Ffa d3 standard

CAP, TAP, FF, FFA, and CAP-D5 standards were obtained from Dr. Ehrenstorfer GmbH (Augsburg, Germany). FFA-D3 standard was obtained from Toronto Research Chemicals (Toronto, ON, Canada). HPLC-grade acetonitrile (ACN), methanol, ethyl acetate, and n-hexane were supplied by Merck (Darmstadt, Germany). Reagent grade ammonium hydroxide, HPLC-grade acetone, and formic acid were supplied by Sinopharm Chemical Reagent Co. (Shanghai, China). Water was purified with an Arium Pro ultrapure water purification system (Sartorius, Göttingen, Germany).

Standards of CAP, TAP, FF, FFA and CAP-D5 (purity ≥99.50%) were obtained from Dr. Ehrenstorfer GmbH (Augsburg, Germany). FFA-D3 standard (purity ≥99.50%) was purchased from Toronto Research Chemicals (North York, ON, Canada). HPLC-grade solvents, including methanol, acetonitrile (ACN), ethyl acetate and n-hexane, were supplied by Merck Company (Darmstadt, Germany). HPLC-grade acetone, formic acid and guaranteed reagent grade ammonium hydroxide were provided by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ultrapure water was supplied by the Sartorius-Arium pro system (Sartorius AG, Goettingen, Germany).
Individual standard stock solutions (1 mg/mL) of CAP, TAP, FF, FFA, CAP-D5 and FFA-D3 were prepared in methanol and stored at −20 °C for six months. CAP-D5 and FFA-D3 were used as internal standards. The combined standard working solution at a concentration of 10 μg/mL for each analyte was prepared by mixing equal volumes of the individual standard stock solution of CAP, TAP, FF and FFA with a concentration of 1 mg/mL and diluting with methanol. The mixed internal standard working solution at the concentration of 1.0 μg/mL was prepared by diluting the internal standard stock solutions (1 mg/mL) with methanol. The abovementioned standard working solutions were stored at −20 °C for up to three months.