Studies on the spectrophotometric determination of phosphorus using hydriodic acid as a reducing agent, and a proposed new method applicable to serum and urine

Abstract

1. 1. The determination of phosphorus as molybdenum blue using HI as the reducing agent of phosphomolybdic acid has been investigated. 2. 2. The reaction is found to be dependent on temperature and also on the concentrations of molybdate, potassium iodide, and acid employed. Optimal conditions for each of these variables have been evaluated and described. 3. 3. The use of HI as reductant results in a 2 1 2 fold increase in sensitivity when compared with amino-naphthol-sulphonic acid. In addition, very stable colours are produced which conform to Beer's law. 4. 4. A method of estimation of serum and urine phosphorus which take advantage of these features is presented which requires 0.5 ml serum to perform. This volume may be still further reduced if necessary. 5. 5. The described method was found to be highly reproducible, and recoveries of P added to serum fell between 97–104%. The range of serum phosphorus concentration in 52 healthy adults was found to be 3.3 mg% ± S.D. 0.51 mg%.