Dipotassium phosphate k2hpo4

TBBPA (0.25 g, 99.0%) and the internal standard of d₁₀-TBBPA (100 μg mL⁻¹ in acetonitrile, 98.5%) were obtained from Dr. Ehrenstorfer GmbH (Augsburg, Germany). TBBPA DME (50 μg mL⁻¹ in nonane, ≥98%), surrogate standards of [¹³C₁₂]TBBPA (50 μg mL⁻¹ in methanol, 99%), and [¹³C₁₂]TBBPA DME (100 μg mL⁻¹ in toluene, 99%) were all purchased from Cambridge Isotope Laboratories, Inc. (Andover, MA). Methyl iodide (CH₃I, ≥98%), monopotassium phosphate (KH₂PO₄, ≥99%), dipotassium phosphate (K₂HPO₄, ≥99%), sodium hydroxide (NaOH, ≥96%), and sulfuric acid (H₂SO₄, 95–98%) were all obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Natural organic matter (NOM) from Suwannee River was bought from the International Humic Substance Society (Denver, CO). All solvents used in the study were of chromatographic grade and obtained from J. T. Baker (Philipsburg, NJ).
The working solutions of TBBPA and CH₃I used for methylation reaction were set at concentrations of 1 mmol L⁻¹ and 1 mol L⁻¹ in methanol, respectively. The working solution of CH₃I was prepared just prior to use. Ultrapure water (18.2 MΩ cm⁻¹) was produced by a Milli-Q (Billerica, MA) advantage A10 system. Natural river water (pH 6.8) without detectable TBBPA and its methylation products was sampled from the Qinghe River, Beijing, China, and stored at 4 °C before use.