Analysis of phosphate in serum with the phosphate redox electrode system

A phosphate redox electrode system (PRES) was designed, constructed, and evaluated for analysis of inorganic phosphate in serum. This system is based on the observed phosphate ion potential of a chemically treated iron wire in a turbulent flow-through cell at constant oxygen tension. We analyzed 110 clinical samples by this technique and with the Technicon SMAC. Of the specimens analyzed, 32% contained abnormal phosphate concentrations. Each was assayed two to four times with the PRES and once with the SMAC. The PRES assay rate was 60 samples/h. Mean phosphorus concentrations (and SEM) were: PRES, range of values for replicate data sets, 30.5-31.0 (0.5-1.1) mg/L; SMAC, 30.8 (1.0) mg/L. Results for the PRES (y) correlated well with those by the SMAC: r = 0.968 to 0.980, estimated slope = 0.99 to 1.03, and estimated intercept = -1.1 to 0.1 mg/L. Differences in results by the two methods were not statistically significant.