Catalytic Kinetic Photometric Determination of Trace Amount of Melamine in Dairy Products

It was found that in H3PO4-KH2PO4 buffer solution,the oxidative coloration of 4-amino antipyrine by potassium ferricyanide was catalyzed by the presence of trace amount of melamine, and that linear relationship was kept between the magnitude of increase in absorbance (ΔA) and mass concentration of melamine in the range of 0.4-2.4 mg·L-1 as measured at 510 nm, the absorption maximum of the colored product. Based on these facts, a catalytic kinetic photometric method for determination of trace amount of melamine in dairy products was proposed. The optimized conditions found for the color reaction were as follows: ① amount of 20 g·L-1 4-amino antipyrine solution used: 2.5 mL; ② temperature of reaction: 70 ℃; ③ time of reaction: 4 min. Detection limit (3s) found was 0.313 mg·L-1. Using pure fresh milk as matrix, test for recovery was made by standard addition method, giving values of recovery in the range of 98.6%-101% and RSD′s (n=6) in the range of 0.13%-0.69%.