Electrospray positive ionization tandem mass spectrometry of Amadori compoundsThe Maillard reaction, the nonenzymatic interaction between reducing sugars and amino acids, is one of the most important reactions in food and human bodies. 1,2 Amadori compounds are N-substituted 1-amino-1-deoxyketoses, which are formed in the initial phase of the Maillard reaction by Amadori rearrangement, representing a key class of Maillard intermediates. 3,4 The importance of Amadori compounds results from the fact that their formation as well as decomposition can occur under physiological conditions and during food processing and storage. Amadori compounds play a central role in the production of aroma, taste, and color. 5 -9 Furthermore, it has been shown that these compounds are accompanied by a reduction in the nutritive value and the formation of toxic compounds, which have a remarkable effect on the health of human, and so this type of compounds has attracted considerable attention. 10 -13 Many methods have been used to analyze Amadori compounds, such as gas chromatography with sample derivatization prior to analysis, 14 high-performance liquid chromatography, 14 high-performance anion exchange chromatography with an electrochemical detector, 15 and so on. However, the analysis of Amadori compounds was still a challenging task because they are numerous and their structures are similar. With the development of soft ionization technology applied in the field of mass spectrometry over the past decade, fast atom bombardment tandem mass spectrometry 16 and the coupling of tandem mass spectrometry to capillary electrophoresis 17 were successfully used to identify a few glucose-derived Amadori compounds. Recently, electrospray ionization tandem mass spectrometry has become an important means of analysis of organic molecules. High-performance ion exchange chromatography coupled to tandem mass spectrometry 18 has been applied to analyze several Amadori compounds. But the systemized research of mass spectrometry of Amadori compounds and the fragmentation modes of the compounds under electrospray ionization condition have not been developed yet. In this paper, the 18 Amadori compounds were prepared from the reactions between the 18 common amino acids found in food and human bodies with glucose. After purification by high-performance liquid chromatography, the mass spectrometry (ESI-MS/MS) of these compounds was carried out. Moreover, their main fragmentation pathways are summarized.The preparation of Amadori compounds is shown in Scheme 1. Samples of individual Amadori compounds were prepared by refluxing powdered anhydrous glucose (20 mmol), malonic acid (5 mol), and the corresponding amino acid (20 mmol) in methanol (30 ml) under nitrogen for 6 h. After the solutions were cooled to room temperature, the precipitates were removed by filtration (the unreacted glucose and amino acid were filtered off). Each filtrate was concentrated to approximately 15 ml in vacuo. Dropwise addition of anhydrous acetone to the ice-cooled filtrate yiel...