ Ion Intensity in Secondary Ion Mass Spectrometry

The addition of acid into a sample solution often enhances the protonated molecule (MH+) sensitivity in secondary ion mass spectrometry and fast atom bombardment mass spectrometry. In the present study, acid was supplied as an acid vapor sprayed over a sample surface from the tip of a capillary. The spray was easy to control from outside of the ion chamber in the course of the experiment. Intense ion signals of MH+ were found to last longer with this spraying method, which caused more improvement in sensitivity than in the case of conventional mixing method. The degree of sensitivity enhancement was found to be virtually independent of the concentration of the acid.