Total Kjeldahl Nitrogen

This method is used for the determination of Total Kjeldahl Nitrogen in drinking, surface and saline waters, domestic and industrial wastes, plants and soils. The EPA range of this method is 0.1 to 20 mg/L as nitrogen. However, this method is also applicable to other ranges.

Summary

Ammonia reacts with salicylate and hypochlorite in a buffered alkaline solution in the presence of sodium nitroferricyanide (pH 12.8-13) to form the salicylic acid analog of indophenol blue. The blue-green color produced is measured at 660 nm.

Limitations

Precipitation of calcium and magnesium hydroxides is eliminated by potassium sodium tartrate in the working buffer. Samples that are turbid must be filtered or centrifuged prior to determination. Samples with background absorbance at the analytical wavelength may interfere.

Availability

System Method # Range(s)
Flow System A071

0.05 – 2 mg/l as N
0.1 - 10 mg/L
0.2 - 80 mg/L
0.4 – 20 mg/L
2.0 - 200 mg/L

Astoria 2 A071 0.05 – 2 mg/l as N
0.1 - 10 mg/L
0.2 - 80 mg/L
0.4 – 20 mg/L
2.0 - 200 mg/L
rAPID-T N/A  0.1 - 10 mg/l as N