Development of a stir bar sorptive extraction method for analysis of ochratoxin A in beer

A new, simple, and sensitive method was developed for extraction of ochratoxin A (OTA) in beer combined with HPLC-fluorescence detector. Samples were extracted by stir bar sorptive extraction (SBSE) followed by liquid desorption using commercially available Twister EG-Silicone. The main parameters influencing SBSE, including phase ratio, extraction time, stirring speed, ionic strength, organic modifier, pH, temperature, desorption mode, desorption solvent, and desorption time were optimized. Under the optimal conditions, assay was performed on 4 mL of samples acidified at pH 1.5. The samples were extracted for 180 min at a stirring speed of 800 rpm followed by desorption of analyte using 1 mL methanol under sonication for 45 min. The extract was evaporated at 50 degrees C under a gentle nitrogen stream, then redissolved in 200 microL of methanol-water (50 + 50, v/v). After each use, the stir bar was cleaned by sonication in methanol for 30 min three times. The method provided good linearity of the calibration curve with coefficients of determination greater than 0.999. Recoveries of OTA were greater than 83% with RSD lower than 10%, and LOD of OTA in beer was 0.64 ng/L. This method was applied to determine OTA in 19 beer samples. OTA was detected in 12 samples (63%) in the range of 0.01-0.27 ng/mL.