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A new approach for photometric measurements in procedures involving liquid–liquid extraction is proposed.

An environmental friendly procedure was developed for fast melamine determination as an adulterant of protein content in milk. Triton X-114 was used for sample clean-up and as a fluorophore, whose fluorescence was quenched by the analyte. A linear response was observed from 1.0 to 6.0mgL(-1) melamine, described by the Stern-Volmer equation I°/I=(0.999±0.002)+(0.0165±0.004) CMEL (r=0.999). The detection limit was estimated at 0.8mgL(-1) (95% confidence level), which allows detecting as low as 320μg melamine in 100g of milk. Coefficients of variation (n=8) were estimated at 0.4% and 1.4% with and without melamine, respectively. Recoveries to melamine spiked to milk samples from 95% to 101% and similar slopes of calibration graphs obtained with and without milk indicated the absence of matrix effects. Results for different milk samples agreed with those obtained by high performance liquid chromatography at the 95% confidence level.