Overview
ISO 11423-2:1997 - "Water quality - Determination of benzene and some derivatives - Part 2: Method using extraction and gas chromatography" - specifies an extraction-based laboratory procedure for measuring benzene, toluene, ethylbenzene and xylenes (BTX) and similar nonpolar aromatic compounds in water and wastewater. The method combines liquid–liquid extraction (commonly with pentane) and analysis by gas chromatography (GC) using capillary columns and a flame ionization detector (FID). This part complements ISO 11423-1 (head-space GC) and is chosen based on sample type and available instrumentation.
Key Topics and Requirements
- Analytes covered: Benzene, methylbenzene (toluene), 1,2/1,3/1,4-dimethylbenzenes (xylenes) and ethylbenzene (BTX); additional nonpolar compounds with similar boiling points may be tested after validation.
- Sample handling: Collect in non-actinic glass conical-shoulder bottles; avoid plastics; cool samples and start extraction within 2 days or store at 4 °C in the dark.
- Extraction: Liquid–liquid extraction with a nonpolar solvent (e.g., pentane); recommended phase ratios depend on expected concentration. Use magnetic stirring, mechanical shaking or manual shaking; minimize losses by cooling during extraction.
- Separation: Analyze extracts by GC on at least two capillary columns with different stationary-phase polarities (simultaneous injection recommended) to improve identification and reduce peak overlap.
- Detection: Flame ionization detector (FID) is standard; selective detectors (GC–MS, PID) may be used for improved compound identification.
- Quality control: Perform blank determinations (including sampling-to-evaluation steps); deduct blank only when statistically appropriate. Use internal standards (e.g., toluene‑d8) or external calibration; three calibration approaches described: GC-only, total method external, total method internal.
- Interferences & limitations: Evaporation/stripping losses, contamination from ambient air, sorption to plastics, surfactants/emulsions, suspended solids, and co-eluting hydrocarbons (e.g., mineral oil) can impair results. Use additional columns or selective detectors where necessary.
- Reagents & equipment: Pentane purified and checked for BTX absence; microseparator and quartz wool for small organic-phase volumes; standard GC consumables and operating gases.
Applications and Users
- Environmental testing laboratories performing water quality analysis for BTX compounds in drinking water, surface water, groundwater and wastewater.
- Regulators and compliance labs monitoring aromatic hydrocarbon contamination and industrial effluents.
- Researchers validating pollutant occurrence, remediation efficacy or routine monitoring programs that require solvent-extraction GC methods.
Related Standards
- ISO 11423-1 - Head-space gas chromatographic method for benzene and derivatives (alternative technique).
- ISO/TC 147 (Water quality) - technical committee responsible for the standard.
Keywords: ISO 11423-2, water quality, benzene determination, BTX analysis, extraction GC, pentane extraction, flame ionization detector, capillary columns, water monitoring.