Detecting MALDI ions with a cryogenic detector
Progress in cryogenic detector technology has led to the development of new devices appropriate for use as ion detectors. We have recently begun to evaluate one type of cryogenic detector called a superconducting tunnel junction (STJ) detector. Initial tests were conducted by replacing a microchannel plate ion detector in a matrix-assisted-laser-desorption time-of-flight mass spectrometer (MALDI-TOF-MS) with a STJ detector. In those initial tests we showed that 1) the STJ detector produces pulses appropriate for timing large ions and 2) the height of the pulses is proportional to ion energy and thus useful for deducing ion charge. We now report additional STJ ion energy measurements that help to reveal some aspects of ion fragmentation in MALDI mass spectrometry. The height of the output pulse from a STJ detector is related approximately linearly to ion energy, thus doubly charged ions in a MALDI:TOF-MS produce pulses about twice as large as singly charged ions. Cryogenic detectors show excellent energy resolution for X rays, but poorer energy resolution is observed when MALDI ions are analyzed. The cause for the poor energy resolution of MALDI ions is not fully understood; nevertheless, it appears feasible to use STJ detectors to study the energy distribution of MALDI ions. The detectors appear to be sensitive enough to measure individual ion impacts and processes which influence ion energy such as in-source fragmentation and the deficit of ion energy caused by accelerating ions through a MALDI plume. In this study, we show how a STJ detector can be used to measure the time of flight of macroglobulin ions (725,000 Daltons), determine ion charge using detector pulse height and investigate in-source fragmentation patterns. It is found that the energy response of the STJ detector not only provides a way to assign charge to ions but also provides a way to examine fragmentation patterns for MALDI ions. The simple model described above appears to account for the flight times and expected energy of the ions that lead to clusters of crescent shaped data points. Work is under way to investigate the fragmentation of multiply charged ions.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6374
- Report Number(s):
- LBNL-40059; ON: DE00006374
- Resource Relation:
- Conference: 14th IMSC International Mass Spectrometry Conference, Tampere, Finland, August 25-29, 1997
- Country of Publication:
- United States
- Language:
- English
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