Simplified Serum Phosphorus Analyses by Continuous-Flow Ultraviolet Spectrophotometry

Serum phosphorus can be measured by continuous-flow uv spectrophotometry without reduction of the phosphomolybdate complex. The dilute sample is dialyzed into dilute (1 ml/100 ml) sulfuric acid, then mixed with an ammonium molybdate— sulfuric acid—"Tween 80" solution. The absorbance of the sample peaks is measured at 340 nm with a linear-absorbance spectrophotometer. Peak heights are directly proportional to concentration, because logarithmic conversion is performed within the spectrophotometer. The method obeys Beer’s law up to 10 mg of P per deciliter, and results correlate closely with those for standard methods based on reduced phosphomolybdate blue. The miniature manifold uses a 12-in. dialyzer. The sampling rate can be 60 to 120 samples per hour when a Gilford one-piece debubbler flow cell is used.