HS-GC Determination of Sodium Diacetate and Propionate in Food with Pre-Column Derivatization

5.000 0 g of food sample were placed into a 50 mL volumetric, and 1 mL of 1.0 g·L^-1 butyric acid standard solution was added as internal standard. About 25 mL of water were added and the mixture was mixed vortically and extracted ultrasonically for 30 min to have the diacetate and propionate dissolved in water. After diluting to mark with water and mixing thoroughly, the mixture was filtered and 5 mL of the filtrate were transferred to the head-space flask. 2 mL of the mixture of H₂SO₄ and methanol (15+85) were added and the HS-flask was closed tightly with its cap. Derivatization was taken place in the HS-flask at 85℃ for 30 min. An aliquot of 1 mL of the solution in HS-flask was introduced into and separated on the DB-624 chromatographic column under the programed temperature elevation condition in the interval from 70℃ to 240℃. The analytes were determined by the H₂-FID. Linearity ranges of sodium diacetate and calcium propionate (expressed as propionic acid) were obtained in the same range within 200 mg·L^-1. And values of detection limits (3S/N) found for sodium diacetate and calcium propronate (expressed as propionic acid) were same as 0.01 g·kg^-1. 3 kinds of blank food samples were taken as matrixes, and tests for recovery and precision were made by standard addition method with 6 parallel determinations, giving values of recovery in the range of 95.1% to 105%, and values of RSDs (n=6) ≤ 5.0%. On the base of the 3 food samples, same amounts (0.50 g·kg^-1) of standard solutions of the 2 analytes were added, and the synthetic samples were analyzed by the present method and the method given in GB standards, giving results with good conformity and without significant deviation.