Spectrophotometric study of the iron(III)-morin complex in a micellar medium

Abstract

A spectrophotometric study of the iron(III)-morin complex in the presence of several surfactants (non-ionic, cationic and anionic) at different concentrations is reported. The study was performed at pH 4, and all the surfactants used (except a non-ionic surfactant of the ethylene oxide-propylene oxide condensate group) solubilised the complex. However, maximum sensitisation could be obtained only by using non-ionic surfactants.

A subsequent spectrophotometric study in the presence of the non-ionic surfactant Nemol K-1030 (polyoxyethylenated nonylphenol) was carried out. The green-brown complex formed in micellar medium showed maximum absorption at 417 nm. Using a concentration of 8.95 × 10^–6M of Fe(III), the optimum conditions were 1.18 × 10^–4M(0.004%) morin, 1.25 × 10^–2M(1%) Nemol K-1030 and pH 3.7, adjusted with acetic acid-acetate buffer. No variations in absorbance were observed between 15 and 35 °C.

The stoicheiometry of the Fe(III)-morin complex in the presence of 1% of Nemol K-1030 was calculated by the molar ratio, continuous variations and slope ratio methods. A ratio of Fe(III) to morin of 1 : 4 was found in all instances. The mean conditional formation constant was found to be 3.90 × 10²².

Using a morin concentration of 0.004%, the calibration graph was linear up to 1.4 p.p.m. of Fe(III), the molar absorptivity of the complex being 6.33 × 10⁴ l mol^–1 cm^–1. The detection and quantification limits were found to be 0.0038 and 0.012 p.p.m. of Fe(III), respectively. A study in the presence of different ions showed that the most important interferences are due to Zr(IV), Al(III), Ti(IV), and V(IV) and V(V).