Determination of Melamine Based on the Formation of an Insoluble Copper-Melamine Complex and Flame Atomic Absorption Spectrometry

A copper-melamine complex was optimally synthesized by heating excess copper(II), as 50 m mol L^?1 copper(II) chloride in 50% (v/v) methanol, and melamine at 80°C. The amount of residual copper(II) in solution after removal of the copper-melamine complex was then measured by flame atomic absorption spectrometry. The concentration of depleted copper was proportional to the concentration of melamine, with a linear calibration curve (melamine concentration against copper absorbance) between 0.5 and 2.5 m mol L^?1 (R² = 0.9943) and with a limit of detection of 0.50 m mol L^?1. Although external standard calibration provided poor recoveries in fortified fish flesh (40% to 74% for 5 to 10 mg melamine/g), the method of standard addition provided acceptable values (90% to 93%), with a relative standard deviation of 3% to 10%. The results obtained with the standard addition method were in broad agreement with those obtained by high performance liquid chromatography.