Optimization of RP-HPLC Determination of Melamine in Milk Powder

The RP-HPLC method for determining melamine in milk powder has been developed. However, the differences in chromatography instrument and column performance and status may lead to the occurrence of disagreement among determina- tion results from different labs. To enhance the accuracy, reproducibility and efficiency of melamine detection by HPLC, sample preparation and chromatographic conditions were optimized in the present study. Milk powder samples were extracted using 1% trichloroacetic acid and 2% lead acetate solution in an ultrasonic field and cleaned up on an SCX solid phase extraction column which was activated and leached using 1% trichloroacetic acid instead of water. The optimization of chromatographic conditions was achieved by increasing the ion-pairing buffer containing 10 mmol citric acid and 10 mmol heptane-1-sulfonic acid sodium salt to pH 3 and adjusting the proportion of acetonitrile in the mobile phase consisting of it and the ion-pairing buffer to 28% (V/V). The external standard method was adopted for the quantitative analysis of melamine. The correlation coefficient of linear equation was 0.9997 and the limit of detection of melamine was 0.15 mg/kg by this method. The recoveries for melamine in blank milk powder spiked at five levels were within 95.8%-101.5%. The optimized method has high reproducibility and allows accurate detection and high recovery for melamine in milk powder.