ISO 11423-1:1997

Overview

ISO 11423-1:1997 defines a head-space gas chromatographic (HS-GC) method for the determination of benzene and some benzene derivatives in water. The method targets benzene, methylbenzene (toluene), dimethylbenzenes (xylenes) and ethylbenzene (commonly referred to as BTX) and may be applicable to other non‑polar compounds with similar properties. It is intended for homogeneous water and wastewater samples with concentrations above 2 µg/L (higher limits may apply for organically polluted matrices).

Key topics and requirements

• Method principle: Heat a defined volume of unfiltered water in a sealed vial to establish equilibrium between liquid and head-space gas, then transfer an aliquot of the gaseous phase to a gas chromatograph.
• Analytes: Benzene, toluene, ethylbenzene, o‑/m‑/p‑xylene (BTX); applicability to further derivatives must be verified for each sample.
• Sampling and sample prep:
  • Use non‑actinic glass containers or head-space vials; avoid plastics to prevent sorption/desorption.
  • For increased gas-phase partitioning, add potassium carbonate (example: ~7–8 g per 5 mL sample in vials) to boost ionic strength; neutralize CO2 in gaseous waters similarly.
  • Store samples at about 4 °C in the dark and analyse within 2 days when possible.
• Head-space conditions: Static equilibrium typically achieved at ≥60 °C for ≥1 hour; the same conditions must be used for samples and blanks.
• Chromatography and detection:
  • Use at least two capillary columns with different stationary phase polarity (simultaneous injection preferred) to confirm identity.
  • FID is the standard detector for quantification; GC‑MS or PID can be used for improved identification when needed.
  • Manual injection volumes recommended ≤ 1 µL (hot syringe warmed ~20 °C above head-space temperature).
• Quality control:
  • Perform reagent and air blanks covering the full analytical path; benzene ubiquity requires careful blank control.
  • Blank values normally should be