ISO 4224:2000 PDF

Overview - ISO 4224:2000 (Ambient air - Carbon monoxide, NDIR method)

ISO 4224:2000 specifies a non-dispersive infrared (NDIR) spectrometric method for the continuous analysis and recording of carbon monoxide (CO) in ambient air. The method covers CO concentrations from 0.6 mg/m3 (0.5 ppm) up to 115 mg/m3 (100 ppm), with a typical lower limit of detection of about 0.06 mg/m3 (0.05 ppm). The standard describes the measurement principle, required apparatus, calibration and sampling procedures, interferences and performance checks.

Key topics and technical requirements

• Measurement principle: NDIR analysis of CO absorption at ~4.7 µm using dual-beam or gas‑filter‑correlation approaches and narrow-band filtering to reduce cross‑sensitivity.
• Applicable range & sensitivity: 0.6–115 mg/m3 operational range; ~0.06 mg/m3 detection limit.
• Interferences and mitigation:
  • Water vapour (primary interferant) - mitigated by drying membranes, constant humidity control, refrigeration, saturating samples, narrow-band filters, or volume corrections.
  • Carbon dioxide and hydrocarbons - typically minimal at ambient levels; CO2 can be scrubbed if required.
• Apparatus & sample conditioning:
  • Complete NDIR analyser (pump, detector, amplifier, recorder).
  • Sample conditioning: flow control, particulate filter, moisture controller.
  • Environmental controls: sampling probe placement (≥1 m from enclosure), enclosure temperature stability (±5 °C), and recording of temperature/pressure.
• Calibration & gases:
  • Multipoint calibration using certified gas cylinders or dynamic dilution of a single standard with zero‑air.
  • Zero‑air (CO