CHNS Elemental Analyzer – Engineering Deep Dive
CHNS analyzers determine elemental composition via complete combustion, gas conversion, chromatographic separation and thermal conductivity detection.
Combustion Chemistry
At ~1000°C in pure oxygen:
- C → CO₂
- H → H₂O
- N → NOx → N₂ (after reduction)
- S → SO₂
A copper reduction column removes excess oxygen and converts NOx to N₂.
Detector Principle (TCD)
Thermal Conductivity Detector measures change in thermal conductivity between reference gas and sample gas.
Signal ∝ concentration of evolved gas.
Calibration Curve
Area = m × Mass + b
Example:
Area = 25000
Calibration slope (m) = 20000
Intercept = 500
Mass = (Area − b) / m Mass = (25000 − 500)/20000 Mass = 1.225 mg
Precision & Uncertainty
%RSD = (Standard Deviation / Mean) × 100
ISO 17025 requires:
- Certified reference material validation
- Blank correction
- Drift correction
- Uncertainty budget documentation
Troubleshooting Flow
- Incomplete combustion → Furnace temperature
- Drift → Gas leak
- Unstable baseline → Detector contamination