ISO 6145-10:2002

Overview

ISO 6145-10:2002 - "Gas analysis - Preparation of calibration gas mixtures using dynamic volumetric methods - Part 10: Permeation method" specifies a dynamic permeation technique for preparing low-level calibration gas mixtures. The standard covers preparation of component mole fractions in the range 10−9 to 10−6, achieving a relative expanded uncertainty of ~2.5%. It defines apparatus, permeation tubes and membranes, procedures for mass-loss determination (periodic or continuous weighing), and operational controls (temperature, flow, purity) needed to generate stable, trace-level calibration gases (e.g., SO2, NO2, benzene).

Key Topics and Requirements

• Principle: Calibration component permeates through a polymer membrane into a controlled carrier gas flow; composition derived from permeation rate and carrier flow.
• Mole fraction range: Designed for ultra-trace concentrations from 10−9 to 10−6.
• Uncertainty: Target relative expanded uncertainty of 2.5% for component mole fraction.
• Apparatus modes:
  • Periodic-weighing (tube removed and weighed periodically)
  • Continuous-weighing (tube suspended on microbalance)
• Materials: Permeation membranes from PTFE, polyethylene, polypropylene, FEP; permeation tubes of glass or stainless steel.
• Temperature control: Critical - permeation rate highly temperature-dependent; control typically within 0.1 K; allow ~72 h to reach/recover equilibrium after changes.
• Flow control and measurement: Use mass flow controllers/meters; two-stage dilution recommended to adjust concentrations without disturbing thermal equilibrium.
• Quality checks: Carrier gas purity verified by GC or FTIR; assess permeation tube purity and discard tubes if permeation rate changes >10%.
• Weighing environment: Controlled temperature and humidity during mass-loss measurements; minimize time tube is outside the temperature-controlled enclosure.

Applications and Who Uses It

• Environmental and air-quality laboratories preparing trace-level calibration standards for continuous emissions monitoring (CEMS) and ambient air networks.
• Reference and national metrology institutes establishing primary or secondary calibration standards.
• Manufacturers of gas analysers and calibrators validating instrument linearity and low-end detection limits.
• Occupational hygiene and petrochemical labs requiring accurate low-level standards for toxic gases and VOCs.
• Use cases include generating calibration mixtures for SO2, NO2, benzene, ammonia and other low-concentration analytes where cylinder stability is inadequate.

Related Standards

• ISO 6145-1: Methods of calibration (general)
• Other parts of ISO 6145 series (e.g., volumetric pumps, thermal mass-flow controllers, saturation and capillary methods)
• Relevant analytical methods: GC, FTIR for carrier gas purity assessment

Keywords: ISO 6145-10, permeation method, calibration gas mixtures, permeation tubes, dynamic volumetric methods, trace gas calibration, permeation membranes, mass flow controller, microbalance, uncertainty.