SECONDARY-ELECTRON RESOLVED MASS-SPECTROMETRY OF ELECTROSPRAYED IONS

An important process in mass spectrometric techniques is the registration of analyte ions at appropriate detector surfaces. Although the nature of the ion-surface interaction can introduce bias in the detection process, such biases can also be exploited to yield complementary information about the detected ions. In this paper, results are presented on the secondary electron yield from impacts of electrosprayed macro-molecular ions on an Al2O3 surface. The secondary electron yield is parametrized as a function of ion mass and velocity. This information is used to acquire mass information (in contrast to the mass-to-charge ratio information gained in quadrupoles and magnetic sector instruments) from the secondary electron yield measured in the detection part of a mass spectrometer. The primary ions are filtered in a scanning mass-to-charge-ratio filter at the same time as mass information from the secondary electron yield is collected. With this method, peaks caused by certain molecules present at low concentrations can be enhanced, and discrimination against low mass ''noise'' can be achieved. Also, peaks with the same mass-to-charge ratio but distinctly different masses can be separately identified. Several practical applications are demonstrated, and evidence for gas-phase fragmentation of large poly(ethylene glycols) is presented.