Ion‐to‐neutral ratio of 2,5‐dihydroxybenzoic acid in matrix‐assisted laser desorption/ionization

Abstract

The ion-to-neutral ratios of 25DHB matrix measured in this work are much smaller than some of the values reported in previous work using different methods and/or under different MALDI conditions.

Ion-to-Neutral Ratios and Thermal Proton Transfer in Matrix-Assisted Laser Desorption/Ionization

“…For example, a thermal ionization of electronically excited matrix model [18] and an energy pooling model [3] predicted the ion-to-neutral ratio of the matrix to be 10 . The ion-to-neutral ratios of the matrix predicted from these two models were approximately 10 4 times greater than those derived from numerous experimental measurements [4,9,17,19], The predicted values were only close to the ion-to-neutral ratios of the analyte for certain analytes but not the ion-to-neutral ratios of the matrix.…”

“…In addition, the original ratios obtained in these four studies have ranged from 2.5×10 −4 to 10 −7 (including the measurements taken outside typical MALDI conditions), but in numerous recently published articles [14][15][16], the values have changed to 10 −3 -10 −4 without being specified for the matrix or the analyte and without clear reasons for the change of values. In our previous report [17], we mentioned that using ion-to-neutral ratios without identifying whether they are for analytes or matrices may cause confusion. Consequently, possible errors may occur in the determination of the MALDI mechanism.…”

Comment on: “Energetics and Kinetics of Thermal Ionization Models of MALDI” by Richard Knochenmuss. J. Am. Soc. Mass Spectrom. 25, 1521–1527 (2014)

“…As the molecules and ions desorbed from surface, the gas plume expanded in the vacuum rapidly. The change of gas plume volume, and therefore the change of neutral and ion concentrations, as a function of time, was estimated based on the relative velocity and angular distribution from previous experimental measurements [24]. Total ion loss was calculated in 1 ps increments until the gas plume volume was very large, such that ion concentration was too low to undergo recombination.…”

Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: Mechanistic Studies and Methods for Improving the Structural Identification of Carbohydrates

“…[27][28][29][30][31][32] For analytes with lower proton a nity, such as carbohydrates, the ionization e ciency drops by a few orders of magnitude to 10 −7 -10 −8 . 23,33,34) A better understanding of mechanisms leads to improvements in the ionization e ciency and increases its e ectiveness toward more elds. Over the last three decades, fundamental ionization mechanisms have been systematically studied by manipulating one or more parameters among di erent matrix systems.…”