EPA Method 349

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EPA Method 349:
Ammonia in Estuarine and Coastal Waters by Colorimetry. Official Name: Determination of Ammonia in Estuarine in Coastal Waters by Gas Segmented Continuous Flow Colorimetric Analysis

This method is based on the indophenol reaction and employs an automated gas-segmented continuous flow analysis system. A sample is introduced into the system, and ammonia in the sample reacts with alkaline phenol and NaDTT upon heating (and in the presence of a catalyst) to form indophenol blue. The concentration of ammonia in the sample is determined by measuring indophenol blue with a spectrophotometer; correcting for errors due to matrix through data processing.

This method determines total ammonia (NH3 and NH4+) in estuarine and coastal waters.

Methods for Determination of Chemical Substances in Marine and Estuarine Matrices - 2nd Edition (EPA/600/R-97/072)

Interferences (A) Hydrogen sulfide: Hydrogen sulfide > 2 mg/L should be removed by acidifying the sample and stripping with nitrogen.(B) Metals: Complex calcium and magnesium using sodium citrate or EDTA to prevent precipitation of calcium and magnesium hydroxides in alkaline reagent solution.(C) Turbidity: Remove turbidity using filtration.(D) Refractive index: Error due to difference in the refractive index of saline and reagent waters are corrected using salinity matching.

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.

Maximum Holding Time:
3 hours; 14 days for preserved estuarine and coastal water samples with moderate to high concentrations of ammonia



The method is linear up to 4 mg-N/L.

Precision and accuracy values were calculated using data from seven replicate analyses of a fortified sample matrix having a salinity to 35.5% and a background ammonia concentration of 6.3 ug-N/L. The method contains additional data on method performance.

The MDL was determined in 3 analyte-fortified seawater matrices of different salinities according to the MDL procedure at 40 CFR part 136, Appendix B. The procedure also is detailed in Section 9.2.2 of the method.

Revision Number:
Revision 1.0, September 1997