Figure 2.

Use of different salts for separation of tryptic peptides with either Asp or pSer at the same sites. Peak identities were confirmed by running the standards individually. Key to peptide standards: per insert. Column: PolyWAX LP, 200 × 4.6 mm; 5 μm, 300 Å. Flow rate: 1 mL/min. Detection: 280 nm. (A) ERLIC with ammonium formate: Mobile Phase A: 20 mM ammonium formate, pH 2.2, with 70% ACN. Mobile Phase B: 1 M ammonium formate, pH 2.2, with 10% ACN. Gradient schedule: 0–5′, 0% B; 5–35′, 0–100% B. (Note: Standard 2P was run separately from the others under identical conditions). (B) ERLIC with Na-MePO₃: Mobile Phase A: 20 mM Na-MePO₃, pH 2.0, with 70% ACN. Mobile Phase B: 300 mM TEAP, pH 2.0, with 10% ACN. Gradient schedule: 0–5′, 0% B; 5–48′, 0–100% B.