Multiplex multidimensional nanoLC-MS system for targeted proteomic analyses

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Abstract
The present work describes a dual‐column and dual‐sprayer LC‐MS system for high‐throughput proteomic analyses. This system consists of two precolumns for sample desalting and two analytical columns. Each column is terminated by a nanoelectrospray emitter mounted on a robotic arm enabling their sequential positioning in front of the sampling cone of the mass spectrometer. The effluent from each emitter is recorded in separate acquisition channels without detectable crosstalk. Gradient elution to both nanoLC columns is delivered by a single HPLC system via a flow splitter. The reproducibility of retention time and peak intensity of the present multiplex system were comparable to those obtainable using a single emitter configuration. Replicate injections of complex tryptic digests (n = 10) indicated that this system provided good reproducibility of retention time and peak intensity on both columns with RSD values of less than 0.9 and 18.6%, respectively. The application of this system is demonstrated for the monitoring of protein expression changes in U937 human monocyte cells with and without phorbol ester administration. Furthermore, we also demonstrated the use of this multiplex system in a 2‐D LC configuration to increase sample loading and throughput for the analysis of biomarker samples of higher complexity. Variations in peptide abundance down to two‐fold change were identified across salt fractions for spiked tryptic digests present at a level of 50 fmol in 1.5 μg of plasma samples.