Colorimetric detection of phosphate-based on iron complexing catechol-displacement assay in eutrophicated water bodies

A simple, sensitive, and inexpensive colorimetric indicator-displacement assay based on Fe³⁺-catechol complex has been developed to determine PO₄^3-. The Fe³⁺ and catechol formed a greenish color complex, upon the addition of PO₄^3- to the complex, it exhibited a visual color change immediately from greenish to colorless along with UV–vis spectral change. This change was mainly attributed to the high binding affinity of PO₄^3- with Fe³⁺ by displacing catechol from the Fe³⁺-catechol complex. The developed sensor showed good sensitivity for the determination of PO₄^3- in a wide linear range from 2 − 1000 µM with a limit of detection (LOD) of 0.5 µM which was found to be lower than the permissible limit. The sensor presented good selectivity towards the detection of PO₄^3- in the existence of other potential interfering anions. Furthermore, the method was successfully applied to determine PO₄^3- in eutrophicated water bodies (river and lake water) with good recoveries and without showing any significant matrix effect.