Fluorimetric determination of aluminium with morin after extraction with isobutyl methyl ketone. Part II. Extraction-fluorimetric determination of aluminium in natural and waste waters

Abstract

A fluorimetric study of the extraction of the Al-morin complex into isobutyl methyl ketone (IBMK) was carried out. At pH 5–7 an extraction efficiency of between 90 and 100% was obtained, being a maximum (100%) at pH 6 when the Al content was 10 p.p.b. and 97% at 20 p.p.b.

A 1-ml volume of 0.125% morin solution was added to 50 ml of Al solution adjusted to pH 6 ± 0.5; 10 ml of IBMK were introduced and the mixture was shaken for 5 min, then allowed to settle for 10 min. The organic phase was separated and dispersed with 10 ml of ethanol-methanol-water (86 + 9 + 5); the pH was adjusted to 3.7–3.8 and the solution was diluted with water to 25 ml. The fluorescence intensity was measured after 1 h at 495 nm with excitation at 418 nm, and the results were compared with those obtained with standards of aluminium that did not require extraction.

The fluorescence intensity was linear up to 20 p.p.b. of Al and the limit of detection was 0.1 p.p.b. From a study of interferences it was deduced that, after the extraction, the F^– and PO₄^3– interferences were eliminated, and the selectivity towards SiO₃^2–, Be, Cu, Mg and NH₄+ was also increased.

The proposed method was applied to the determination of Al in natural and waste waters, and the results are compared with those obtained by atomic-absorption spectrophotometry by chelation with quinolin-8-ol into IBMK using a heated graphite atomiser and a dinitrogen oxide-acetylene flame.