2.2. Chemicals and instrumentation
AFM1 standard was purchased from Sigma–Aldrich Chemical Co. (St. Louis, MO, USA). Standard solutions of AFM1 were prepared and standardized by spectrophotometer in accordance with AOAC (2005, chap. 49). Calibration curve was prepared by dilution of working standard solutions in water:acetonitrile:methanol (65:25:10, v/v/v) covering the range of 0.004–2.5 μg/L. Acetonitrile and methanol were HPLC grade and all other chemicals were analytical grade. Ultrapure water was generated by a Milli-Q Millipore system (Massachusetts, USA).