Design of an Optical Sensor for Aluminium(III) Determination Based on Immobilization of Eriochrome Cyanine R on a Triacetylcellulose

A selective optical sensor based on immobilization of Eriochrome Cyanine R for the determination of Al(III) ions in aqueous solution has been developed. The method is based on the spectrophotometric measurement of complex Eriochrome Cyanine R-aluminium at 537 nm. The sensing membrane is made of a triacetylcellulose film containing Eriochrome Cyanine R colorimetric reagent immobilized as an ion pair with methyltrioctylammonium chloride. The response of the sensor is based on the Eriochrome Cyanine R absorbance decrease by the coordination of Al(III) ions. At pH= 6.0, the linear dynamic rangeis varied from 3.22×10-8 to 4.10×10-5 mol L-1 with a detection limit of 1.2× 10-8 mol L-1. A dynamic working range, detection limit, sensitivity, selectivity and the response time were discussed in detail. The response was pH dependent. The membrane responds to Al(III) ions irreversibly by changing color from pink to blue. The membrane was regenerated in less than 30 seconds with 0.1 mol L-1 EDTA solution and was ready for further measurements. The response time of the sensor was within 16 min depending on the concentration of Al (III) ions. The sensor response was found to have a repeatability and reproducibility of 1.62% and 3%, respectively. The sensor provides appropriate selectivity to Al(III) ions over transition metal cations, including Co(II), Ni(II), Fe(III), Cu(II) and Zn(II). The sensor has been used for the determination of Al(III) ions in potable water and aluminium – magnesium syrup.