Kjeldahl nitrogen & protein analyzers.
In short: Sonnen builds six Kjeldahl nitrogen analyzer lines: semi-automatic distillation units (K1305, K1301) and fully automatic distillation–titration systems (K06, K1306, K12, K18). Recovery is ≥99.5% in standard test mode, and the K18 reaches ≥99.8%. K12 and K18 connect to the A20/A35 autosamplers for unattended 20/35-sample batch operation.
Automated distillation and distillation–titration systems built on the classic Kjeldahl method, with color-sensor end-point detection, ≥99.5% standard recovery (≥99.8% on the K18) and dedicated modules for nitric nitrogen and high-nitrogen samples. The K06, K1306, K12 and K18 run a complete single-sample test cycle unattended once started; the K12 and K18 add an autosampler interface for continuous 20/35-sample batch operation with the A20/A35.
The principle.
Every automatic Kjeldahl analyzer on this page runs the classical three-step Kjeldahl method: the sample is digested in concentrated sulfuric acid (upstream, on a block digester), the released ammonia is steam-distilled into boric acid, and the distillate is titrated to its end point. On fully automatic models the titration — with color-sensor or potentiometric end-point detection, matched to the method and configuration — is integrated in-line, so a started sample completes with no operator in between; on the K12/K18, the same test information is tracked, auditable and exportable to LIMS.
Where it is used
Feed and pet-food protein (AOAC 2001.11), meat and meat products (ISO 937 / AOAC 981.10), cereals and pulses (ISO 20483), milk and dairy (ISO 8968), food and agricultural products (ISO 1871), soil and fertilizer total nitrogen (GB/T 22923 — co-drafted by Sonnen), and water-quality Kjeldahl nitrogen (ISO 5663).
Models in this family
Specifications at a glance.
| Model | Automation level | Measuring range | Recovery (standard test mode) | Time per sample | Autosampler |
|---|---|---|---|---|---|
| K1301 | Semi-automated distillation | 0.1–240 mg N | ≥99% | 5–7 min | — |
| K1305 | Automated distillation | 0.1–240 mg N | ≥99.5% | 5–7 min | — |
| K06 | Fully automatic | 0.1–240 mg N | ≥99.5% | 3–8 min | — |
| K1306 | Fully automatic | 0.1–240 mg N | ≥99.5% | 3–8 min | — |
| K12 | Fully automatic | 0.1–240 mg N | ≥99.5% | 3–7 min | A20 / A35 |
| K18 | Fully automatic, LIMS-ready | 0.1–240 mg N | ≥99.8% | 3–7 min | A20 / A35 |
The K18 reaches ≥99.8% recovery with repeatability RSD ≤0.2%. Digestion is performed upstream on a block digester.
How to choose.
- Single-sample unattended testing — the K06, K1306, K12 and K18 complete a full test cycle without an operator once started.
- Unattended batch operation — K12/K18 pair with the A20 (20-position) or A35 (35-position) autosampler for continuous multi-sample runs.
- High-nitrogen or nitric-nitrogen samples — dedicated modules on the K12/K18; the K18 verifies recovery ≥99.8%.
- Data integrity & LIMS — the K18 adds five-level user management, audit trails and LIMS connectivity for regulated labs.
- Distillation only — K1305/K1301 where titration is handled separately.
Three questions to the right model: 30-second Kjeldahl selector →
Related: The Kjeldahl method — pillar note · ISO 20483 (cereals & pulses) · ISO 8968 (milk & dairy) · Kjeldahl nitrogen analyzer buying guide
Frequently asked questions.
Which Sonnen analyzers support unattended batch testing?
The K12 and K18. Both have an autosampler interface and pair with the A20 (20-position rack-type) or A35 (35-position carousel) autosampler for continuous batch operation. The K06, K1306, K12 and K18 all run a complete single-sample test cycle unattended once started.
What recovery rate do Sonnen Kjeldahl analyzers achieve?
≥99.5% recovery in standard test mode across the K-series; the K18 reaches ≥99.8%, with repeatability RSD ≤0.2%.
Semi-automatic or fully automatic — what is the difference?
The K1305/K1301 automate distillation; the K06, K1306, K12 and K18 automate the complete distillation–titration cycle and calculate the result. Fully automatic models remove the separate titration step and the operator attention it requires.
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An application engineer replies within 24 hours with a model recommendation and quotation.