Properties of matrix-assisted laser desorption. Measurements with a time-to-digital converter.
Some properties of matrix-assisted laser desorption have been studied using single-ion-counting methods and a time-to-digital converter. The methods allow examination of the process for irradiances near the reported threshold for observation with a transient recorder. All measurements were made using bovine insulin as a test compound. We present direct evidence that an irradiance threshold near 10(6) W cm-2 exists for ion production, and that the process is a collective effect, either involving a large number of molecular ions (approximately 10(4) in a successful event or none at all. Above the threshold, the yield is found to scale with a high power (4th to 6th) of the irradiance. Measurements of initial velocity distributions indicate an axial velocity spread corresponding to approximately 50 eV and a radial velocity spread corresponding to approximately 2.4 eV. Thus the ejection or extraction mechanism appears to be strongly asymmetric.
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Department of Physics, University of Manitoba, Winnipeg, Canada.
Mao
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Mayer
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Standing
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D000818:Animals; D002417:Cattle; D007328:Insulin / Q000032:analysis; D007834:Lasers; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*
D007328:Insulin