Colorimetric sensing of H2PO4− using a Pb2+ complex of a pyridylazo dye in aqueous solution

Abstract This study develops a sensitive and selective colorimetric probe for the detection of dihydrogen phosphate (H 2 PO 4 − ) based on a lead ion (Pb 2+ ) complex of a commercially available pyridylazo dye (PAPS) in aqueous media under physiological conditions. The complex was made by adding Pb 2+ to PAPS in a 1:1 stoichiometric ratio (PAPS‐Pb 2+ ), which was accompanied by the remarkable solution change from yellow to purple. The colorimetric sensing of H 2 PO 4 − over other anions with PAPS‐Pb 2+ occurred owing to the regeneration of original PAPS by the interaction of H 2 PO 4 − with Pb 2+ in a 1:2 molar ratio. Moreover, the H 2 PO 4 − detection was less affected by the presence of other coexisting competitive anions. The colorimetric naked‐eye behaviour of PAPS‐Pb 2+ rendered a useful and convenient probe for the detection of H 2 PO 4 − via the indicator displacement assay.