Overview
ISO 6145-11:2005 - Gas analysis: Preparation of calibration gas mixtures using dynamic volumetric methods - Part 11: Electrochemical generation - specifies a standardized method to prepare calibration gas mixtures by electrochemical generation of a calibration component and introduction into a complementary gas flow. The method covers volume fraction ranges of (0,1 to 250) × 10‑6 and requires a relative expanded uncertainty (k = 2) of the calibration gas content not greater than 5%. The standard is part of the ISO 6145 series on dynamic volumetric methods for calibration gas preparation.
Key topics and technical requirements
- Principle: Quantity of gas generated is proportional to the electrical charge passed through the electrolytic cell (Faraday’s law). The Faraday constant used is 96 485,341.5 C/mol.
- Calculation: Volume fraction ϕ = qA / (qA + qB), where qA is the generated component flow (derived from current, molar volume, z-electron transfer, temperature and a cell-efficiency factor K) and qB is complementary gas flow.
- Electrolytic cell design: Cell construction must ensure efficient transfer of generated gas into the complementary stream; Annexes provide example cell designs and electrical schematics.
- Apparatus & control:
- Voltage supply typically 0.5–1.0 V; current measurement in the 0.5–5.0 mA range (≈1% uncertainty).
- Complementary gas flow measured/controlled (e.g., calibrated thermal mass‑flow controller for 0.2–5.0 l/min, ≈1% uncertainty).
- Decomposition potential is identified by onset of gas evolution and stable current reading.
- Uncertainty evaluation: Key uncertainty sources identified include complementary gas flow, gas generation current, absorption/solubility in electrolyte, moisture, temperature, chemical purity and impurities in complementary gas. Cell efficiency (K) must be known or determined experimentally.
Practical applications
- Rapid on‑demand generation of calibration gas mixtures for:
- Calibration of gas analyzers and detectors, especially for corrosive or unstable components that are unsuitable for high‑pressure cylinders.
- Environmental monitoring, process-control instrument calibration, and quality assurance in gas metrology laboratories.
- Electrochemical generation is suitable for small volume fractions (sub‑ppm to hundreds of ppb) of gases such as O2, H2, HCN, H2S, Cl2, Br2, ClO2, NH3, NO, N2, CO2, PH3, AsH3 and O3 (as noted in the standard).
Who should use this standard
- Calibration laboratories, manufacturers of gas analyzers, instrument metrologists, and organizations needing traceable, low‑concentration calibration gases with controlled uncertainty.
Related standards
- ISO 6145-1 (Methods of calibration)
- ISO 6143 (Comparison methods for checking composition of calibration gas mixtures)
- ISO 6145-7 (Thermal mass‑flow controllers) and other parts of the ISO 6145 series
Keywords: ISO 6145-11:2005, electrochemical generation, calibration gas mixtures, dynamic volumetric methods, gas analysis standard, electrolytic cell design, uncertainty evaluation, complementary gas, Faraday constant.
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