Methodology Utilizing MS Signal Intensity and LC Retention Time for Quantitative Analysis and Precursor Ion Selection in Proteomic LC-MALDI Analyses

This study describes a methodology for performing relative quantitation in large-scale proteomic sample comparisons using an LC−MALDI mass spectrometry analytical platform without the use of isotope tagging reagents. The method utilizes replicate analyses of a sample to create a profile of constituent components that are aligned based on LC elution time and mass. Once components from individual runs have been grouped as common “features”, the Student's t test is used to determine which components are systematically different between samples. In this study, five HPLC runs of human plasma were compared to five HPLC runs of human serum. About 3889 components were detected in all 10 runs. Of these, 1831 corresponded to ∼100 known serum proteins, based on MS/MS analysis of one run each from serum and plasma. As expected, fibrinogen α, β, and γ chains accounted for many of the most significant differences. Therefore, using MALDI, samples containing thousands of peptides can be compared in a minimal amount of time. Moreover, the results of the comparison can be used to guide further MS/MS mode sample interrogation in a result dependent manner.