Determination of inorganic phosphorus in the presence of organic phosphorus and high concentrations of proteins

Abstract

The phosphorus assay method of Lowry and Lopez has been modified to permit a rapid and accurate determination of inorganic phosphorus in the presence of organic phosphorus without prior deproteinization of the samples. The reduction of ammonium phosphomolybdate to molybdenum blue is carried out with ascorbic acid in the presence of acetate buffer, pH 4.0, containing 10% sodium dodecyl sulfate to prevent protein precipitation. The method is applicable to samples containing up to 30 mg protein per milliter of final reaction volume. Acid-labile phosphorus compounds present in serum are not hydrolyzed, and less than 5% phosphocreatine is split during the time necessary for the assay. The addition of SDS to the buffer does not affect the sensitivity and reliability of Lowry and Lopez's method.