2.1. Chemical reagents
The chemical reagents used in this study (l-lysine monohydrochloride, pyridine, and sodium hydroxide) were obtained from Sigma-Aldrich (USA). The derivatization reagent, ethyl chloroformate (ECF), was purchased from Fluka (Japan). NaHCO3 was purchased from Samchun (Korea). Methanol and chloroform were obtained from Fisher (Korea). Triton X-100 and sodium phosphate (Monobasic and dibasic, anhydrous) were purchased from Biosesang (Korea).