Effect of post-excitation radius on ion abundance, mass measurement accuracy, and isotopic distributions in Fourier transform ion cyclotron resonance mass spectrometry.

We report an evaluation of a modern Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) instrument to determine the general trend of post-excitation radius on total ion abundance, mass measurement accuracy, and isotopic distributions for internally calibrated mass spectra. The optimum post-excitation radius was determined using total ion abundance, mass measurement accuracy (MMA), and isotope ratios. However, despite the utility of internal calibration for achieving ultimate MMA, the internal calibrant ions were insufficient for compensating for sub-optimum ICR cell conditions. The findings presented herein underscore the importance of determining the optimal post-excitation radius in FT-ICR-MS to achieve high ion abundance (low limits of detection), high MMA, and valid isotopic distributions.