Concentrated hydrochloric acid

We purchased standards for quercetin (purity=98.0%) and vanillic acid (purity=98.0%) from Shanghai Shidande Standard Technical Service Co., Ltd. (Shanghai, China). HPLC-grade methanol (purity≥99.9%) was purchased from Fisher Chemical (Waltham, USA). All water used in this research was double distilled. Other reagents and chemicals were all analytical grade. MgCl₂·6H₂O (purity≥98.0%), KCl (purity≥99.5%), NaCl (purity≥99.5%), CaCl₂ (purity≥96.0%), D-Glucose ([α]20D: +52.5° - +53.0°), NaHCO₃ (purity≥99.5%), NaH₂PO₄ (purity≥99.0%), concentrated hydrochloric acid (ω%36.0–38.0%), and acetic acid (purity≥99.5%) were supplied by Beijing Chemical Works (Beijing, China). Ethyl carbamate (trade name: urethane) was purchased from Tianjin Guangfu Fine Chemical Research Institute (Tianjin, China). Finally, 0.9% sodium chloride injection solution was obtained from Shijiazhuang Pharmaceutical Siyao Co., Ltd. (Shijiazhuang, China).

Sulfanilic acid was purchased from TCI (Shanghai) Development Co., Ltd., (Shanghai, China). Natural graphite flakes were purchased from Sigma-Aldrich (St. Louis, MO, USA). Sodium carbonate, concentrated hydrochloric acid, sodium borohydride, hydrazine (80%, N₂H₄·H₂O), and sodium nitrite were purchased from Beijing Chemical Works. Polyacrylonitrile (PAN, average Mw 150,000) was purchased from HuBei ChuShengWei Chemistry Co., Ltd., (Wuhan, China).

Natural graphite flakes (8,000 mesh, 99.95% purity), p-propylaniline, p-n-octylaniline, and p-n-dodecylaniline were supplied by Aladdin. Concentrated sulfuric acid (95–98%), concentrated hydrochloric acid (36–38%), potassium permanganate, and solvents used in this work were all analytically pure and purchased from Beijing Chemical Factory (China). Hydrogen peroxide (H₂O₂) and sodium nitrate were supplied by LaiYang Shi Kant chemical company. Cellulose ester membrane was supplied by Hangzhou Special Paper Co. Ltd.