This method is a persulfate oxidation technique for nitrogen and phosphorus where, under alkaline conditions, nitrate is the sole N product and phosphate is the sole P product. A platinum catalyst greatly enhances this procedure. The direct measurement of particulate C, N and P is the preferred method used in this laboratory. The greater volume filtered onto the pad yields a concentrated, representative sample. The alternative, subtraction of the dissolved from the total sample via persulfate digestion to determine the particulate concentration, sometimes yields negative values when the dissolved fraction is proportionately large.
Direct measurement is rapid, more sensitive and more precise.
This is EPA Method 440.0. This analysis does not distinguish between particulate organic and particulate inorganic components of a sample. It has been determined that the carbon and nitrogen particulate component is almost entirely organic in natural waters of such areas as Chesapeake Bay, Long Island Sound and New York Bight. This is a total analysis where both inorganic and organic components are included. It has been determined that for Chesapeake Bay waters there is a varied and sometimes substantial inorganic particulate P component both temporally and spatially.