DETERMINATION OF PHOSPHORUS IN TURBID WATERS USING ALKALINE POTASSIUMPEROXODISULFATE DIGESTION

The evaluation of the use of alkaline peroxodisulphate digestion with autoclaving or microwave heating for the determination of total phosph orus in turbid lake and river water is described. Procedures were eval uated by the analysis of suspensions (20, 50 and 100 mu g P/l) of two standard reference materials, National Institute of Environmental Scie nce, Japan No. 3 Chlorella and No. 2 Pond Sediment. Suspensions were p repared by adding these materials to distilled deionized water (pH 6) and homogenisation using shaking, sonification and stirring. Best reco veries of phosphorus were found when the final solution was 0.045 M in potassium peroxodisulphate and 0.04 M in sodium hydroxide and solutio ns digested in an autoclave at 120 degrees C for 60 min. or heated in a microwave oven at 450 W for 10 min. Complete recoveries of phosphoru s (99-103%) from 20, 50 and 100 mu g P/l Chlorella suspensions were ob tained using both autoclave and microwave heating. For the Pond Sedime nt complete recoveries of phosphorus (99-107%) from the 20 and 50 mu g P/l suspensions were obtained using both heating methods. Higher reco veries from the 100 mu g P/l Pond Sediment suspensions were obtained u sing microwave heating (96 +/- 1%) than autoclaving (88 +/- 5%). Recov eries of phosphorus compounds (phosphates, and phosphonates) added to distilled deionized water and turbid lake water were near quantitative (91-117%) for both digestion procedures. Further analysis of Pond Sed iment suspensions showed that complete recovery of phosphorus (98 +/- 1%) from 60 mu g/l suspensions was achieved with incomplete recoveries (92.3 +/- 0.7%, 91 +/- 2% and 91 +/- 1%) from 79 mu g P/l, 80 mu g P/ l and 90 mu g P/l suspensions respectively. Comparison with the APHA-A WWA WPCF, nitric-sulphuric acid digestion method showed no difference in phosphorus measurements for the microwave procedure but that the au toclave procedure gave significantly lower recoveries of phosphorus (p < 0.01), however, differences were only 2-8%.