Hclo4

Acesulfame potassium (98%) was purchased from Adamas Reagent Co., Ltd. (Shanghai, China). Potassium peroxymonosulfate (PMS) and humic acid (HA) were American Chemical Society (ACS) reagent grade and were obtained from Sigma-Aldrich (San Francisco, CA, USA). 5,5-dimethyl-1-pyrroline N-oxide (DMPO) (98%), ${\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7·10{\mathrm{H}}_2\mathrm{O}$ (99.5%), and ${\mathrm{H}}_3{\mathrm{BO}}_3$ (ACS reagent, 99.5%) were ordered from J&K Scientific (Beijing, China). Indigo carmine (90%) and ${\mathrm{NaNO}}_2$ (99%) were analytical reagent and traceable to Aladdin (Shanghai, China). HClO₄ (70–72%) and ethanol (HPLC grade) were ordered from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ammonium acetate, tert-butanol (TBA), NaOH, NaHCO₃, NaCl were all analytical-reagent and traceable to Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). High-performance liquid chromatography (HPLC)-grade methanol was obtained from Fisher Scientific (Waltham, MA, USA). Ultrapure water (18.2 MΩ⋅cm) was used to prepare solutions. Four natural water samples were collected from different cities of Zhejiang province (China). The water samples were dechlorinated before use.
HA stock solution was prepared in a procedure similar to that described in our previous work [45 (link)]. The accurate concentration of the HA stock solution was calibrated using a total organic carbon (TOC)-VCPH analyzer (Shimadzu, Japan).