Distinction and quantitation of sugar isomers in ternary mixtures using the kinetic method

Quantitative isomeric analysis of fructose, galactose, and glucose was achieved using electrospray ionization and trimeric ion dissociation with data analysis by the kinetic method. Several L-amino acids and divalent metal cations were tested to select the best systems for isomeric distinction and quantitation of each monosaccharide. High discrimination could be achieved for most tested systems, and serine/Cu(2+) and aspartic acid/Mn(2+) were selected for quantitative analysis due to their ability to strongly distinguish the three analytes and to allow long-term reproducible measuring conditions. Accurate quantitative results were obtained for all isomers using three-point corrected calibration curves, which account for the competition effects evidenced to occur between sugars for the formation of the trimeric complexes. As a result, the relative proportion of one isomer in the liquid and in the gas phase depends on the sugar mixture composition. However, for a given reference/metal system, the extent of competition effects was shown to be constant within a given pair of sugars. The correction factors could thus be established based on data obtained from binary mixtures and successfully used for ternary sample analysis.