Updated FTP location. To measure quantification accuracy, we generated two proteome samples of E.coli and human cell lysate. E.coli tryptic peptides were tagged with four different labels of reporter ions (m/z: 114, 115, 116 and 117). These labeled peptides were mixed at the following ratios: 114:115 = 10:1, 114:117 = 5:1, 114:116 and 117:115 = 2:1, and 116:117 = 2.5:1. Human tryptic peptides were tagged with two different labels of reporter ions at 114 and 115, and these samples were mixed 1:1.