title: Properties of matrix-assisted laser desorption. Measurements with a time-to-digital converter.
abstract: 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.
authors.affiliation: Department of Physics, University of Manitoba, Winnipeg, Canada.
authors.forename: W
authors.initials: W
authors.lastname: Ens
authors.forename: Y
authors.initials: Y
authors.lastname: Mao
authors.forename: F
authors.initials: F
authors.lastname: Mayer
authors.forename: K G
authors.initials: KG
authors.lastname: Standing
mesh_terms: D000818:Animals; D002417:Cattle; D007328:Insulin / Q000032:analysis; D007834:Lasers; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*
chemical_list: D007328:Insulin