Figure 1 of González, Mol Vis 2012; 18:1572-1582.

Figure 1. Mass spectrum of an unprocessed tear and a tear processed with solid-phase extraction (SPE) protocols. A: Direct analysis of a tear by MALDI-TOF MS produced a displacement of the baseline. This phenomenon is due to ion suppression produced mainly by the presence of salts and lipids. A limited peptide population can be noted. B: The same tear treated with four different SPE methods before MS analysis offers a spectrum which is more amenable for profiling analysis. MB C18: Magnetic Beads; EM C8: Empore Disc C8; EM C18: Empore Disc C18; ZT C18: Zip Tip.