Application of sequential paired covariance to liquid chromatography mass spectrometry data - Enhancements in both the signal-to-noise ratio and the resolution of analyte peaks in the chromatogram

The algorithm of sequential paired covariance (SPC) has been previously reported to dramatically enhance the signal-to-noise (S/N) ratio for on-line separations combined with mass spectrometry. That initial study focused on a limited number of data sets derived from the combination of capillary electrophoresis (CE) with time-of-flight mass spectrometry using an electrospray interface. Results from the initial study clearly demonstrated that a significant enhancement (almost two orders of magnitude) in the S/N ratio of the eluting peaks in the electropherogram could be obtained, facilitating identification of the analytes. In this report, the algorithm has been applied to liquid chromatography-mass spectrometry data obtained on a triple quadrupole instrument and we have evaluated the general applicability of the SPC approach to several types of microcolumn separations with mass spectrometric detection, including CE coupled with Fourier transform ion cyclotron resonance mass spectrometry. In all the cases we tested, we found the algorithm enhanced the S/N ratios of the resulting chromatograms or electropherograms to a similar extent. This report further demonstrates the SPC approach to enhance the resolution as well as the S/N ratio of the eluting peaks of a complex peptide mixture. While many variations of the algorithm are possible, we have also found higher order covariance (e.g., 3rd order) is useful for eliminating coincidental noise in sequential mass spectra, giving the potential to extract broad, low intensity analyte peaks. We also demonstrate the sequential covariance approach for enhancing the SIN ratio of mass spectra.