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.