A simple and sensitive method for the determination of melamine in milk by first derivative UV spectrophotometry coupled with the H-point standard addition method

Abstract

Based on first order derivative UV spectrophotometry coupled with H-point standard addition, a simple, rapid, sensitive and accurate method for the determination of melamine in milk was developed. The milk sample solution was precipitated with silica gel in hydrochloric acid, then the first order derivative UV spectrum of the supernatant obtained by centrifuging the precipitation solution was measured. The concentration of melamine in sample solutions was determined by the cross-point of two standard-addition curves obtained by plotting the difference (ΔdA/dλ) between the dA/dλ peak value at 229 nm and the dA/dλ valley value at 242 nm versus the added concentrations of melamine at two measurement acidity values of 0.75 mol L⁻¹ HCl and 2.5 mol L⁻¹ HCl, respectively. Under the optimum conditions, the relative standard deviation for three replicates of the milk sample and spiked sample was 4.94% and 3.41%, respectively. The recoveries for three kinds of milk samples were in a range of 95.5–113.3%. The proposed method can be applied to milk powder and liquid milk samples in which melamine contents are larger than 1.67 mg kg⁻¹ and 0.20 mg L⁻¹, respectively.