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Water for Kjeldahl Analysis

 
 
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Impact of Water


Water is used in many steps of the Kjeldahl analysis. It is used in the preparation and dilution of the reagents, standards and samples, and for rinsing the glassware and the apparatus. Water may also be used after the digestion step, and to generate steam for the distillation step of the analysis. It may also be used for cooling (in condensers, etc.).

The following water contaminants may interfere with the analysis and should be avoided:
  • Ammonia and nitrogen-containing molecules
    Molecules containing nitrogen (organic and inorganic) may interfere with the analysis, and lead to erroneously high results. For instance, nitrates, can disturb the nitrogen mass balances. All nitrogen-containing compounds should be kept to a minimum. 
  • Ions and metals
    Calcium and magnesium salts, as well as metals (iron, copper and manganese) may generate deposits when the water is heated to produce steam. These deposits may restrict water flow and reduce the heat exchange efficacy of the steam generator. More frequent maintenance will also be needed. 
  • Particles
    Particles may form deposits in the vessels or when steam is generated. Removing these deposits may be cumbersome. 
  • Bacteria
    Bacteria levels should be kept to a minimum, as they may form biofilms in the steam generator, and lead to additional need or maintenance. In addition, bacteria release by-products, including nitrate, nitrite and other nitrogen-containing compounds, that may interfere with the analysis. 
Freshly purified ultrapure water is recommended for Kjeldahl analysis. Some instruments, originally designed to perform Kjeldahl analysis, offer the option to perform related analyses, such as Total Kjeldahl Nitrogen (TKN) or Devarda analysis, or to analyze volatile components, such as Total Volatile Basic Nitrogen (TVB-N). It is important to follow instrument manufacturer’s guidelines regarding the water quality to use. Ultrapure water is usually recommended for these analyses.


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