Development of a highly sensitive voltametric sensor for trace determination of melamine residues in milk and water samples

Melamine (MEL) is a key and broadly used trade chemical that is risky to human health and environment. Hence, a method comprising a preanodized glassy carbon electrode (GCE*) for sensitive analysis of MEL has been developed. The electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and surface area data confirmed the preanodization of the GCE. The results highlight the efficacy and the compatibility of the GCE* protocol for sensitive detection of trace levels of MEL. The method was based upon the indirect differential pulse voltammetric (DPV) sensing of MEL depending on its competition with uric acid (UA) as a recognition element at the surface of GCE*. The electrochemical oxidation of UA at GCE* showed one well defined anodic peak at 0.23 V vs. Ag/AgCl electrode. Under the optimized parameters, the linearity range of the method was calculated as 2.0 x 10(-9) -8.0 x 10(-9) M (0.252-1.009 mu g.L-1) with an accuracy of 99.21 +/- 5.02 (R-2 = 0.9969). The lower limits of detection (LOD) and quantization (LOQ) were 6.0 x 10(-10) M (0.075 mu g.L-1) and 2.0 x 10(-9) M (0.252 mu g.L-1), respectively. Intra-day and inter-day precisions of the method were in the range 98.46 +/- 5.02 and 99.21 +/- 5.84%, respectively. The average relative standard deviation (RSD) at 2.0 x 10(-7) M of MEL for successive measurements (n = 3) was +/- 3.0%. Analysis of MEL in milk powder and water samples determined using the developed DPV procedures gave satisfactorily recoveries ranged from 96.11 to 97.01% for low and high levels of MEL in a variety of milk samples with relative standard deviations (RSDs) over the range of +/- 4.1% 0.32%-3.61%. The method offered a significant improvement for trace determination of MEL in a variety of milk and milk powder samples in terms of efficient, rapid, economical, and miniaturized sample preparation methods, which yielded fewer matrix effects compared with SPE method. The established method is expected to be widely applied for analysis of MEL at trace levels in the future.