Selective colorimetric/visual detection of Al3+ in ground water using ascorbic acid capped gold nanoparticles

Abstract

A method for the selective and sensitive detection of aluminium (Al3+) in aqueous systems has been developed. The detection is achieved by the selective aggregation of ascorbic acid capped gold nanoparticles (AA-AuNPs) in the presence of aluminium which is observed by the change in colour of the colloidal solution from bright red to purple. The change in characteristic absorption peak can also be noticed spectrophotometrically; absorption of AA-AuNPs (λmax–520nm) decreased and a second peak at 652nm appeared after the addition of aluminium. The ratio of A652/A520 can be used to quantify the concentration of aluminium in water. The method gave a linear response from 20ppb − 100ppb (R2=0.996) of Al3+ in drinking water with a detection limit of 6.5 ppb. The proposed method did not suffer any interference from concomitant transition metal ions like: Mn2+, Ni2+, Zn2+, Sn2+, Li+, Co2+, Hg2+, Fe3+, and Pb2+ up to a concentration of 5ppm and anions (Cl−, F−, SO42−, NO3−, PO43−) up to a concentration of 250ppm. However, a concentration of Ca2+ (≥15ppm) was found to interfere with the detection of Al3+ in ground water. The interference was eliminated by passing the water through an anion exchange resin converted into oxalate form for the removal of the interferant as calcium oxalate precipitate in the resin phase. After this pre-treatment the linearity range in ground water was found to be 100–350ppb with R2=0.996 and LOD − 12.5ppb. The simplicity and rapidity of the developed method shows great potential in favour of its application for screening of drinking water samples to check its safety with respect to aluminium toxicity.