Fig. 1.

Mass spectrometric analysis of human tear fluid. This illustration shows a workflow overview of proteomic tear fluid examination. After tear fluid collection with a Schirmer Test strip and elution, protein concentration was determined by amino acid analysis. After that, an SDS gel (4–12% Bis-Tris) electrophoresis and staining followed. Then, protein lanes were fractioned, digested with trypsin and peptides extracted. Samples were again measured via amino acid analysis. In total, 48 fractions (12 per lane) were generated for nanoHPLC-ESI-MS/MS. (*modified image taken from http://planetorbitrap.com/, Thermo Fisher Scientific Inc., USA).