Subpicogram Determination of Melamine in Milk Products Using a Luminol−Myoglobin Chemiluminescence System

A sensitive chemiluminescence method based on a luminol−myoglobin system is proposed for the determination of melamine in milk products. It was found that the mixed solutions of melamine and myoglobin could react to form a complex on line, which could greatly inhibit the chemiluminescence intensity generated from the reaction between luminol and myoglobin. The decrease in chemiluminescence intensity was proportional to the concentration of melamine, giving a calibration graph linear over the concentration from 10 pg mL−1 to 50 ng mL−1 (R2 = 0.9988) with a detection limit of 3 pg mL−1 (3σ). At a flow rate of 2.0 mL min−1, one analysis cycle, including sampling and washing, could be accomplished in 20 s with a relative standard deviation of <4.0%. The proposed method was applied successfully to the determination of melamine in milk products, and the recovery was from 93.4 to 106.5%. The possible mechanism of luminol−myoglobin−melamine reaction is given.