Nutrient Analytical Services Laboratory

Water Column Chemistry


Orthophosphate


Ammonium molybdate and antimony potassium tartrate react in an acid medium with dilute solutions of phosphorus to form an antimony-phospho-molybdate complex which is reduced to an intensely blue-colored complex by ascorbic acid. Color is proportional to phosphorus concentration.

Technicon Industrial Method No. 155-71W/Tentative. 1973. Technicon Industrial Systems. Tarrytown, New York, 10591.

USEPA. 1979. Method No. 365.1 in Methods for chemical analysis of water and wastes. United States Environmental Protection Agency, Office of Research and Development. Cincinnati, Ohio. Report No. EPA-600/4-79-020 March 1979. 460pp.

Froelich, P.N. and M.E.Q. Pilson. 1978. Systematic absorbance error with Technicon AutoAnalyzer II colorimeter. Water Res. 12:599-603.



Ammonium


Determination of ammonium is by the Berthelot Reaction in which a blue-colored compound similar to indophenol forms when a solution of ammonium salt is added to sodium phenoxide, followed by the addition of sodium hypochlorite. The addition of a potassium sodium tartrate and sodium citrate solution prevents precipitation of hydroxides of calcium and magnesium.

Technicon Industrial Method No. 804-86T. August 1986. Technicon Industrial Systems. Tarrytown, New York, 10591.

Kerouel, R. and A. Aminot. 1987. Procédure optimisée hors-contaminations pour l'analyze des éléments nutritifs dissous dans l'eau de mer. Mar. Environ. Res. 22:19-32.



Nitrite


Nitrite reacts under acidic conditions with sulfanilamide to form a diazo compound that couples with N-1-naphthylethylenediamine dihydrochloride to form a reddish-purple azo dye measured at 520 nm..

Technicon Industrial Method No. 818-87T. February 1987. Technicon Industrial Systems. Tarrytown, New York, 10591.




Nitrite + Nitrate


Filtered samples are passed through a granulated copper-cadmium column to reduce nitrate to nitrite. The nitrite (originally present plus reduced nitrate) then is determined by diazotizing with sulfanilamide and coupling with N-1- naphthylethylenediamine dihydrochloride to from a colored azo dye. Nitrate concentration is obtained by subtracting the corresponding nitrite value from the nitrite + nitrate concentration.

Technicon Industrial Method No. 158-71 W/A† Tentative. 1977. Technical Industrial Systems. Tarrytown, New York, 10591.

USEPA. 1979. Method No. 365.2 in Methods for chemical analysis of water and wastes. United States Environmental Protection Agency, Office of Research and Development. Cincinnati, Ohio. Report No. EPA-600/4-79-020 March 1979. 460pp.




Silicate


This reaction is based on the reduction of silicomolybdate in acidic solution to “molybdenum blue” by ascorbic acid. Oxalic acid is added to minimize interference from phosphates.

Technicon Industrial Method No. 811-86T. November 1986. Technicon Industrial Systems. Tarrytown, New York, 10591.




Total Dissolved Nitrogen and Phosphorus


This method is a persulfate oxidation technique for nitrogen and phosphorus where, under initially alkaline conditions, nitrate is the sole nitrogen product. Phosphate is the sole phosphorus product after acidic conditions are achieved following further autodecompositon of the persulfate in the heated oxidation tubes. Digested samples are passed through a granulated copper-cadmium column to reduce nitrate to nitrite. The nitrite then is determined by diazotizing with sulfanilamide and coupling with N-1- naphthylethylenediamine dihydrochloride to form a colored azo dye. Color is proportional to nitrogen concentration. Ammonium molybdate and antimony potassium tartrate react in an acid medium with dilute solutions of phosphorus to form an antimony-phospho-molybdate complex which is reduced to an intensely blue-colored complex by ascorbic acid. Color is proportional to phosphorus concentration.

D'Elia, C.F., P.A. Steudler, and N. Corwin. 1977. Determination of total nitrogen in aqueous samples using persulfate digestion. Limnol. Oceanogr. 22: 760-764.

Valderrama, J.C. 1981. The simultaneous analysis of total nitrogen and total phosphorus in natural waters. Mar. Chem. 10: 109-122.



Total and Dissolved Organic and Inorganic Carbon


The Shimadzu TOC-L uses a high temperature combustion method to analyze aqueous samples for TOC and non-purgeable organic carbon (NPOC). Samples are treated with sulfuric acid to reduce the pH, and sparged with ultra-pure carrier grade air to drive off inorganic carbon. High temperature combustion (680 °C) on a catalyst bed of platinum-coated alumina balls breaks down organic carbon into carbon dioxide (CO2). The CO2 is carried by ultra-pure air to a non-dispersive infrared detector (NDIR) where CO2 is detected. The method used is EPA 415.1.

The Shimadzu TOC-5000A is used to determine Total Inorganic Carbon (TIC), and carbonate alkalinity is calculated from the TIC concentration. Samples are injected into 25% v/v Phosphoric Acid (H3PO4), and the released CO2 is carried by ultra-pure air to a non-dispersive infrared detector (NDIR) where CO2 is detected. The method is described in the instrument manual for the TOC-5000A.



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