HPLC Determination of Preservatives in Food of Various Matrixes

The solid sample, e.g. cake, sausage and etc., (2.000 g) or liquid sample, e.g., drinks etc. (10.00 mL) was taken and diluted with some water. 2 mL of 220 g·L^-1 zinc acetate solution and 2 mL of 106 g·L^-1 potassium ferrocyanide solution were added to precipitate protein and to remove it by centrifuge. In case of semi-solid sample, e.g., jelly, 2.000 g were taken and diluted with water. The acidity was adjusted to pH 7 to 8 with ammonia (1+1) solution. The sample solution described above was made up to 25.0 mL with water, and separated by HPLC using TSK Eclipse XDB-C₁₈ column as stationary phase and mixed solution of methanol and triethylamin (1+9) (pH 5.0) as mobile phase. Linear relationships between values of peak area and mass concentration of benzoic acid and sorbic acid were found in the same range of 0.1-10.0 mg·L^-1, with detection limits (3S/N) of 1.8, 1.2 mg·kg^-1, respectively. Test for recovery was made by standard addition method at 3 concentration levels, giving results in the range of 90%-97%, with RSDs (n=6) less than 10%.