Determination of serum-phosphate without deproteinization by ultraviolet spectrophotometry of the phosphomolybdic acid complex.

Phosphate may be determined in serum without deproteinization as the phosphomolybdic acid complex by UV-spectrophotometry. The rate of complex formation is dependent on the acidity and the concentration of molybdate. The photometric measurements should be performed at a longer wavelength than in maximum absorptivity of the phosphomolybdic acid complex to permit practical high concentrations of molybdate in the reagents. Citric acid will hinder the complex formation, but will not interfere with the stability of the phosphomolydbic acid. The phosphomolybdic complex is determined by adding citric acid to the samples before (blank) and after (test) the molybdate. The analytical procedure has been automated on a Greiner GSA II, Greiner Electronics, Switzerland.