User-defined Customization Through .mz Scripts. A short .mz script (a) opens each MS/MS spectrum within a given LC-MS acquisition and returns those scans that contain the phosphotyrosine immonium ion (m/z = 216). The tab-delimited multiplierz output is readily opened in Excel and (b) a histogram view facilitates rapid evaluation of enrichment efficiency. In this example, the majority of peptides in the heart of the LC gradient (~25 - 65 min.) contain phosphotyrosine residues as evidenced by the presence of an m/z = 216 immonium ion.