Determination of melamine and related triazine by-products ammeline, ammelide, and cyanuric acid by micellar electrokinetic chromatography

In this study, micellar electrokinetic chromatographic (MEKC) methods were developed for the detection of traces of melamine and its related by-products (ammeline, ammelide, and cyanuric acid). Two on-line sample concentration steps namely reversed electrode polarity stacking mode (REPSM) and cation-selective injection (CSI) were used for improving the detection sensitivity. For REPSM, a borate-NaOH buffer (pH 10, 35 mM) composed of 60 mM SDS and 10% (v/v) methanol, was used as carrier electrolyte, and samples were prepared in an aqueous solution of 10 mM NaOH. In CSI, a phosphate buffer (pH 2, 50 mM) containing 41 mM SDS was used as the carrier electrolyte, and samples were prepared with an aqueous solution of 10 mM NaOH and a phosphate buffer (pH 2.0, 25 mM) in a volume ratio of 1:9. The results indicated that REPSM enhanced all analyte signals except for melamine, which could be concentrated only by the CSI. The detection limit was reduced from 1.7 mg L⁻¹ to 2.8 μg L⁻¹ for melamine by the optimal CSI step, and from 0.23-1.2 mg L⁻¹ to 2.4-5.0 μg L⁻¹ for the other three analytes by the optimal REPSM step. Tableware made of melamine and samples of flour were used as test samples, and the results indicated that the proposed MEKC methods can successfully determine contaminations from melamine. The study also indicated that when the plastic made of melamine was exposed only once to an acidic solution (acetic or phosphoric acid) at 80 °C for 30 min, melamine continuously leached out from the test sample even without any further treatment with an acidic solution.