Spectrophotometric determination of malonate with diazotised 4-nitroaniline

Abstract

When malonate is treated with diazotised 4-nitroaniline for 3 h at 25 °C in acetate buffer solution (pH 5.2) and then with 5 N hydrochloric acid, an intense and stable orange dye is produced with a large absorbance maximum at about 445 nm. Malonate can be determined in this way in the range from about 5 to 50 µg (0.05–0.5 µmol ml^–1). Oxaloacetate, acetoacetate and ascorbate, which produce a similar colour under the same conditions and thus hamper the determination of malonate, are removed by prior immersion of the sample in boiling water and by the addition of sodium nitrite.