2.1. Standards and Reagents
HT
ROTH
HT, Ole, HVA, and DOPAC (all purity ≥ 98%) were from Cayman Chemical (Ann Arbor, MI, USA). Pure HT-3-S (98%) was supplied by ChemCruz (Huissen, The Netherlands); Tyr (purity ≥ 99.5%) was from Sigma-Aldrich (Taufkirchen, Germany). HT-3-G (purity ≥ 97%) was from Biozol (Eching, Germany); citric acid, phosphoric acid, and L(+)-ascorbic acid were from Roth (Karlsruhe, Germany). Water, acetonitrile, methanol, acetic acid, and formic acid (all LC-MS-grade) were purchased from VWR Chemicals (Darmstadt, Germany).The liquid food supplements 