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Simplified Method for the Determination of Total Kjeldahl Nitrogen in Water and Wastewater
Oral Presentation
Prepared by C. Jackson
Hach Company, 5600 Lindbergh Drive, Loveland, Colorado, 80539
Contact Information: cjackson@hach.com; 970-669-3050
ABSTRACT
Total Kjeldahl Nitrogen (TKN) is defined as the sum of organic nitrogen and ammonia present in a wastewater sample. A preliminary digestion is used to oxidize carbon compounds to carbon dioxide, and convert organic forms of any nitrogen present (amino acids, proteins, peptides) to ammonia. The traditional digestion uses sulfuric acid in combination with mercury or copper catalysts and salts. Maco-digestion (500 mL) of at least two hours is followed by addition of sodium hydroxide, where the ammonia is distilled into boric acid or buffer solution. The ammonia distillate is then measured by back titration or nesslerization.
In the simplified TKN method (s-TKN™), inorganic and organic nitrogen (total nitrogen) are oxidized to nitrate by micro-digestion with peroxodisulfate. The micro-digestion (<2 mL) takes one hour and requires no distillation. The nitrate ion from the distillate is reacted with 2,6-Dimethylphenol in a solution of sulfuric acid and phosphoric acid to form nitrophenol where it is measured colorimetrically. A second sample is analyzed for nitrate-nitrite by reacting with 2,6-Dimethylphenol, measured colorimetrically, then subtracted from the results of the digested sample. sTKN results are comparable to traditional macro digestion and analysis methods. This talk compares and contrasts the tow TKN methods, both in performance, cost of analysis, and green chemistry implications.
Oral Presentation
Prepared by C. Jackson
Hach Company, 5600 Lindbergh Drive, Loveland, Colorado, 80539
Contact Information: cjackson@hach.com; 970-669-3050
ABSTRACT
Total Kjeldahl Nitrogen (TKN) is defined as the sum of organic nitrogen and ammonia present in a wastewater sample. A preliminary digestion is used to oxidize carbon compounds to carbon dioxide, and convert organic forms of any nitrogen present (amino acids, proteins, peptides) to ammonia. The traditional digestion uses sulfuric acid in combination with mercury or copper catalysts and salts. Maco-digestion (500 mL) of at least two hours is followed by addition of sodium hydroxide, where the ammonia is distilled into boric acid or buffer solution. The ammonia distillate is then measured by back titration or nesslerization.
In the simplified TKN method (s-TKN™), inorganic and organic nitrogen (total nitrogen) are oxidized to nitrate by micro-digestion with peroxodisulfate. The micro-digestion (<2 mL) takes one hour and requires no distillation. The nitrate ion from the distillate is reacted with 2,6-Dimethylphenol in a solution of sulfuric acid and phosphoric acid to form nitrophenol where it is measured colorimetrically. A second sample is analyzed for nitrate-nitrite by reacting with 2,6-Dimethylphenol, measured colorimetrically, then subtracted from the results of the digested sample. sTKN results are comparable to traditional macro digestion and analysis methods. This talk compares and contrasts the tow TKN methods, both in performance, cost of analysis, and green chemistry implications.