ESI-MS Analysis of Amino and Hydroxy Acids

ESI-MS data were collected using an Agilent 6130 single quadrupole mass spectrometer with a capillary voltage of 3.0 kV and a source fragmentation voltage of 70 V (lab frame). Samples were diluted to 1 mM (referring to the original amino acid and hydroxy acid concentration) and directly infused into the mass spectrometer using the following parameters: Binary running solvents: 95% H₂O, 5% acetonitrile with a flow rate of 0.5 mL/min. Injection volume: 5 μL with H₂O needle wash. Path length: 0.6 cm. Scan range: 65–2000 m/z. MS data were processed using a suite of macros in Igor Pro-8.0 [33 (link)]. All peak assignments correspond to [M-H]⁻ ions.