NEMI Method Summary

Method Summary Information

Method Number: 365.3 Media: WATER
Revision: Issued 1978
Method Source: U.S. EPA National Exposure Research Laboratory (NERL) [formerly EMSL]
Analytes in this method
Subcategory: INORGANIC
Official Name: Phosphorus, All Forms (Colorimetric, Ascorbic Acid, Two Reagent)
Descriptive Name Phosphorus by Colorimetry
Source Info: U.S.EPA National Exposure Research Laboratory (NERL)
Microbiological and Chemical Exposure Assessment Research Division (MCEARD)
[formerly the Environmental Monitoring Systems Laboratory (EMSL), Cincinnati, OH]
26 West Martin Luther King Drive
Cincinnati, Ohio 45268-0001
Fax: 513-569-7757
email: DWmethods.help@epa.gov
Citation: Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)
17342 Byte file
Brief Method
Summary:
 The sample is pretreated to select the phosphorus forms of interest; the forms are then converted to orthophosphate (which is amenable to the color chemistry of the method). A sample is filtered to select dissolved forms. Polyphosphates are converted to orthophosphate by sulfuric acid hydrolysis. Organic phosphorus is converted to orthophosphate using persulfate digestion.
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 with ascorbic acid to form an intense blue-colored complex. The absorbance of the complex is measured, and is proportional to the orthophosphate concentration.
Scope And
Application:
 This method can determine dissolved and total orthophosphate, hydrolyzable phosphate, and phosphorus (all forms) in drinking, surface and saline waters; domestic and industrial wastes.
Applicable
Conc Range:
 0.01 to 1.2 mg P/L.
Interferences: (A) Arsenate: Arsenate is determined similarly to phosphorus, and should be eliminated by reducing arsenic acid to arseniuos acid with sodium bisulfite.
(B)Iron: Iron can make a low recovery because it will react with the reducing reagent. The bisulfite treatment will eliminate this interference as well.
QC Requirements: None.
Sample Handling: Samples should be collected in plastic or Pyrex glass containers. Samples should be preserved with 2 mL of concentrated sulfuric acid and refrigerated at 4oC. If samples are collected near benthic deposits, take care not to include materials from the deposits.
Max Holding Time:
 48 hours (orthophosphate, dissolved)
28 days (Hydrolyzable and Total)
24 hours (Total Dissolved).
(MCAWW, Table 1).
Sample Prep Met None.
Relative Cost: Less than $50
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