Mass spectrometric detection of keratins in tear fluid

Keratin contamination is a common problem in mass spectrometry proteomic analyses, particularly in bottom-up mass spectrometry. The purpose of this study was to determine the protein contaminants introduced during the proteomic analysis of tear fluid.Human tear fluid samples were collected using Schirmer strips. Proteomic analyses were performed using liquid chromatography–tandem mass spectrometry (LC-MS/MS) on blank Schirmer strips and tear fluid samples, with empty vials serving as controls for assessing environmental contaminant proteins.This study revealed nine major contaminant keratins in the mass spectrometry analysis. Several other keratins were identified as constituents of tear fluid. Background subtraction is necessary for the accurate analysis of tear fluid using mass spectrometry.