Fluorimetric determination of aluminium with morin after extraction with isobutyl methyl ketone. Part I. Fluorescence of the aluminium-morin complex in an isobutyl methyl ketone-ethanol-water system

Abstract

A method for the fluorimetric determination of aluminium with morin (3,5,7,2′,4′-pentahydroxyflavone) in an isobutyl methyl ketone (IBMK)-ethanol-water system is proposed, with a 3-to 4-fold increase in sensitivity over the conventional method. The optimum conditions were found to be as follows: 40% of IBMK, 20% of an aqueous solution containing the aluminium and HCl-KCl to adjust the pH and 40% of methanol-ethanol-water (86 + 9 + 5) solution, which is necessary for the dispersion of the IBMK in water, and in which the reagent, morin, is dissolved. The optimum pH is 3.7–3.8 (HCl-KCl buffer) and the fluorescence is measured after 1 h at 495 nm, with excitation at 418 nm, at 25 °C.

Using a morin concentration of 0.005%, the calibration graph is linear for concentrations up to 40 p.p.b., and the limit of detection of the method is 0.2 p.p.b. A study of 17 interfering ions showed that the most important interferences are due to Be²⁺, Zn²⁺, Pb²⁺, Fe³⁺, Fe³⁺, Cu²⁺ and F^–, and in most instances it was found that the tolerance limits are higher than with the conventional method for the determination of aluminium with morin.