Bisphenol a d16

Chemicals used in the YES and standard substances in the chemical analysis were purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO USA): Chlorophenol Red-β-D galactopyranoside (CPRG), 17β-estradiol (E2), nonylphenol (NP), octylphenol (OP), bisphenol A (BPA), bisphenol A-d₁₆ and diethylstilbestrol (DES). All reagents of HPLC grade used for sample processing and analysis (methanol, dichloromethane, n-hexane and acetone) were obtained from J.T.Baker Avantor Co. (Center Valley, PA, USA). Glass fiber filters (GF/F, pore size 0.7 μm) were obtained from Whatman (Maidstone, UK) and prebaked at 450 °C for 4 h prior to use. Deionized organic-free water was obtained from a Milli-Q water purification system from Millipore (Bedford, USA). The solid-phase extraction sorbent Sep-Pak C18 vac cartridge (1000 mg, 6 cc) was supplied by Waters Co. (Milford, MA, USA). Stock solutions of the four phenols were prepared in methanol at 1 μg/μL and stored at −20 °C for later use; the appropriate working standard solutions were prepared in methanol and stored in amber glass bottles at 4 °C.