Trisodium citrate

Silver nitrate (AgNO₃, ≥99%) was purchased from Fluka. Ethylenediamine (≥98%), sodium borohydride (NaBH₄, ≥98%), 3-mercaptopropionic acid (MPA, 98%), sulfo-N-hydroxysulfosuccunimide (sulfo-NHS, ≥98.5%), and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, ≥99%) were purchased from Aldrich. Trisodium citrate (≥99%) and sodium hydroxide (NaOH, ≥98%) were purchased from Beijing Chemical Works. HBsAg, Hepatitis B e antigen (HBeAg), HBsAb1, HBsAb2 and bovine serum albumin (BSA) were purchased from H & R Bioscience Co., Ltd. Deionized water was purified by a Milli-Q system and the resistivity was 18.2 MΩ·cm.

All antimicrobial drug standards (≥97% purities) were obtained from Alta (Tianjin, China). MS-grade methanol, acetonitrile, formic acid (FA), ammonium formate, and HPLC-grade toluene were obtained from Fisher (Branchburg, NJ, USA). Analytical grade anhydrous Na₂SO₄, anhydrous MgSO₄, trisodium citrate, disodium citrate, sodium chloride (NaCl), and sodium acetate (NaOAc) were purchased from Beijing Chemical Plant (Beijing, China); A bonded C18 zirconia-coated silica (Z-Sep⁺) was obtained from Sigma (Osterode am Harz, Germany). Primary secondary amine (PSA) and octadecyl silane (C18) were obtained from Agilent Technologies (Santa Clara, CA, USA). Ultra-pure water was prepared by Milli-Q ultrapure water machine obtained from Millipore Corporation (Burlington, MA, USA).
Forty-three antimicrobial drug standards are listed in Table S1, including quinolones and sulfonamides. Usually, individual stock solutions of drugs were prepared in methanol or acetonitrile at 500−1000 mg/L concentrations. All stock solutions could be stored stably for six months in closed brown-colored volumetric flasks under −20 °C refrigeration conditions. The standard working solution was diluted with methanol to the desired concentration (stored at −20 °C and prepared once a month).