Abstract
Quercetin-sulfonic acid reacts with vanadium(V) to form a stable yellow complex. This complex has a definite absorbance in the pH range from 4.4 to 4.7 when the concentration of quercetin-sulfonic acid in the solution is 3.2×10-4 M. The absorbance is measured at 430 mμ against the reagent blank. Beer's law is obeyed up to 1.0 ppm of vanadium (V). Results of the mole ratio method and of the continuous variation method indicate that 1:1 complex is formed between vanadium(V) and quercetin-sulfonic acid. The molar extinction coefficient is 2.03×104, the sensitivity being 2.6×10-3 μg V per cm2 for the absorbance of 0.001. Zinc, molybdenum, iron, chromium, manganese, magnesium, aluminum, copper and alkali metal salts such as NaF, KBrO3, KIO3 give considerable interference.
