Indirect Amperometric Detection of Aluminium by Flow Injection Analysis Using DASA as Ligand

Abstract

The analytical technique for aluminium was based upon the complexation reaction between aluminium (Al) and a ligand 1,2‐dihydroxy‐anthraquinone‐3‐sulfonic acid (DASA). The system consists of a commercial electrochemical analyzer, flow injection components (manifold, pumps, and valves), and an in‐house designed control system to perform automated analysis. Good linearity was observed for Al standards within a range (0 to 1.6 mg/L) that was applicable to water treatment analysis. Interfering ions, including Fe2+, Fe3+, Ca2+, Mg2+, Cu2+, and Zn2+, were studied, but only Fe interfered with the Al analysis. Iron, Fe, interference was removed by utilizing two masking agents (o‐phenanthroline and 2,2′‐bipyridyl) to prevent any Fe interaction with DASA. The hydrodynamics of the manifold (suitable mixing of reagents) was examined by the inclusion of different reactor types, including the super serpentine reactor™ (SSR™) that produces a high degree of mixing with minimal axial dispersion. The amperometric detector applied to this system was a BAS UniJet cell that maximizes the current response for the oxidation of DASA. In conjunction with the total aluminium concentration measured by techniques such as ICP‐AES, this system is capable of providing aluminium speciation information in water, particularly for drinking water by the determination of DASA reactive labile Al. By combining these sources of information, we can observe the changes in the labile/total Al ratio for three drinking waters (0.46, 0.15, and 1.09) that cover the range of Al residual from raw water to an underdosed and an optimally dosed water, respectively. This ratio informs the plant operator about the nature of Al species in water in addition to the quantities present. The authors would like to thank John Bannigan for his assistance with the construction of some of the in‐house hardware used here. The financial assistance from the CRC for Water Quality and Treatment to fund the work of Shaun Thomas is acknowledged and was greatly appreciated.