Catalytic spectrophotometric methods for the determination of oxalic acid

A new catalytic kinetic spectrophotometric method for the determination of oxalic acid has been described, based on its catalytic effect on the redox reaction between dichromate and rhodamine B, measured at the maximum absorption wavelength of 555 nm in sulphuric acid. Under the optimum conditions of 0.05 mol l−1 H2SO40.003 mol l−1 K2Cr2O73.28 × 10−6 mol l−1 rhodamine B at 90°C for 8 min, a calibration graph from 0.06 to 4 μg ml−1 oxalic acid and a detection limit of 20 ng ml−1 was obtained. No serious interferences were identified. Oxalic acid in spinach leaves and waste water was determined by this method, with satisfactory results.