Exact mass determination of narrow electrophoretic peaks using an orthogonal acceleration time-of-flight mass spectrometer

High efficiency electrically driven separation techniques, such as capillary zone electrophoresis (CZE) and capillary electrochromatography (CEC), yield narrow peak widths of the order of a few seconds. Scanning instruments may have difficulty in obtaining sufficient data points across such narrow peaks (although the use of selected ion monitoring (SIM) mode may overcome this). Orthogonal acceleration time-of-flight ((oa-TOF)) mass analysers have an inherent ability for fast acquisition rates allowing a high number of data points (for example 10 spectra s−1) to be collected across a narrow peak and are capable of operation at resolutions in the region of 5000 full width half maxima (FWHM). This enables spectral data to be measured with accuracies greater than 5 ppm, allowing the molecular formula to be predicted / confirmed. We have investigated the use of an oa-TOF mass analyser coupled to CZE. The on-line separation of a drug substance and related impurities has been achieved. Copyright © 1999 John Wiley & Sons, Ltd.