Total phosphorus Lake Bidighinzu

The organic compounds containing nitrogen and phosphorus are simultaneously oxidized to nitrate and orthophosphate with the oxidizing mixture potassium persulfate, boric acid and sodium hydroxide; oxidation is simultaneous thanks to the variation between pH 9.7 and 5 obtained during oxidation by the boric acid - sodium hydroxide system. The total phosphorus is instead determined by the reaction of orthophosphate with ammonium molybdate and potassium antimony tartrate which leads to the formation of a phosphomolybdic antimony complex, in turn reduced by L-ascorbic acid to the molybdenum blue complex which has the maximum absorbance at 882 nm.