Rapid, sensitive and selective spectrophotometric determination of phosphate as an ion associate of 12-molybdophosphate with Astra Phloxine

A highly sensitive and selective reaction of 12-molybdophosphate with the polymethine dye Astra Phloxine has been used for the spectrophotometric determination of phosphate. If the concentration of phosphate is less than 1 µmol L−1, supersaturated solutions of ion associate (IA) are stable without the use of a surfactant. Under these conditions, a new band appears in the absorption spectrum at 574 nm. The color of the IA develops immediately after mixing of reagents and remains constant over several hours. The molar absorptivity of the IA is 1.54 × 105 L mol−1 cm−1. The calibration graph is linear between 0.02 and 0.8 µmol L−1 of phosphate. The limit of detection is 7 nmol L−1. Phosphate was determined in pure chemicals and water samples, including Dead Sea water.