Selective sensing of competitive anions by non-selective hosts: the case of sulfate and phosphate in water

Abstract

Two sensing ensembles based on the common squaramide host 2 and the acid–base indicators Cresol Red (CR) and Bromocresol Green (BG) are described. Both couples were characterized in EtOH–H₂O mixtures by UV-Vis spectroscopy. Analysis of the binding curves and the corresponding Job plots indicate 1 : 1 binding between the indicators CR or BG and host 2. The sensing solutions are responsive to sulfate and/or phosphate anions in water, changing the coloration of the solution. As in other indicator displacement assays (IDA), host 2 translates the chemical event into a colorimetric response that is analyzed by spectrophotometry. However, since other anions present in natural waters do not result in color changes, this method allows the quantification of sulfate and phosphate in water.