A new dipstick colorimetric sensor for detection of arsenate in drinking water

Abstract

The present work reports on a polymer hydrogel-based cost effective colorimetric dipstick sensor for arsenic(V). The method was based on the formation of a blue colored antimonyl–arseno–molybdate complex in the presence of ammonium molybdate, potassium antimonyl tartrate and ascorbic acid. All these reagents were encapsulated in a polymer hydrogel made of polyvinyl alcohol, acrylamide and glutaraldehyde. Plastic detector strips were dip coated with this hydrogel. Scanning electron microscopy (SEM) depicted the highly porous structure of the polymer hydrogel permitting adsorption of As(V) confirmed by energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) analysis. The advantages were low sample volume (10 ml), low detection limit (10 μg L⁻¹ by the naked eye), good stability (4 months), low cost (0.03$ per test for visual detection), and high reproducibility. The sensor strips displayed selectivity in the presence of <100 μg L⁻¹ of phosphate (arsenate structural analog) and 3 mg L⁻¹ of iron. Changes in the RGB (red, green, and blue) values of color spots on the As(V) colorimetric dipstick sensor with various concentrations of As(V) created a pattern. The dominance of B (blue) values was revealed in low concentration range of As(V) while the R (red) values dominated in higher concentrations. The same strip could be used for detection of total arsenic in case the sample contained As(III). Phosphate interference could also be detected by a simple modification of the procedure. When applied to real groundwater arsenic contaminated samples, the results were in good agreement with the atomic absorption spectrophotometry (AAS) results as visualized by statistical analysis.