Catalytic Kinetic Spectrophotometric Method for Determination of Phosphate Ion

The kinetic method for the determination of phosphate microamounts was described. The developed method is based on catalytic effect of phosphate on sodium pyrogallol-5-sulphonate (PS) by dissolved oxygen. The reaction was followed spectrophotometrically by measuring the rate of change in the values of the absorbance of the oxidation product at 437 nm. The optimum reaction conditions are PS (0.44×10⁻³ mol·L⁻¹) and HClO₄ (3.6×10⁻⁶ mol·L⁻¹) at 25 °C. Following this procedure, phosphate can be determined with a linear calibration graph up to 0.23 µg·mL⁻¹. The interference effect of several species was also investigated and it was found that the most common cations and anions did not interfere with the determination. The developed procedure was successfully applied to the determination of phosphate in natural waters and soil.