A typical LC-MS chromatogram of three standard peptides. (a) 4 pmol of Angiotensin III, Fibrinopeptide B, and Angiotensin I were mixed and analyzed by LC-MS/MS 10 times. (b–d) Intensity of Angiotensin I, Fibrinopeptide B, and Angiotensin I at mean m/z 449.49, 786.24, and 433.23 Da from 10 injections was calculated, respectively. Their CVs are 15.0%, 11.4%, and 63.4%, respectively. Also, Figures (b–d) show that identical amounts of peptides generate totally different peak area, and the fold difference is as large as 7.45 ().