Naked Eye Chemosensor for the Qualitative and Quantitative Determination of Oxalate Ions Based on Indicator Displacement Assay

Herein, a simple, sensitive, and rapid chemosensor is reported for the colorimetric detection and determination of oxalate ions. This system produces a visible color change from purple to yellow based on the indicator displacement assay (IDA) approach. The reaction of Eriochrome Cyanine R (ECR) as an indicator and vanadyl ions (VO2+) at pH 6.00 acts as a chemosensor for oxalate ions (Ox). Adding oxalate ions to the designed chemosensor causes the replacement of the vanadyl ions with the oxalate ions to binding the indicator. Due to this displacement, the solution color returns to yellow with about 80 nm blue shifts (530 to 450 nm). Also, the formation constants of ECRVO2+ and VO2+-Ox complexes were determined to be 6.13 and 13.94, respectively using spectrophotometric titration. Under the optimized experimental conditions, the chemosensor exhibited a dynamic linear range for oxalate ions from 8.30 × 10-7 -1.13 ×10-4 M, with a detection limit (S/N = 3) of 5.40 × 10-7 M. The relative standard deviation (RSD) value was evaluated to be 0.52% for five determinations of oxalate (6.02 μM). The designed sensor was applied successfully for the determination of oxalate ions in human urine samples with the recoveries of 96.36 to 105.73% showing satisfactory results.