Hollow-fiber liquid-phase microextraction combined with high-performance liquid chromatography for analysis of melamine in milk products

A novel liquid-phase microextraction (LPME) technique, based on a hollow fiber (HF), in conjunction with high-performance liquid chromatography, has been developed for analysis of melamine in milk products. Melamine was extracted directly from milk products by use of a hollow-fiber membrane filled with organic solvent. HFLPME conditions, for example pH, extraction solvent, temperature, stirring rate, and extraction time were optimized. The best extraction efficiency of melamine was achieved under the conditions: pH 9.5, 35 μL n -octanol as extraction solvent, temperature 55°C, stirring rate 300 rpm, and extraction time 30 min. The HF-LPME technique resulted in a preconcentration ratio of 29-fold. Baseline chromatographic separation of melamine was achieved on a C 18 column with 96:4 ( v / v ) 0.02 mol L -1 ammonium sulfate-methanol as isocratic mobile phase. The linearity of the method ranged from 1.0 to 100.0 μg mL -1, correlation coefficient 0.9994. The limit of detection by use of HF-LPME was 0.021 μg mL -1 at a signal-to-noise ratio of 3. The optimized HF-LPME technique was successfully applied to the analysis of melamine in milk products collected from different commodity manufacturing units.