Validation of a rapid method of analysis using ultrahigh-performance liquid chromatography - tandem mass spectrometry for nitrogen-rich adulterants in nutritional food ingredients

• LC-MS/MS based method for the analysis of 9 economic adulterants in 6 protein rich ingredients.
• Use of stable labelled internal standards to achieve accurate quantitation.
• High-throughput analysis based sample preparation scheme.
• Comprehensive method validation to establish method suitability for routine use.

A method for the rapid quantification of 9 potential nitrogen-rich economic adulterants (dicyandiamide, urea, biuret, cyromazine, amidinourea, ammeline, amidinourea, melamine, and cyanuric acid) in five milk and soy derived nutritional ingredients, i.e. whole milk powder, nonfat dry milk, milk protein concentrate, sodium caseinate, and soy protein isolate has been developed and validated for routine use. The samples were diluted tenfold with water followed by treatment with 2% formic acid and acetonitrile to precipitate proteins. Sample extracts were analyzed using hydrophilic interaction chromatography and tandem mass spectrometry (HILIC-MS/MS) under both positive and negative modes. Stable isotope labeled internal standards were used to ensure accurate quantification. In multi-day validation experiments, the average accuracies, relative standard deviations (RSD), and method detection limits (MDL) for all analytes in whole milk powder were 82–101%, 6–13%, and 0.1 mg/kg–7 mg/kg, respectively. The retention times of the analytes in matrix spiked controls were within ±0.06 min of the average retention times of the corresponding analytes in calibration standards. The validated method was proven to be rugged for routine use to quantify the presence of 9 nitrogen-rich compounds in milk and soy derived ingredients and to provide a defense from economically motivated adulteration.