Abstract

This paper describes an analytical workflow for the detection of dicyandiamide and other nitrogen rich compounds in milk and other protein-rich foods. Food samples were extracted using a simple liquid extraction followed by extensive dilution to minimize possible ion suppression effects ionisation. Liquid chromatography (LC) separation used a normal phase gradient on a hydrophilic interaction chromatography (HILIC) column followed by tandem mass spectrometry (MS/MS) detection. Two selective multiple reaction monitoring (MRM) transitions were detected for each target analyte using the ratio of quantifier and qualifier ion for identification. The sensitivity of the LC-MS/MS system allowed the quantitation of dicyandiamide and other nitrogen rich compounds in milk and other protein-rich foods with limits of quantitation down to low μg/kg. Dicyandiamide was quantified in milk with a limit of quantitation of less than 1μg/kg after 200x dilution of the sample extract. Recovery was determined to be 97.3% with a relative standard deviation of 3.66%.

INTRODUCTION

Recent issues with adulteration of food using nitrogen rich compounds to make the protein content of food appear higher than the actual value highlighted the need for both food manufacturers and regulatory agencies to utilize fast and accurate analytical techniques to proactively ensure product safety. In 2007, melamine and cyanuric acid in wheat gluten added to pet food caused renal failure and sickened and killed large numbers of cats and dogs. In 2008, Chinese authorities discovered the adulteration of milk and infant formula with melamine by several Chinese producers. There were hundreds of thousands of victims and six confirmed deaths in China, as well as product recalls in many countries. (1-4)
In response to the melamine contamination a large number of analytical methods were developed for the detection of melamine and its analogues, including several published by the United States Food and Drug Administration (FDA) that also targeted cyanuric acid. (4-8)
However, the Kjeldahl method, the traditional standard technique for measuring protein content by indirectly measuring the nitrogen content in food, remains the most ...