Detection of Melamine in Milk by Polarography

In a B-R buffer solution of pH 6.5, a sensitive polarographic reduction peak given by fluorescence (FRS) was observed, and the reduction peak current was lowered upon addition of melamine (MLM). It was shown that significant correlationship was held between amount of co-existing melamine and the decrease of reduction peak current. Based on these facts, a polarographic method applied for determination of MLM in milk was proposed. 0.2 mol·L^-1 B-R buffer solution (pH 6.5, 7.5 mL), 1.0×10^-4 mol·L^-1 FRS solution (2.5 mL) and definite amount of MLM standard solution or appropirate amount of sample solution were added successively to a 25 mL colorimetric tube and the mixed solution was diluted to mark with water. After thorough mixing, the solution was heated for 15 min at 45℃. The decrease of reduction peak current of the reaction system comparing with blank solution was measured by polarography. Linear relationship between values of decrease in peak current and mass concentration of MLM was obtained in the range of 1.0×10^-7-1.0×10^-5mol·L^-1, with detection limit (3s/k) of 5.1×10^-8mol·L^-1. Values of recovery were in the range of 91.2%-99.1%. Values of RSDs (n=10) were less than 1.0%. As shown by the results of linear sweeping polarography, the polarographic wave given by FRS at the electrode is irreversible reductive adsorptive wave and the electroactive compound is RFS.