Simultaneous smartphone-based colorimetric determination of melamine and sodium hypochlorite in milk samples using a simple microfluidic kit

This research introduced a microfluidic kit for rapid and economic detection of melamine (MLM) and sodium hypochlorite (NaOCl) in milk samples. The kit allows for simultaneous identification of MLM and NaOCl by reacting with cyanuric acid-modified Au nanoparticles (Au@Ca) and N, N-diethyl-p-phenylenediamine, respectively. The resulting color changes are used as the analytical signal for detection. All of the effective operational parameters were optimized by a one-factor-at-a-time approach. Under the optimum conditions (pH 6.5, path length = 50 mm, flow rate = 0.1 ml/min) a linear relationship between the concentrations of MLM and NaOCl and the blue component of the analyzed RGB pixels of the images captured with a smartphone camera was observed. The linear ranges for MLM and NaOCl were obtained in the concentration ranges of 0.1–1 and 0.1–4.5 µM, respectively, with 0.040 µM and 0.078 µM detection limits, consecutively. The results indicate that the proposed microfluidic kit provides strong selectivity and high reproducibility for detecting MLM and NaOCl in milk samples. To validate the performance of the method, the microfluidic kit was employed for analyzing five different milk samples, yielding recovery values between 94.0% and 105.0% and relative standard deviation values lower than 4.12% indicating the proposed system has admissible accuracy for both analytes. Besides, the results were compared to those obtained using high-performance liquid chromatography, as a standard reference method, and a good agreement between the two approaches was found.