Fischer ANalysen Instrumente GmbH

The ¹⁵N emission spectrometer NOI 7

The analyzer NOI 7 is the latest exponent of the successful range of our ^15/14N emission spectrometers.
Hence, the NOI 7 finds its applications within such fields like biology and medicine where problems are pondered relevant to nitrogen. Especially, these are studies on fertiliser efficiency, questions within the field of nitrogen fixation in ecosystems and investigations in the protein metabolism as well as gastroenterological examinations.

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Fields of application

Medicine

• diagnostic studies for Helicobacter-gastritis
• specific liver function tests
• role of amino acids in the parenteral nutrition
• resorption of amino acids and peptides
• intermediary metabolism of N compounds
• modelling of human protein metabolism
• whole body protein turnover
• studies on:
  • kidney function
  • general N metabolism
  • nitrogen retention

Environmental research

• investigation of solids
  • deposition studies
  • emission of nitrogen oxides
  • leaching of nitrogen compounds
• plant research
  • uptake of nitrogen oxides
  • N release by plants
  • N fixation in ecosystems
• exposure research
  • influence of air pollution to children
  • studies on environment/health interactions
• limnology and marine biology
  • nitrate contamination of ground water
  • source identification
  • nitrification and denitrification

Soil science and plant nutrition

• fertiliser efficiency
• biochemistry of N metabolism in plants (biosynthesis, protein quality, amino acid turnover)
• Nitrogen dynamics in soils

Animal nutrition and biochemistry

• protein and nitrogen metabolism
• utilisation of feedstuff
• dynamics of protein synthesis

Special features

The NOI program integrates the intuitive operability of the device and the safe operator guidance in all measuring phases into a cleanly arranged MS-Windows^® application.
Though size reduction and embodiment of all essential components and integration of the computer into the analyzer, the unit providing the comfort of operation expected of modern equipment of this kind.

Operating principle

The emission spectrum of nitrogen shows readily resolvable and comparatively large isotope shifts in the 2-0 band. For measuring, the nitrogen is carried by helium as carrier gas to the basic unit. At a reduced pressure, the nitrogen is excited, using an electric (high frequency) field. In a polychromator, the emitted light, which contains the information about the three possible combinations of the two stable nitrogen isotopes ¹⁴N and ¹⁵N, is dispersed into its spectral components.
A highly sensitive spectroscopy photodiode array, high precision A/D converter and sophisticated digital signal processing ensure that the accuracy of the measured data is comparable with that of some mass spectrometers; the advantage here is that the shortcomings of a mass spectrometer – e.g. higher cost, susceptibility to faults and more complicated operation – are non-existent.

System configuration

The NOI 7 consists of the basic unit accommodating the high-frequency excitation components, detector, data acquiring and evaluating computer and a unit for generating the sample gas. Available are the Chemical Sample Conversion System NOI 7C and various types of elementary analyzers.

Measuring sealed discharge tubes

The discharge tubes are prepared by means of an external conversion apparatus. The NOI 7 measurements are extremely simple and take only a few seconds. Only the basic unit is needed.

Measuring liquid samples

Using the NOI 7C system, the relative ¹⁵N abundance in the aqueous solution containing the key substance NH₄Cl, which is obtained in most cases by Kjeldahl digestion, can be determined directly as an atomic percentage.
Within the NOI 7C the molecular nitrogen is released from the ammonium-containing sample solution by addition of an aqueous sodium hypobromite solution:

2NH₄ + 3BrO + 2OH → N₂ + 5H₂O + 3Br

and carried by a continuous helium stream to the basic unit. High-precision components ensure the constant helium stream and pressure needed in this process. Optionally, an automatic sampler matching with the NOI 7C can be installed. This sampler permits the measurements to be carried out automatically.

Measuring solid samples

The installation of a DUMAS combustion unit (which is incorporated in an elementary analyzer) upstream of the unit has the advantage of a direct conversion of liquid or solid samples and permits the total nitrogen to be determined.