Determination of Propionic Acid in Foods with Multiple Matrices by High Performance Liquid Chromatography with Water Leaching, Ether Extraction and Alkali Solution Reverse Extraction

In view of the shortcomings of poor matrix purification effect and long time consumption in the existing pre-treatment methods for detecting propionic acid in food, the research mentioned by the title was conducted. An aliquot (5 g) of sample was taken, and 30 mL of water was added. The mixture was vortexed for 5 min, and sonicated for 30 min. After cooling to room temperature, the acidity of the solution was adjusted to pH 7.0±0.5.The 0.6 mL of 183 g·L⁻¹ zinc acetate solution and 0.6 mL of 92 g·L⁻¹ potassium ferrocyanide solution were added, and the solution obtained was diluted to 50 mL by water. After mixing evenly and centrifuging for 5 min, 1.0 mL of supernatant was taken, and 40 μL of 1 mol·L⁻¹ phosphoric acid solution and 2.5 mL of ether were added. The mixed solution was vortexed for 5 min, and centrifuged for 5 min. The extraction process was repeated once, and the ether layers were combined. Then 1.0 mL of 0.025 mol·L⁻¹ sodium hydroxide solution was added, and the mixed solution was vortexed for 5 min, and centrifuged for 5 min. The lower phase was collected, and passed through a 0.45 μm nylon filter membrane. The filtrate was introduced into the high performance liquid chromatograph, and propionic acid was separated by gradient elution with a mixture (pH 2.6, adjusted by phosphoric acid) of methanol and 1.5 g·L⁻¹ diammonium hydrogen phosphate solution at volume ratio of 5∶95 as the mobile phase on Thermo Hypersil Gold C₁₈ column, and determined at wavelength of 214 nm. It was shown that linear relationship between values of the mass concentration and peak area of propionic acid was kept in the range of 0.01-0.5 g·L⁻¹, with detection limit (3S/N) of 0.03 g·kg⁻¹. Test for recovery was made at the 3 concentration levels on foods with multiple matrices by standard addition method, giving recoveries in the range of 84.8%-95.3% and RSDs (n=6) in the range of 2.8%-6.2%. The proposed method was used for the analysis of foods with multiple matrices, and absolute values of relative errors between detection results of the proposed method and the distillation method in GB 5009.120—2016 were not more than 10%.