Improved liquid chromatography–mass spectrometry performance in quantitative analysis using a nanosplitter interface

Several pairs of analytes in plasma were investigated to demonstrate the successful utility of a novel interface in quantitative bioanalytical LC–MS and LC–MS/MS. Recently in our laboratory, an interface (the nanosplitter) was developed that allows the coupling of normal-bore liquid chromatography with microelectrospray mass spectrometry. The post-column concentric split minimizes turbulence and is shown to produce significant gains in the mass spectrometric signal. This configuration of the splitter allows sampling of the center portion of the parabolic HPLC plug, which maintains chromatographic integrity while producing high split ratios and effectively conserving nearly 99.9% of the sample. When utilizing a Finnigan mass spectrometer (with a heated capillary interface design), the signal gain with the nanosplitter ranged from 5 to 16 times the peak area obtained using the conventional interface without splitting. The linearity of the nanosplitter and conventional interface are shown to be comparable for all analytes tested. The nanosplitter was also fitted to a Sciex mass spectrometer and the results were compared to those from turbo ionspray. While in this case no significant signal improvement was observed, when normalized to the actual analyte mass introduced into the MS, the mass sensitivity was still increased 270-fold. The variations in signal gain utilizing the nanosplitter on instruments from different manufacturers reflect the inherent differences in the source designs while confirming the benefits of coupling high flow LC separations with low flow mass spectrometric detection.