What is Kjeldahl analysis?
The Kjeldahl method is the reference wet-chemistry procedure for determining organic nitrogen — and, via a conversion factor, crude protein — in food, feed, dairy, soil, fertilizer and water samples.
Three steps, fully automated.
Digestion
The sample is digested in concentrated sulphuric acid with a catalyst on a digestion block (Smart, X, S or Gr series), converting organic nitrogen to ammonium.
Distillation
Alkali is added and steam distillation releases the ammonia, which is absorbed in boric acid — automated on every K-series analyzer.
Titration
The absorbed ammonia is titrated to a colorimetric end point detected by a 16-bit tri-primary color sensor (built in on K06, K12, K18 and K1306; external on K1305/K1301).
Data handling
Results are calculated, stored and exported — K12/K18 store up to 5,000,000 test results with USB, Wi-Fi and host-control output; K18 adds LIMS connectivity.
Semi-automatic vs fully automatic.
The defining difference is the titration system. A semi-automatic analyzer (K1301) automates reagent addition, distillation and waste handling, while the end-point titration happens off-line. A fully automatic analyzer (K06, K12, K18, K1306) adds the titration system in-line, so the result comes out directly without manual operation during the determination. All K-series models share the 0.1–240 mg N measuring range and a listed 3–8 minutes per sample.
Sonnen’s K12 and K18 additionally provide an auto-sampler interface — the A20 AutoSampler is the current recommended solution for unattended batches.
Instruments for the method.
Standards built on Kjeldahl.
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