Improved diffusion methods for nitrogen and 15nitrogen analysis of Kjeldahl digests

Area of Science:

• Analytical Chemistry
• Environmental Science
• Agricultural Science

Background:

• The Kjeldahl method is a standard for determining nitrogen content.
• Efficient ammonia (NH3) collection is crucial for accurate nitrogen (N) analysis.
• Existing methods may have limitations in reliability, capacity, or convenience.

Purpose of the Study:

• To describe simple, reliable methods for collecting ammonia (NH3) from Kjeldahl digests.
• To improve the analytical capacity and convenience of ammonia (NH3) collection.
• To validate these methods for both quantitative and isotope-ratio analyses of nitrogen (N).

Main Methods:

• Utilized boric acid (H3BO3) indicator solution or acidified filter disks for ammonia (NH3) collection.
• Developed a semimicro digestion procedure with specific sample and reagent volumes.
• Employed diffusion in Mason jars at ambient or elevated temperatures (45-50°C) for ammonia (NH3) trapping.

Main Results:

• Achieved quantitative recovery of diffused nitrogen (N) using both collection methods.
• Isotope-ratio analyses of diffused nitrogen (N) from diverse samples (chemical, plant, soil) showed high accuracy.
• Results were within 3% of those obtained by traditional steam distillation methods.

Conclusions:

• The described methods offer a reliable and convenient approach for ammonia (NH3) collection in Kjeldahl analysis.
• These techniques are suitable for both total nitrogen (N) quantification and stable isotope analysis.
• The improved methods provide accurate nitrogen (N) determination comparable to steam distillation.