The validation of exact mass measurements for small molecules using FT-ICRMS for improved confidence in the selection of elemental formulas

The confidence in an individual measurement is the most important factor when selecting the elemental formula candidates from the list of possible elemental compositions following an exact mass measurement. It is the single mass measurement capability rather than the averaged mass measurement potential of the mass spectrometer that is the critical factor when validating the exact mass measurements of small molecules. Here, an experimental protocol has been established to determine the frequency of exact mass measurement by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) at known relative ion abundance ratios (RA). This in turn allows for statements about the confidence limit for any single exact mass measurement to be made. This is particularly crucial for a high throughput, automated environment where operator intervention is required to be minimal and repeat analyses are to be avoided. The relative ion abundance calculations are essential to determine the working ranges for specific sample ion abundances. Further, it has been shown that if the sample ion abundance is low, then the ion abundance range for the calibration file does not need to be exactly or closely matched, again benefiting the high throughput application. (c) 2005 American Society for Mass Spectrometry.