Uniformity of ionization response of structurally diverse analytes using a chip‐based nanoelectrospray ionization source

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Abstract
The major drawback of liquid chromatography/mass spectrometry (LC/MS) for the analysis of mixtures is the non‐quantitative nature of these studies. The ionization efficiency of the various components in the mixture (e.g., a compound and its metabolites) can vary greatly and, therefore, relative intensities of signals cannot be related to relative abundance. A chip‐based nanoelectrospray ionization source was used to compare the ionization efficiencies of compounds with different physical‐chemical characteristics. The data indicate that the ionization efficiencies vary much less with the chip‐based device than by LC/MS. This was ascribed to the generation of a much higher electric field around the nozzles, which supplies a large excess of protons to the small droplets and reduces/eliminates the differences in the ionization efficiency for the analytes. Copyright © 2005 John Wiley & Sons, Ltd.