Indirect determination of melamine by atomic spectrometry of excess copper(II) Ion

Abstract

The indirect atomic absorption spectrometric method was developed for the determination of melamine after forming complexes with excess copper(II) ions. The copper-melamine complex (Cu-Mel) was synthesized by constantly heating and stirring the solution of copper(II) and melamine. Parameters affecting the complex formation including types of copper salt, solvents, temperature, and curing time were investigated in order to optimize the conditions for analytical assay. The optimal conditions for the copper-melamine synthesis were the system of CuCl2 in methanol at 80 °C for 14 hours. The synthesized complex was characterized by X-Ray powder diffraction spectrometry, thermogravimetry, and Fourier transform infrared spectrometry. In addition, stoichiometric study by Job’s plot revealed 1:2 copper-melamine. The complexation reaction was first-order with respect to both copper and melamine, and the activation energy of the reaction estimated by Arrhenius equation was 19.60 kJ/mol. Flame atomic absorption spectrometry used for measuring the amount of copper remaining in the solution indicated that the amount of depleting copper was proportional to the amount of melamine. The calibration curve built between melamine concentration series and copper absorbance showed a linearity with the coefficient of 0.9943 and the limit of detection of 0.60 mM. The external standard and standard addition used for melamine determination in fish sample showed acceptable recoveries between 70-93% and 3.0-10% RSD.