Analytical application of the reaction of hafnium(IV) with ο-hydroxyhydroquinonephthalein in the presence of fluoride ion and cetylpyridinium chloride

Abstract

A rapid and simple spectrophotometric method for the determination of Hf (IV) and F- with ο-hydroxyhydroquinonephthalein (Qn.Ph.) in the presence of cetylpyridinium chloride (CPC) and fluoride ion has been proposed. Hafnium(IV) reacted with Qn. Ph. in the presence of the excess CPC as a cationic surfactant and F-, to form a colored complex which was soluble in water. The decrease in the absorbance of the Qn.Ph. solution and the increase in that of the Qn. Ph.-Hf (IV)-F- solution were observed in the presence of CPC. The absorption maximum of the Qn.Ph.-Hf (IV)-F- solution was about 555 nm against the reagent blank, and its absorbance was constant in the pH range of 4.5 to 6.3 in the presence of 2.0×10-3 M CPC. The calibration curves were linear in the concentration range of 017.5 μg/10 ml for Hf (IV) and (1.04.0) μg/10 ml for F-, respectively. The Sandell sensitivities of this method were 0.0017 μg/cm2 for Hf(IV) and 0.0013 μg/cm2 for F-, respectively. The apparent molar absorptivity at 555 nm was 1.2×105 l mol-1 cm-1 for Hf (IV). The molar ratios of Hf(IV) to Qn.Ph. were found to be 1 : 2 in the presence of F- and 1 : 1.5 in the absence of F-, respectively.