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Keywords:

  • Glucose–analysis;
  • Fructose, glucose, sucrose mixture–analysis;
  • Aldose-ketose equilibrium, dilute alkali–glucose transformation to fructose;
  • Hydroxymethylfurfural formation–acid treatment aldose-ketose equilibrium;
  • UV spectrophotometry–analysis

Abstract

The aldose-ketose equilibrium in dilute alkali is utilized to transform a reproducible fraction of glucose to fructose; e.g., 0.20 N NaOH, 40°, 3.5 hr. Acid treatment, e.g., 1.0 N HCI, 80°, 10 hr., of this alkaline equilibrium solution results in the production of spectrophotometrically assayable hydroxymethylfurfural (HMF) (λmax. = 283 mμ) from the fructose produced. Glucose yields negligible HMF under these acid conditions prior to alkaline treatment. These two techniques permit the assay of fructose and glucose in mixtures. After 30 hr. of alkaline treatment under the stated conditions, fructose and glucose do not yield any HMF on acidification. However sucrose is stable under these conditions and on acidification hydrolyzes to fructose which yields a proportional amount of HMF. These facts permit the assay of fructose, glucose, and sucrose in mixtures. This assay is sensitive to concentrations for all three sugars as low as 10−4M.