期刊
INTERNATIONAL JOURNAL OF MASS SPECTROMETRY
卷 221, 期 1, 页码 67-81出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/S1387-3806(02)00898-9
关键词
MALDI; threshold; laser fluence; ion yield
Ion yields in matrix-assisted laser desorption ionization have been measured as a function of laser fluence using pulse-counting and analog detection methods in the same TOF instrument configured in the usual axial geometry. In addition, measurements have been made using pulse-counting methods in an orthogonal-injection TOF instrument, which uses collisional cooling to spread the plume along the injection axis. This allows pulse-counting methods to be used without ambiguity as to the number of ions striking the detector, and extends the dynamic range over which pulse-counting can be used reliably without changing the instrument transmission. All measurements indicate a steep power-law dependence of the ion yield on fluence with an exponent in the range of 7-9. The same power-law dependence extends below the fluence usually associated with a threshold in analog measurements by at least a factor of two, and the data show no indication of physical fluence threshold. (C) 2002 Elsevier Science B.V. All rights reserved.
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