Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion

A flow injection system for the automatic determination of total phosphorus in beer is described. The developed manifold uses a two-stage photooxidati on/thermal digestion procedure together with oxidizing and hydrolyzing reag ents to convert all forms of phosphorus compounds to orthophosphate. Polyph osphates are hydrolyzed by acid and heat, and organo-phosphates are digeste d by UV-catalyzed peroxodisulfate oxidation. The orthophosphate formed is t hen spectrophotometrically determined by the phosphomolybdenum blue reactio n, using stannous chloride as reducing agent. The results obtained for a se t of 19 beer samples (with concentrations from 120 to 735 mg P/L) were in g ood agreement with the reference method, the maximum relative deviation fou nd being 4.7%. Relative standard deviations for ten consecutive determinati ons were lower than 1.5%, and a detection limit of 1 mg P/L was achieved.