ONLINE PHOTOOXIDATIVE DECOMPOSITION OF PHOSPHORUS-COMPOUNDS TO ORTHOPHOSPHATE AND ITS APPLICATION TO FLOW-INJECTION SPECTROPHOTOMETRIC DETERMINATIONS OF TOTAL PHOSPHORUS IN RIVER AND WASTE-WATERS

A simple and mild on-line photo-oxidative decomposition method for the highly sensitive flow-injection spectrophotometric determination of t otal phosphorus in river and waste waters was developed for the first time by using low pressure mercury lamps. Organic and inorganic phosph orus compounds in sample solutions were injected into a carrier soluti on, which merged with the decomposition solution containing sulfuric a cid and potassium peroxodisulfate. The solution components were decomp osed oxidatively to orthophosphate while flowing in a photo-reactor. A fter the decomposition, orthophosphate was determined spectrophotometr ically based on the formation of Molybdenum Blue. The photo-reactor co nsisted of two low pressure mercury lamps, a poly(terafluoroethylene) (PTFE) tubing and a reflection mirror. The PTFE tubing was wound direc tly around the mercury lamps, which were covered with reflection mirro r. The detection limit for phosphorus was about 0.001 mg l(-1), and th e sample throuphput was about 20 samples per hour for total phosphorus determination. By using the photo-reactor, most of the phosphorus com pounds were decomposed completely, whereas some condensed phosphates w ere less susceptible to photo-oxidation. The analytical results for pr actical samples obtained by the proposed method showed a good correlat ion with those obtained by using a heat-oxidation method, which indica tes that the content of the condensed phosphates difficult to be decom posed was very scarce in the practical samples.