USGS-NWQL: I-2545: Nitrogen, nitrite plus nitrate, dissolved, colorimetric, ASF
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Official Method Name
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Nitrogen, nitrite plus nitrate, colorimetry, cadmium reduction-diazotization, automated-segmented flow |
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Current Revision
| 1973 |
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Media
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WATER |
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Instrumentation
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Automated Spectrophotometer |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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M.J. Fishman, 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--Determination of inorganic and organic constituents in water and fluvial sediments: U.S. Geological Survey Open-File Report 93-125 |
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Brief Method Summary
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An acidified sodium chloride extraction procedure is used to extract nitrate and nitrite from samples of bottom material for this determination (Jackson, 1958). Nitrate is reduced to nitrite by cadmium metal. Imidazole is used to buffer the analytical stream. The sample stream then is treated with sulfanilamide to yield a diazo compound, which couples with N-1naphthylethylenediamine dihydrochloride to form an azo dye, the absorbance of which is measured colorimetrically. The result is the sum of the nitrite originally present plus that formed by the reduction of the nitrate (Morris and Riley, 1963; Brewer and Riley, 1965; Wood and others, 1967; Strickland and Parsons, 1972; Nydahl, 1976; Sherwood and Johnson, 1981; Patton, 1982; U.S. Environmental Protection Agency, 1983). |
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Scope and Application
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This method is used to analyze samples of surface, domestic, and industrial water and brines containing from 0.05 to 5.0 mg/L of nitrite- plus nitrate-nitrogen. Samples containing greater concentrations must be diluted. Originally started in 1973, this modified method was implemented in the National Water Quality Laboratory in March 1988. |
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Applicable Concentration Range
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0.05 to 5.0 mg/L |
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Interferences
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Concentrations of potentially interfering substances generally are negligible in unpolluted surface and ground water. For specific details of inorganic and organic compounds that interfere, see Norwitz and Keliher (1985, 1986) as well as more general information from the American Society for Testing and Materials (1991). Sulfides, often present in anoxic water, rapidly deactivate cadmium reactors by forming an insoluble layer of cadmium sulfide on the active metal surface (Strickland and Parsons, 1972). The buffer capacity of the imidazole solution and the approximate 10:1 volume ratio of buffer to sample eliminate the possibility of erroneous results for moderately acidic (pH > 1) samples. Mercury (II) does not interfere. It rapidly forms an amalgam on the inlet end of the cadmium reactor without detriment to the reduction reaction. |
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Quality Control Requirements
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Calibrate instrument using calibration standards (CAL); quality control samples (QCS); and laboratory blanks (LB) analyzed at a minimum of 1 for every 10 samples. |
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Sample Handling
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Container Description: 125 mL brown polyethylene bottle. Treatment and Handling: Filter through 0.45 micron filter; use filtered sample to rinse container; preservation with mercuric chloride; chilled to 4 degrees C and ship immediately. |
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Maximum Holding Time
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30 days |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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