NEMI Method Summary

Method Summary Information

Method Number: 365.5 Media: WATER
Revision: Revision 1.4, September 1997
Method Source: U.S. EPA National Exposure Research Laboratory (NERL) [formerly EMSL]
Analytes in this method
Subcategory: INORGANIC
Official Name: Determination of Orthophosphate in Estuarine and Coastal Waters by Automated Colorimetric Analysis
Descriptive Name Orthophosphate in Estuarine and Coastal Waters 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 Determination of Chemical Substances in Marine and Estuarine Matrices - 2nd Edition (EPA/600/R-97/072)
76674 Byte file
Brief Method
Summary:
 This method is based on the method of Murphy and Riley. A sample is introduced into an automated segmented flow analyzer. Orthophosphate reacts with ammonium molybdate and ammonium potassium tartrate in an acidic medium to form an antimony-phoso-molybdate complex. The complex is reduced using ascorbic acid, and the concentration of orthophosphate is determined by measuring the absorbance of the reduced complex with an on-line colorimeter.
Scope And
Application:
 This method determines low-level orthophosphate concentrations in estuarine and coastal waters.
Applicable
Conc Range:
 The method is linear up to 0.39 mg-P/L
Interferences:

(A) Hydrogen sulfide: Dilute samples with high sulfide contents to minimize interferences.

(B) Turbidity: Remove turbidity using filtration.

(C) Metals: High iron concentrations can precipitate phosphate.
QC Requirements: Initial demonstration of performance, continued analysis of Laboratory Reagent Blanks (LRB), laboratory duplicates, and Laboratory Fortified Blanks (LFB) with each set of samples as a continuing check on performance.
Sample Handling: Samples collected using hydrocast or submersible pump systems. Turbid samples must be filtered through a 0.45 um membrane or glass fiber filter immediately after collection. Samples to be analyzed within 24 hours should be stored at 4oC until analysis. If samples cannot be analyzed within 24 hours, then freezing at -20oC for a maximum period of two months is acceptable.
Max Holding Time:
 24 hours; two months if stored at -20oC
 
Relative Cost: Less than $50
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