Simultaneous digestion for determination of total phosphorus and total nitrogen in sea water

This paper described the condition of digestion of the total phosphorus and total nitrogen in the sea water simultaneously with potassium persulfate-boric acid-sodium hydrate as the digestive reagents.The result showed that the digestive reagent concentration was K_(2)S_(2)O_(8) 7.5 g/L,H_(3)BO_(3) 4.5 g/L,NaOH 2.1 g/L,add 10 mL of the reagents to 10 mL sample,autoclaved for 30 min at(125±1)℃,then the total phosphorus and total nitrogen transformed to available phosphate and nitrate simultaneously.The total nitrogen was determined by ultraviolet spectrophotometer,and the absorbency needed to be emendated by ΔA=A_(220 nm)-2A_(275 nm).The total phosphorus with sulfuric acid-ammonium stibium molybdate-ascorbic acid as the developer was determined by spectrophotometer at 700-720nm wave length.This method is suitable to both sea water and fresh water.The total phosphorus linear range of calibration curve in fresh water and sea water are 0-4.0(mg/L),and the detection limit is 0.017 mg/L.The total nitrogen linear range of calibration curve in fresh water is 0-4.0 mg/L,while 0-8.0 mg/L is in sea water.The detection limit is 0.029 mg/L.The recovery rates of total nitrogen and total phosphorus was 95.4%-114%, and 93.7%-108%,respectively.