Comparison of data quality for different lengths of exposure with equivalent dose. NSLS X28C 10 ms exposure (left) and ALS 8.3.2 30 ms exposure (right) are shown for two cytochrome c peptides. Unmodified spectra (extraction of peptide mass) are shown above the corresponding modified spectra (extraction of peptide mass + 16 corresponding to one oxidation event). Arrows indicate regions over which r.m.s. noise was calculated. Note that the quality of the mass spectra due to sample processing and instrument sensitivity also strongly impact the signal-to-noise (S/N) ratio.