DETERMINATION OF ELEMENTAL COMPOSITIONS FROM MASS PEAK PROFILES OF THE MOLECULAR ION (M) AND THE M+1 AND M+2 IONS

The relative abundances of M + 1 and M + 2 ions help to identify the e lemental composition of the molecular ion (M). But scan speed, sensiti vity, and resolution limitations of mass spectrometers have impeded de termination of these abundances, Mass peak profiling from selected ion recording data (MPPSIRD) provided faster sampling and enhanced sensit ivity, which permitted use of higher resolution, M + 2 profiles having only a few percent of the ion abundance of M were monitored at 20 000 resolution. The relative abundances, exact masses, and shapes of M, M + 1, and M + 2 mass peak profiles were determined, By applying five c riteria based on these quantities, elemental compositions were determi ned even for ions too large (up to 766 Da) to be uniquely assigned fro m their exact mass and accuracy limits alone, A profile generation mod el (PGM) was written to predict these resolution-dependent quantities by considering all M + 1 and M + 2 ions for each candidate composition , The model also provided assurance that no other compositions were po ssible, Characterization of the M + 1 and M + 2 profiles by MPPSIRD an d the PGM greatly expanded the practical ability of high-resolution ma ss spectrometry to determine elemental compositions.