2nd EPA TKN - METHOD #: 351.1 TITLE: Approved for NPDES,...

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METHOD #: 351.1 Approved for NPDES, CWA (Ed. Rev. 1974, 1978) TITLE: Nitrogen, Kjeldahl, Total (Colorimetric, Automated Phenate) ANALYTE: CAS # N Nitrogen 7727-37-9 INSTRUMENTATION : Autoanalyzer STORET No. 00625 1.0 Scope and Application 1.1 This automated method may be used to determine Kjeldahl nitrogen in surface and saline waters. The applicable range is 0.05 to 2.0 mg N/L. Approximately 20 samples per hour can be analyzed. 2.0 Summary of Method 2.1 The sample is automatically digested with a sulfuric acid solution containing potassium sulfate and mercuric sulfate as a catalyst to convert organic nitrogen to ammonium sulfate. The solution is then automatically neutralized with sodium hydroxide solution and treated with alkaline phenol reagent and sodium hypochlorite reagent. This treatment forms a blue color designated as indophenol. Sodium nitroprusside, which increases the intensity of the color, is added to obtain necessary sensitivity for measurement of low level nitrogen. 3.0 Definitions 3.1 Total Kjeldahl nitrogen is defined as the sum of free-ammonia and of organic nitrogen compounds which are converted to (NH ) SO under the conditions of 42 4 digestion which are specified below. 3.2 Organic Kjeldahl nitrogen is defined as the difference obtained by subtracting the free- ammonia value from the total Kjeldahl nitrogen value. Also, organic Kjeldahl nitrogen may be determined directly byremoval of ammonia before digestion. 4.0 Sample Handling and Preservation 4.1 Samples may be preserved by addition of 2 mL of conc. H SO per liter and 24 refrigeration at 4°C. Even when preserved in this manner, conversion of organic nitrogen to ammonia may occur. Therefore, samples should be analyzed as soon as possible. 5.0 Interferences 5.1 Iron and chromium ions tend to catalyze while copper ions tend to inhibit the indophenol color reaction.
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6.0 Apparatus 6.1 Technicon AutoAnalyzer consisting of: 6.1.1 Sampler II, equipped with continuous mixer.
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This note was uploaded on 03/06/2011 for the course ENV 6666 taught by Professor Fuss during the Spring '11 term at Uni San Francisco de Quito.

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2nd EPA TKN - METHOD #: 351.1 TITLE: Approved for NPDES,...

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