Abstract
Cathechol-4-sulfonate(PCS) reacted with aluminum to form water-soluble stable complexes, with molar ratio of Al to PCS 1:1 in pH range from 4.5 to 6.0, 1:2 in pH from 6.5 to 8.5 and 1:3 in pH greater than 9.0. The stability constants of these complexes determined by potentiometric titration were logK1=16.5, logK2=12.8 and logK3=8.19, and the acid dissociation constants of hydrogen complexes were pKHAIO(OH)Pc+=3.24, pKHAl(O2Pc)O(OH)Pc2-=4.94 and pKHAl(O2Pc)2O(OH)Pc5-=7.53 in 0.1N KNO3 solution at 25.00.1°C.
For the determination of aluminum was employed 1:2 complex, Al(O2Pc)23-. It showed two absorption peaks at 255 mμ and 298 mμ. The maximum absorbance at 298 mμ was obtained in the pH range from 7.0 to 8.5. The molar absorptivity of the 1:2 complex was 1.25×104 at 298 mμ, and the sensitivity of determination at pH 7 was 0.0023 μg Al/cm2. Beer's law was strictly followed at least up to 1 μmol/25 ml. The reaction of Al3+ ion with PCS was fast and the equilibrium was attained within 40 seconds at room temperature. The color intensity did not change for more than 10 hours.
The results indicated that PCS was useful as a reagent for the classification of the hydrolysis products of aluminum salt into mononuclear and polynuclear species by difference in their rate of formation of the colored complex and also for their spectrophotometric determination.
