Fluorimetric method for the determination of low concentrations of dissolved aluminium in natural waters

Abstract

Dissolved aluminium occurs in natural waters down to concentrations of 1 µg l^–1 or less. There are very few methods that are sufficiently sensitive to measure down to these levels. A fluorimetric method using the reagent Lumogallion has been investigated and found to have a detection limit of 0.05 µg l^–1 of aluminium and a coefficient of variation of 5% at the 1.0 µg l^–1 level and 2.7% at the 22 µg l^–1 level. The only anionic interference likely to be important in most natural waters is that from fluoride, and this interference can be dealt with by using an incremental calibration procedure. For acidic waters iron is a potential interferent but has no significant effect at concentrations of less than 100 µg l^–1. In water abnormally rich in dissolved organic material there may be competition for the dissolved aluminium between the natural organic ligands and the Lumogallion. This effect can be overcome by ultraviolet irradiation prior to analysis for aluminium. The analysis detects all forms of aluminium in filtered natural water samples except when the aluminium occurs in stable mineral structures, e.g., clay particles small enough to pass through the filter. Aluminium adsorbed on the surface of such particulate material appears to be determined.