ISO 5667-26:2022

Overview

ISO 5667-26:2022 - "Water quality - Sampling - Part 26: Guidance on sampling for the parameters of the oceanic carbon dioxide system" provides standardized guidance for collecting discrete seawater samples suitable for analysis of the four measurable inorganic carbon parameters: total dissolved inorganic carbon (CT), total alkalinity (AT), pH, and CO2 fugacity (fCO2). The standard focuses on practical sampling from Niskin bottles or other water samplers and on steps that minimize gas exchange and biological alteration of carbonate chemistry.

Key topics and technical requirements

• Scope and principle
  • Collect discrete seawater samples to preserve CT, AT, pH and fCO2 for laboratory analysis.
  • Minimize gas exchange; add preservative (if used) before closing to avoid CO2 loss or uptake.
• Apparatus and materials
  • Use appropriate drawing tubing (e.g., Tygon; silicone when needed to avoid contamination).
  • Prefer borosilicate glass containers (e.g., Schott Duran) for CT and AT samples; gas-impermeable caps for fCO2.
  • Recommended cleaning: 1 M HCl bath (~24 h), rinse in Milli‑Q water (~24 h), then bake (e.g., 450 °C furnace for organic removal) as indicated.
• Sampling procedure
  • Rinse sample bottle and drawing tube with seawater; fill to minimize bubbles and headspace.
  • For fCO2 samples, include a small headspace (~1% of bottle volume) to avoid breakage during warming.
  • For CT and AT, use gas-tight closures - greased ground glass stoppers preferred; screw-cap bottles have been used but are not recommended for long-term storage.
  • Use mercuric chloride (HgCl2) reagent to prevent biological activity when required; add before final closure.
• Documentation, storage and QA
  • Record metadata (time, location, in-situ temperature, salinity, pressure) and sample handling.
  • The standard refers to quality assurance/quality control practices (see ISO 5667-14).

Applications and users

• Intended for oceanographers, marine chemists, environmental monitoring agencies, research vessels and laboratories conducting ocean carbon system surveys, ocean acidification studies, or baseline monitoring.
• Ensures comparability of measurements used to calculate seawater carbonate chemistry and to support climate and ecosystem impact research.
• Practical for field campaigns where reliable preservation of CT, AT, pH and fCO2 is critical.

Related standards

• ISO 5667-14 (quality assurance and quality control of environmental water sampling)
• Other parts of the ISO 5667 series for broader water sampling methods

Keywords: ISO 5667-26:2022, water quality sampling, oceanic carbon dioxide system, CT, AT, pH, fCO2, seawater sampling, Niskin bottle, mercuric chloride, borosilicate glass.