Trifluoroacetic acid (TFA) is a commonly used mobile phase additive in liquid chromatography-mass spectrometry (LC-MS)-based biopharmaceutical characterization to enhance reversed-phase chromatographic performance of peptide separation; however, it leads to significant mass spectrometry signal suppression during electrospray ionization. Previous studies have shown that introducing large amounts of carboxylic acids or ammonium hydroxide to LC eluents postcolumn can improve MS sensitivity. In this study, we discovered glycine as a simple additive for TFA mobile phases, which mitigates ion suppression through a similar mechanism but in a more effective way than weak acid or weak base and boosts mass spectrometry responses (signal-to-noise ratio) of peptides by more than 1 order of magnitude on average after directly adding a small amount (e.g., 2 mM) into TFA mobile phases without compromising the chromatographic performance of peptide separation. Other small molecule additives in TFA mobile phases, such as amino acids containing extended side chains with different chemical properties and glycine-based variants, were also evaluated. The results demonstrated that glycine offered the best response boosting on peptides. The discovery of this glycine additive in TFA mobile phases provides a simple and conventional approach to achieve greater mass spectrometry detection sensitivity than TFA mobile phases for LC-MS-based characterization of biopharmaceuticals.