Colorimetric method for the determination of ketoses using phenol-acetone-boric acid reagent (PABR)

A purplish pink color developed when ketose solution (100 microliters) was mixed with phenol-acetone-boric acid reagent (0.5 ml 5% phenol, 2% acetone, 4% boric acid) and then treated with 96% sulfuric acid (1.4 ml). The absorbance of the reaction mixture was measured at 568 nm after 60 min at 37 degrees C. This method allowed the simple determination of 3-50 nmol of D-fructose with coefficient of variation 7.8% for 3 nmol and 2.8% for 50 nmol. Carbohydrates other then ketoses did not interfere with this reaction. The influence of various chemicals on the colorimetric reaction and applicability of the method for determination of ketoses in natural products are presented.