Combining low and high mass ion accumulation for enhancing shotgun proteome analysis by accurate mass measurement

A simple procedure is described that increases sensitivity and dynamic range for the analysis of a proteome batch digest by FT-ICR mass spectrometry. Ions at the low and high mass ranges are preferentially collected using two different sets of tuning conditions. By combing data collected using tuning conditions that favor low mass (m/z < 2000) and high mass (m/z > 2000) ions, 277 proteins are identified for a whole cell lysate of Methanococcus maripaludis in a single HPLC-MALDI FT-ICR mass spectrometry experiment, a 70% improvement compared with previous analyses using a wide mass range acquisition. This procedure improves the detection of low abundance ions and thereby increases the range of proteins that are observed. Because the observed mass range is effectively narrower for each spectrum, mass calibration is more accurate than for the standard method that provides a wide range of masses. The trap plate potential on the analyzer cell may be set to a higher value than used for wide mass range measurements, increasing the ion capacity of the analyzer cell and extending the dynamic range, while still maintaining mass accuracy.