Selective ionization of melamine in powdered milk by using argon direct analysis in real time (DART) mass spectrometry

Abstract

5-Hydroxymethylfurfural (5-HMF) is a compound with the elemental composition C₆H₆O₃ that is present in powdered milk. Protonated 5-HMF (calculated m/z 127.0395) has the same nominal m/z as protonated melamine (calculated m/z 127.0732) and can interfere with direct analysis of melamine in powdered milk. Tandem mass spectrometry and high-resolution mass spectrometry have been previously used to distinguish melamine from 5-HMF. An alternative approach is presented here that uses the direct analysis in real time (DART™) ion source operated with argon gas in combination with acetylacetone and pyridine reagent gases to selectively ionize melamine and eliminate the interference from 5-HMF. High-resolution/accurate mass data were used to verify the elimination of the 5-HMF interference and confirm the melamine elemental composition. With further refinement, this technique could lead to a rapid analysis method for screening large numbers of samples.