Separation and Purification of Glucose in Sake for Carbon Stable Isotope Analysis

An existing procedure for the separation and purification of glucose in sake for compound-specific carbon stable isotope analysis was examined with a view to reducing the sample amount required and process complexity, with a focus on the freeze-drying, solid-phase extraction (SPE), and high-performance liquid chromatography (HPLC) steps. In the revised procedure, the carbon stable isotopic composition, as indicated by delta C-13 values, of glucose was not significantly affected by glucose concentration in the range 0.25-1.00 mg mL(-1), solvent (water or 80% aqueous acetonitrile), or HPLC procedure. Glucose freeze-dried after separation and purification by SPE and HPLC exhibited procedure-induced carbon isotopic discrimination of <= 0.1 parts per thousand. The isolation procedure achieved the same accuracy in glucose delta C-13 values as that achieved with traditional ion-exchange procedures while requiring a sample volume (1 mL) only 4% that of the usual volume. The improved method enables cost-effective, labor-efficient, small-scale, compound-specific carbon stable isotope analyses of glucose in sake.