Spectrophotometric Determination of Iron(III) with 8-Quinolinol in the Presence of Sodium Dodecyl Sulfate Micelle

Abstract

It has been known that iron (III) reacts with 8-quinolinol to form a water insoluble complex. However, in the presence of sodium dodecyl sulfate (SDS) which is a most typical anionic surfactant, the precipitate of the complex is made water soluble above a critical micelle concentration (CMC) of SDS, while it is not made below the CMC. This phenomenon may be ascribed to the dissolution of the complex into the micelle of SDS, which is called the solubilization. The solubilized complex is stable for at least 2-3 days and has two absorption maxima at 460 and 580 nm. Absorbances keep nearly constant values over a high concentration region above the CMC of SDS.
This describes the spectro photometric method for the determination of iron (III) based on the coloration of the iron (III) 8-quinolinol complex solubilized in the SDS micelle. Recommended procedure is as follows: Take sample solution containing up to 500μg of iron (III). Add 5 ml of 0.6% 8-quinolinol solution, 1 ml of 0.625 mol/l SDS solution and 10 ml of distilled water. Adjust the pH to 5.0 with NH₄OH solution and CH₃COONH₄ solution and make up the final volume to 50 ml with distilled water. Measure the absorbances at 460 and 580 nm against a blank. Beer's law holds for 1-10 ppm of iron 010. The apparent molar extinction coefficients at 460 and 580 nm are 4.7 X 10³ and 3.6 x 10³, respectively.The sensitivities at 460 and 580 nm are 0.011 and 0.015 pg Fe (III)/cm² for log (I₀/I) = 0.001 level, respectively.
The interference of copper ( II ) can be eliminated by addin g KCN solution as a masking agent, and that of vanadium ( V ) by measuring the absorbance at 580 nm after the solution is finally made alkali.