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United States Department of Agriculture

Agricultural Research Service

Title: Analyzing for Total P and Total Dissolved P in Water Samples

Authors
item Pote, Daniel
item Daniel, Tommy - UNIV OF ARKANSAS

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: March 14, 2000
Publication Date: June 1, 2000
Citation: POTE, D.H., DANIEL, T.C.2000. ANALYZING FOR TOTAL P AND TOTAL DISSOLVED P IN WATER SAMPLES. BOOK CHAPTER. IN METHODS OF PHOSPHORUS ANALYSIS FOR SOILS, SEDIMENTS, RESIDUALS, AND WATERS. 396:94-97.

Technical Abstract: The phosphorus form most available to aquatic plants is dissolved orthophosphate, but numerous studies have shown that other forms of P can be hydrolyzed to orthophosphate in waste water treatment facilities and in natural waters. Therefore, when assessing the long-term potential for accelerated eutrophication of surface water due to P loading, many researchers and watershed managers want to know the total P concentration (regardless of P form) in water samples. However, polyphosphates, organically-bound phosphates, and particulate P do not react with the molybdate reagent used for colorimetric P analysis, so these P fractions must first be converted (hydrolyzed) to orthophosphate before they can be determined colorimetrically. Thus, analysis for total P content requires digestion of the water samples to oxidize the organic matter and release all P as orthophosphate. Published methods have been available for many decades, and some improvements have been made, but the digestion process always requires heat and/or various strong acids, sometimes in combination with strong oxidizing agents, a procedure that can be time- consuming and dangerous. Complete descriptions and discussion (including calculations) of several preferred digestion methods are included in this chapter. To determine the total dissolved P fraction, particulate P is removed by filtering the water sample through a membrane (0.45-micron pore diameter) before beginning the digestion procedure.

Last Modified: 11/22/2014
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