Development and Validation of an Ultra-Sensitive UHPLC-MS/MS Method for Neonicotinoid Analysis in Milk

A very sensitive ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated for the quantitation of the most common neonicotinoids (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid) at trace levels in milk. Using fast and selective liquid-liquid extraction (LLE) starting from 0.5 mL of milk, lowest limits of quantitation (LLOQ) equal or lower than 10 pg/mL for all analytes were achieved. Precision and accuracy were evaluated at four different concentrations (5, 10, 500, and 10000 pg/mL) and ranged between 2 and 16% (RSD) and 77-125%, respectively. Extraction recoveries and matrix effects ranged between 64 and 76% and 88-98%, respectively. The method was applied to measure neonicotinoid levels in a series of conventional and organic Swiss milks as well as in human breast milk and commercial powdered milk. More than 90% of the samples tested positive for at least one neonicotinoid. However, all animal samples were far below the maximum residue limits authorized for human consumption with average total neonicotinoid levels of 16.1 +/- 13.1 pg/mL. Human breast milks and powdered milks contained similar amounts of neonicotinoids. Taken together, our results demonstrate the high prevalence of neonicotinoids in milk from all origins, albeit at levels considered to be safe for human consumption.