Study On The Determination Techniques For Ultra-trace Orthophosphate In Seawater

Orthophosphate is an essential nutrient element for phytoplankton in ocean environment, and plays an important role in the marine biogeochemical cycle of phosphorus. In oligotrophic open-ocean waters orthophosphate concentrations are down to nanomolar levels. At present, most of the reported determination techniques for orthophosphate have not succeeded in the field of marine environmental science because of their drawbacks as regards sensitivity, reproducibility, chemical interference and ease of use. It is an urgent need to establish sensitive and reliable detection technique for orthophosphate in the oligotrophic open-ocean waters. To meet these requirements, the following studies have been done, and some successful results have been received.(1) A novel method had been set up to determine ultra-trace amount of orthophosphate in seawater with precipitate preconcentration and colorimetric detection. An ion-pair compound of phosphomolybdenum blue (PMB) with cetyltrimethylammonium bromide (CTAB) precipitated from aqueous solution could be easily dissolved in 0.50 mol/L sulfuric acid ethanol solution, and thus determined with a spectrophotometer at 700 nm. Experimental parameters, including the solvent, the reagent concentrations, the time for color developing and precipitation and temperature, were optimized with a univariate experimental design. Under the optimized conditions, using an artificial seawater with salinity of 35 as a matrix, the linearity, the detection limit and the recovery of the proposed method were found to be 0.010 to 0.259μmol/L, 0.003μmol/L and 95.0%, respectively. The relative standard deviation (RSD) ranged from 4.4 to 7.1% for the real seawater samples. Seawater samples were analyzed with both the proposed method and magnesium hydroxide-induced coprecipitation...