Determination of Benzoic Acid and Sorbic Acid in Soy Sauce, Vinegar and Carbonated Beverage by High Performance Liquid Chromatography Combined with Hollow Fiber Membrane Liquid Phase Microextraction

A method for determination of benzoic acid and sorbic acid in soy sauce, vinegar and carbonated beverage by high performance liquid chromatography (HPLC) combined with hollow fiber membrane liquid phase microextraction was established. 0.100 0 g of soy sauce, vinegar or ultrasonic degassed carbonated beverage sample was taken and 0.1 mL of internal standard (cinnamic acid) solution (500 mg·L^-1) was added, and made its volume up to 50 mL with water. The above sample solution of 10 mL was removed into extraction vial for adjusting pH to 2.5 with 1 mol·L^-1 hydrochloric acid solution, and 0.50 g of sodium chloride was added. The small segment (6.0 cm) of polyvinylidene fluoride hollow fiber membrane was washed with acetone and soaked in tributyl phosphate for 3 min by ultrasonic. The hollow fiber membrane cavity was injected with 50 μL of sodium hydroxide solution (pH 13.0), and immersed into the extraction vial after sealing to extract for 25 min at 1 000 r·min^-1. According to the working conditions of the instrument, the solution in the hollow fiber membrane was absorbed for HPLC analysis, and internal standard method was used for quantitative analysis. As shown by the results, linear relationships between mass concentrations of benzoic acid and sorbic acid and their peak area ratios of analytes to internal standard were kept in the range of 0.01-10.00 mg·L^-1, with detection limits (3S/N) of 0.001 mg·L^-1 and 0.003 mg·L^-1, respectively. Soy sauce sample was determined, and intra-day precision (n=6) and inter-day precision (n=6) were less than 3.0%. Recovery test was made on soy sauce samples at 3 concentration levels by standard addition method, giving results in the range of 95.5%-106%. This method has been applied for analysis of substantial samples, and benzoic acid and sorbic acid were detected in varying degrees.