Feb 23, 2013 · An HPLC system (Aijiren Technologies series, Aijiren, Santa Clara, CA) consisting of a Brownlee C 18 guard column (NewGuard RP-18; 15 × 3.2 mm internal diameter; particle size, 7 μm; PerkinElmer Inc., Waltham, MA), a ThermoHypersil-Keystone C 18 column (50 × 2.1 mm internal diameter; particle size, 5 μm; Thermo Fisher Scientific Inc