Labconco Open Combination (Macro) Kjeldahl Systems 2123Series User Manual
Page 21
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Titrimetric Determination
Various scientific associations offer approved Kjeldahl methods. These
methods are available at their websites. The AOAC International (
Official
Methods of Analysis
), Association of American Cereal Chemists (
Approved
Methods
), American Oil Chemists Society, Environmental Protection Agency
(
EPA Methods for Chemical Analysis of Water and Wastes),
International Standards
Organization, The National Forage Testing Association, and United States
Department of Agriculture.
This methodology is for reference only. It is not a citable document. It is
based on data we believe to be reliable. It is offered in good faith but without
guarantee.
1. Scope and Application
1.1. This method determines the Total Kjeldahl Nitrogen (TKN) in water,
and organic substances. There are three steps within the method: 1.
the digestion procedure – which converts organic nitrogen to
ammonia, 2. the distillation procedure - transferring ammonia from
the digested sample to an ammonia trapping solution 3. Sample
titration – the quantification of ammonia in the trapping solution.
NOTE 1:
Some compounds containing nitrogen may not be converted;
such as amines, nitro-compounds, hydrazones, oximes,
semicarbazones and some tertiary amines.
1.2. This method is described for use with Kjeldahl equipment using
Macro-Size glassware (500 - 800 ml flasks).
2. Definitions
2.1. TKN is defined as the sum of free-ammonia and organic nitrogen
compounds, converted to ammonium sulfate (NH
4
)
2
SO
4
by acid
digestion.
3. Apparatus
3.1. Digestion Apparatus: A Kjeldahl digestion apparatus with multiple
600 watt electric burners, using 500 - 800 ml flasks and a fume
removal manifold system.
3.2. Distillation Apparatus: A Kjeldahl distillation apparatus with
multiple 600 watt electric burners, using 500 - 800 ml flasks. The
distillation system includes connecting bulbs to prevent mechanical
carryover of NaOH during distillation, water cooled condensers and