Manganese sensitised-indirect determination of melamine in milk-based samples by flame atomic absorption spectrometry coupled with ultrasound assisted-cloud point extraction

Abstract

ABSTRACTIn the current study, a simple and low- cost method of UA-CPE in combination with flame atomic absorption spectrometry (FAAS) was developed for pre-concentration and indirect determination of melamine in milk-based samples. The method is based on the formation of charge transfer sensitive ternary complex among melamine, Mn(II) and Eosin Yin presence of sensitivity enhancer, ionic surfactant cetyltrimethylammonium bromide at pH 4.5, and then extraction of the formed complex into the micellar phase of nonionic surfactant, Triton X-114. After extraction, the surfactant-rich phase was diluted with 1.0 mol L−1 HNO3 in methanol and aspirated into the nebuliser of FAAS for indirect analysis. For optimisation of the variables affecting the ion-pair formation and extraction efficiency, the univariate method was adopted due to its simplicity and ease of use. Under optimal conditions, a good linear relationship was observed from 0.8 to 130 µg L−1 with a detection limit of 0.23 µg L−1. From pre-concentration of 35-mL sample, a pre-concentration factor of 70-fold was obtained with a good sensitivity enhancement (88.5). The accuracy and precision were evaluated as repeatability and intermediate precision with RSD of less than 6.5% with a recovery varied from 92.5% to 98.6%. (n: 5, 5, 25 and 100 µg L−1). The performance of the method from the accuracy and precision studies of two quality control samples was highly good with the precision (4.2–6.0%) and relative recoveries (91.4–96.0%) obtained for spiking levels, 5 and 10 µg L−1. The accuracy, according to two-way ANOVA analysis, was also controlled by two calibrations approaches without any matrix effect in analysis step of samples.