Sonnen K18A Kjeldahl Nitrogen Determinator
| Brand | Sonnen |
|---|---|
| Origin | Shanghai, China |
| Manufacturer Type | Authorized Distributor |
| Regional Classification | Domestic (China) |
| Model | K18A |
| Price Range | USD 1,100 – 2,100 |
Overview
The Sonnen K18A Kjeldahl Nitrogen Determinator is a fully integrated, benchtop instrument engineered for accurate and reproducible total nitrogen quantification in organic and inorganic samples via the classical Kjeldahl digestion and distillation method. Based on ISO 8968-1, AOAC 984.13, and ASTM D1122–22 standards, the system automates the three core stages of Kjeldahl analysis: acid digestion (using concentrated H₂SO₄ and catalyst), alkaline distillation, and titrimetric or colorimetric endpoint detection. Designed for routine QC/QA laboratories in food, feed, fertilizer, environmental, and pharmaceutical sectors, the K18A delivers consistent recovery rates (>99.5% for certified reference materials such as BCR-279 and NIST SRM 8414), with measurement linearity across 0.1–200 mg N per sample. Its modular architecture supports both macro- and semi-micro digestion configurations, ensuring adaptability to diverse sample matrices and throughput requirements.
Key Features
- Automated digestion control with programmable temperature ramping (up to 450 °C) and real-time acid reflux monitoring via integrated cooling water flow sensor
- Dual-mode distillation: selectable steam generation rate (0–100% adjustable) with pressure-stabilized steam supply for uniform vapor delivery
- Integrated titration module featuring high-precision burette (±0.01 mL resolution), pH electrode-based endpoint detection, and optional colorimetric mode using bromocresol green/methyl red indicator
- Corrosion-resistant reaction chamber constructed from high-purity quartz and PTFE-lined components to withstand prolonged exposure to hot sulfuric acid and caustic alkali
- Onboard data logging with timestamped run records, including digestion time, distillation duration, titrant volume, and calculated %N — compliant with GLP audit trail requirements
- Front-panel interface with tactile keypad and LCD display; optional RS-232/USB connectivity for LIMS integration and remote parameter configuration
Sample Compatibility & Compliance
The K18A accommodates solid, liquid, and semi-solid samples weighing 0.1–5.0 g (or up to 10 mL for liquids), including dairy products, cereals, meat homogenates, soil extracts, wastewater sludge, and polymer additives. Sample digestion vessels are compatible with standard 250 mL and 400 mL Kjeldahl flasks. The instrument meets essential safety and performance criteria outlined in IEC 61010-1 (Electrical Safety for Laboratory Equipment) and conforms to CE marking requirements. All analytical protocols align with internationally recognized validation frameworks: method precision adheres to ISO 5725-2 repeatability limits; accuracy is verified against CRM-certified materials traceable to NIST and BAM. For regulated environments, the system supports user access levels, electronic signature capability (via optional software upgrade), and full 21 CFR Part 11 compliance when paired with validated PC-based control software.
Software & Data Management
The K18A operates natively via embedded firmware but integrates seamlessly with Sonnen’s optional KJ-Link PC software (Windows 10/11, 64-bit). This application enables method library management, batch scheduling, automated report generation (PDF/CSV/XLSX), and statistical process control (SPC) charting for nitrogen content trends. Audit trails record all user actions—including method edits, calibration events, and result overrides—with immutable timestamps and operator IDs. Raw data files retain full metadata: digestion temperature profile, steam-on/off timing, titration curve derivatives, and blank correction values. Exported datasets comply with FAIR principles (Findable, Accessible, Interoperable, Reusable) and are compatible with third-party laboratory information management systems (LIMS) via HL7 or ASTM E1384 interfaces.
Applications
The K18A serves as a primary nitrogen quantification platform in accredited testing laboratories performing nutritional labeling (per FDA 21 CFR §101.9), feed formulation (AOAC 984.13), wastewater nutrient discharge monitoring (EPA Method 351.2), and quality control of nitrogen-containing pharmaceutical excipients (USP ). It is routinely deployed in R&D settings for protein content estimation (using standard conversion factors: 6.25 for cereals, 6.38 for dairy, 5.70 for wheat gluten), crude protein equivalence calculations, and validation of alternative nitrogen methods (e.g., Dumas combustion). Its robustness and low cost-per-analysis make it especially suited for high-volume contract labs serving agricultural cooperatives and food processors under ISO/IEC 17025 accreditation.
FAQ
What digestion catalysts are compatible with the K18A?
Copper sulfate–selenium or titanium dioxide–copper sulfate mixtures are recommended; mercury-based catalysts are excluded per RoHS Directive 2011/65/EU.
Can the K18A be used for ammonium nitrate analysis without digestion?
Yes — the distillation module supports direct steam distillation of ammonium salts when digestion is bypassed, following ISO 5984 procedures.
Is method validation documentation provided with the instrument?
A comprehensive IQ/OQ protocol package, including installation checklist, operational verification tests, and blank recovery studies, is supplied with each unit.
What maintenance intervals are recommended for long-term reliability?
Daily: rinse condenser and titration tubing; quarterly: calibrate temperature sensors and verify steam pressure stability; annually: replace digestion chamber gaskets and validate titrant concentration.
Does the K18A support dual-wavelength photometric detection?
No — the base configuration uses single-wavelength colorimetry (420 nm); spectrophotometric endpoint detection requires external UV-Vis instrumentation and manual data import.
