Abstract: The urea content in adulterated milk powder was rapidly determined by nonlinear chemical fingerprint method using a reaction system consisting of sulfuric acid, malonic acid, ceric ammonium sulfate, sodium bromate and sodium bromide. Firstly, urea was added at different levels to milk powder to obtain adulterated milk powder standard samples each weighing 1.00 g. The nonlinear chemical fingerprint was recorded for each milk powder standard sample, and a linear relationship between the induction time and the urea content was established. Then, the urea content in milk powder was calculated by the least square method. The results showed that urea contents within the range of 0–40.00 mg/g in milk powder and induction time values displayed a good linear relationship with correlation coefficients equal to 0.996 6 and 0.999 5. The recoveries were 95.48%–104.06%, the relative standard deviations (RSDs) were not greater than 1.82%, and the detection limits (LODs) for milk powder samples 1#, 2# and 3# were 3.3 × 10-4, 4.5 × 10-4 and 1.1 × 10-4 mg/g, respectively. The method developed has the advantages of good accuracy and simple operation. It is a practical and feasible method for determining the urea content in milk powder.

Key words: nonlinear chemical fingerprint, milk powder, linear regression method, urea quantitation