A sensitive and validated method for determination of melamine residue in liquid milk by reversed phase high-performance liquid chromatography with solid-phase extraction

A sensitive and validated method for the determination of melamine residue in liquid milk is developed using reversed phase high-performance liquid chromatography-diode array detection (RP-HPLC-DAD) with solid-phase extraction (SPE). The conditions of the extraction, SPE and HPLC were investigated and optimized. The linearity is satisfactory in the range of 0.1–50 μg/mL with a correlation coefficient of 0.9998. Under the optimal conditions, the method limit of detection (LOD) and method limit of quantification (LOQ) were 18 μg/kg and 60 μg/kg, respectively. The recovery of melamine for milk samples spiked with 0.10–3 mg/kg was in the range of 85.5–99.3% with the RSDs (n = 3) of 2.3–3.7%. The intra-day assay precision (RSD) was 5.6% for five replicates of quality control milk sample at 2 mg/kg level. Confirmation of the identities of melamine was achieved by monitoring the two transitions in multiple-reaction monitoring (MRM) mode, and has been applied successfully for the determination of melamine residue in liquid milk samples. The confirmatory method can permit the detection of melamine residues at levels as low as 60 μg/kg in different liquid milks.