For mixtures like these peptides, the mini-CIT system offers a simple and inexpensive alternative to a large commercial instrument such as the Synapt G2. The miniature MS system can provide useful mass spectral information for label-free detection and identification of chemical species. Sample mass spectra of bradykinin for both MS systems acquired during the CE separations are shown in FIG. 17. Some similar features can be observed in the two spectra, most notably the (M+2H)2+ peaks at 531 m/z. The most obvious difference is the observed peak width (12.0 m/z with mass spectrometer; 0.026 m/z with Synapt G2). Wider peaks are expected in the mini-CIT system due to high pressure operation and air buffer gas. Peak widths have been significantly improved (<5.0 m/z) by increasing the operating drive frequency to 14.4 MHz and operating at lower buffer gas pressures. Despite the increased peak width, a mass spectrum combined with CE migration time provides sufficient information for identification of many chemical species, especially for an application where the goal is detection of known target analytes. FIG. 18 is a graph that illustrates MS sampling rates for the Synapt G2 and the mini-CIT/ES system (time versus normalized BPI, arbitrary units).
FIGS. 19A-19C are graphs of infusion-ESI mass spectral measurements of Amino Acid, Amino Acid Mixture and a peptide, respectively. FIG. 19A also illustrates data from mass bank of the amino acid (Histidine) for comparison.
