Separation and partial characterization of Maillard reaction products by capillary zone electrophoresis

Capillary zone electrophoresis proved useful for separating small amounts of both charged and uncharged solutes that are otherwise difficult to analyse. A typical complex mixture that had previously resisted all analytical approaches, including reversed-phase separations, is the products arising from the reaction of free amino acids with aldehydic sugars (Maillard reaction products). By using capillary zone electrophoresis [untreated capillary 50 cm x 75 microns I.D., 18 kV, 0.02 mol/l phosphate buffer (pH 7.5)], a number of products resulting from the reaction of glucose or ribose with glycine, alanine and isoleucine were separated and partially characterized. They were separated (1) without derivatization (and profiles of compounds absorbing at 220 nm were obtained), (2) as phenylthiocarbamyl derivatives in a search for reactive amino groups and (3) after derivatzation with 2,4-dinitrophenylhydrazine in a search for a method for compounds with a free aldehydic group. Phenylthiocarbamyl derivatives were separated in 0.005 mol/l borate buffer (pH 9.6) at 20 kV and 25 microA. Separation of 2,4-dinitrophenylhydrazones was effected by electrokinetic micellar chromatography in the same apparatus using a 50 cm x 75 microns I.D. capillary at 10 kV in 0.01 mol/l Na2HPO4-0.006 mol/l tetraborate, 0.050 mol/l with respect to sodium dodecyl sulphate. The results are compared with those given by high-performance liquid and thin-layer chromatography.