High-throughput analysis of melamine in milk products with isotope dilution LC-MS/MS

An isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS) has been used for high-throughput detection of melamine in various milk products. The deployment of the new methodology in the context of the various international screening campaigns led by Joint FAO/IAEA Centre of Nuclear Techniques in Food and Agriculture, in which The University of Manchester (UK) is taking part, has been carried out in Bangladesh, Oman, and Sri Lanka. The isotope dilution that employs the use of isotopically enriched (13C & 15N) melamine as an internal standard has been demonstrated to be a robust approach allowing for the elimination of otherwise considerable matrix effects and pushing the sensitivity down to ppb-level (detection limit of 10 ppb has been demonstrated for a standard affordable table-top equipment capable of multiple reaction monitoring with precision of 2-5%). The analysis of milk (liquid and powders, milk-based baby formula and various health drinks) both locally produced and imported products, reveals most samples contain a detectable amount of melamine. The concentrations usually did not exceed 1 mg/kg, however, in several samples concentrations of up to 46 mg/kg were detected. Although these elevated melamine levels are still below (600-2500 mg/kg) reported during the melamine crisis of 2008 during which exposure to melamine-contaminated milk sadly led to many cases of renal failure, especially in infants and children, these levels are still concerning as they are hardly can be explained by purely background contamination.