Some second-order errors in average mass measurement of complex biological molecules in time-of-flight particle desorption mass spectrometry

Abstract

The reasonable criterion of sufficiency of data collection was shown for time-of-flight (TOF) particle desorption mass spectrometry with a single ion counting registration system: 1000–2000 counts should be collected in the peak (for complex molecules, such as bovine insulin, mol. wt. 5733.6 u). In this case, providing that all counts in the peak are measured, the standard deviation from the real average mass, due to the statistical error in measuring the isotopic distribution centroid, is within the range 0.03–0.07 u. However, if the centroid is calculated using only those counts above a given level relative to the peak base, an error of ca. 0.5 u or more is produced; the size of the error depends mainly on the magnitude of the height level of the centroid measurement. This is true for the molecules with masses greater than 700 u. Correction values to the peak centroid measured at a certain level are given. The validity of corrections was proved experimentally using a MSBX TOF mass spectrometer with a 252Cf ion source.