ISO 5667-26:2022

Water quality - Sampling - Part 26: Guidance on sampling for the parameters of the oceanic carbon dioxide system

This document specifies how to collect discrete seawater samples, from a Niskin or other water sampler, that are suitable for the analysis of the four measurable inorganic carbon parameters: total dissolved inorganic carbon, total alkalinity, pH and CO2 fugacity.

Qualité de l’eau – Echantillonnage — Partie 26: Lignes directrices pour l’échantillonnage d’eau de mer en vue de l’analyse des formes du carbone

General Information

• Status: Published
• Publication Date: 02-Nov-2022
• ICS: 13.060.45 - Examination of water in general
• Technical Committee: ISO/TC 147/SC 6 - Sampling (general methods)
• Drafting Committee: ISO/TC 147/SC 6/WG 15 - Sampling for oceanic carbon dioxide in sea water
• Current Stage: 6060 - International Standard published
• Start Date: 03-Nov-2022
• Due Date: 26-Jul-2022
• Completion Date: 03-Nov-2022

Relations

• Consolidated By: ISO 2400:2025 - Non-destructive testing - Ultrasonic testing - Specification for standard block No. 1
• Effective Date: 29-Jul-2023

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.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 5667-26
First edition
2022-11
Water quality — Sampling —
Part 26:
Guidance on sampling for the
parameters of the oceanic carbon
dioxide system
Qualité de l’eau – Echantillonnage —
Partie 26: Lignes directrices pour l’échantillonnage d’eau de mer en
vue de l’analyse des formes du carbone
Reference number
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 3
5.1 General . 3
5.2 Drawing tube . 3
5.3 Sample container . 3
5.3.1 General . 3
5.3.2 Samples for f measurement . 4
CO2
5.3.3 Samples for C and A measurement . 4
T T
5.3.4 Samples for pH measurement . 4
5.4 Mercury dispenser . 4
6 Reagent: Mercuric chloride solution, HgCl . 4
7 Procedure .5
7.1 General . 5
7.2 Filling procedure . 5
7.2.1 Rinse the sample bottle . 5
7.2.2 Fill the sample bottle . 5
7.2.3 Adjust the headspace . 5
7.2.4 Prevent biological activity in the sample . 5
7.2.5 Close the bottle . 6
7.2.6 Secure the lid . 6
7.3 Sample storage . 6
7.4 Sample documentation . 6
8 Assurance and quality control . 7
Annex A (informative) Determination of the size of a headspace in the sample bottle .8
Bibliography .11
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 6,
Sampling (general methods).
A list of all parts in the ISO 5667 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
The ocean is currently absorbing about one quarter of the carbon dioxide that humans are emitting.
When carbon dioxide combines with seawater, chemical reactions occur that reduce the seawater pH,
hence the term ocean acidification. Acidification can affect many marine organisms, but especially
those that build their shells and skeletons from calcium carbonate. Over the past few years, several
high-profile reports have highlighted the urgent need to better understand the effects of changes in
carbonate chemistry on marine organisms and ecosystems. Research in this field was limited to a few
groups around the world until recently but the number of scientists involved in ocean acidification
research has been rapidly rising over the past few years. The reliable characterization and manipulation
of the carbonate system involves good analytical skills and measuring facilities and continuous
monitoring of seawater chemistry in the field and during experimentation. The predictive power of
field surveys and the robustness of results from experiments critically depend on proper sampling and
experimental protocols.
The oceanic carbonate system can be described by measuring at least two parameters of the following
four parameters, total dissolved inorganic carbon (C ), total alkalinity (A ), fugacity of carbon dioxide
T T
( f ) and pH in seawater. This document describes how to collect and preserve discrete seawater
CO2
samples, from a Niskin bottle or other water samplers, for the analysis of four measurable inorganic
carbon parameters including: C A f and pH, according to highest standard levels accepted by
T, T, CO2
global ocean carbon community.
NOTE This document is based on Reference [5].
v
INTERNATIONAL STANDARD ISO 5667-26:2022(E)
Water quality — Sampling —
Part 26:
Guidance on sampling for the parameters of the oceanic
carbon dioxide system
1 Scope
This document specifies how to collect discrete seawater samples, from a Niskin or other water sampler,
that are suitable for the analysis of the four measurable inorganic carbon parameters: total dissolved
inorganic carbon, total alkalinity, pH and CO fugacity.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5667-14, Water quality — Sampling — Part 14: Guidance on quality assurance and quality control of
environmental water sampling and handling
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
total alkalinity
A
T
number of moles of hydrogen ion equivalent to the excess of proton acceptors (bases
–4,5
formed from weak acids with a dissociation constant K ≤ 10 at 25 °C and zero ionic strength) over
–4,5
proton donors (acids with K > 10 ) in 1 kg of sample
Note 1 to entry: The formula to determine A is:
T
− −
−−2 −−2 3− −
   
           
A = HCOC+22OB+ ()OH + OH + HPOP+ O + SiOO()HN+[]HH+ S +…
T 33 4 44 3
4 3
               
+−
   
− HH− SO −[]HFFH−[]PO −…
4 34
   
F
+
Note 2 to entry: The brackets represent total concentrations of these constituents in solution, [H ] is the free
F
concentration of hydrogen ion and the ellipses stand for additional minor acid or base species that are either
unidentified or present in such small amounts that they can be safely neglected. In open ocean water, the
–
concentrations of NH and HS are typically so low that they can be neglected; they may, however, be significant
in anoxic environments.
3.2
total dissolved inorganic carbon
C
T
dissolved inorganic carbon content of sea water is defined as
* −−2
     
C = CO + HCOC+ O
T 23 3
     
–1
where the brackets represent total concentrations of these constituents in solution (in µmol kg ) and
[CO *] represents the total concentration of all unionized carbon dioxide, whether present as H CO or
2 2 3
as CO
3.3
fugacity
f
chemical potential of an individual component of a vapor phase
Note 1 to entry: The fugacity of carbon dioxide, f , is not the same as its partial pressure the product of mole
CO2
fraction and total pressure,xp. but rather takes account of the non-ideal nature of the gas phase. The fugacity
CO2
of gas such as CO can be determined from knowledge of its formula of state:
p
 
 
fx=−.p exp ()VRTp''dp
CO2CO2 CO2
∫
RT
 
 0 
where
x is the mole fraction of CO ;
CO2 2
p is the total pressure;
p' is the partial pressure of CO ;
V is the volume of CO ;
CO2 2
−1 −1
R is the molar gas constant which is 8.31446261815324 J K mol ;
T is the temperature in kelvin.
It should be noted that to apply the results of four measurable inorganic carbon parameters to calculate carbonate
chemistry of seawater, the in-situ temperature, pressure, salinity as well as phosphate and silicate concentration
of the seawater may need to be measured.
3.4
total hydrogen ion concentration
total hydrogen ion concentration of sea water is defined as:
++
   
HH= ()1+SK/
TS
   
F
+−
   
≈ HH+ SO
   
F
where
+
[H ] is the free concentration of hydrogen ion in sea water;
F
− 2−
S is the total sulfate concentration ([HSO ]+[SO ]);
T 4 4
−
K is the acid dissociation constant for HSO
S 4
3.5
pH
negative of the base 10 logarithm of the hydrogen ion concentration:
+
 
pH=−logH
 
+
–1
 
where H is the hydrogen ion concentration, expressed in expressed in mol kg-soln
 
4 Principle
For the analysis of A , C , pH and f in seawater, samples are collected in clean glass containers in a
T T CO2
manner designed to minimize gas exchange with the atmosphere.
NOTE CO exchange affects the various carbon parameters to differing degrees ranging from the very
sensitive CO fugacity, f , to alkalinity which is not affected by gas exchange.
2 CO2
If the sample is treated with a mercuric chloride solution to prevent biological activity, this occurs
prior to the container being closed to prevent exchange of carbon dioxide or water vapour with the
atmosphere.
5 Apparatus
5.1 General
The sample containers are somewhat different depending on which parameter is being collected, but
the basic concept is similar for the four possible inorganic carbon samples. In general, a flexible plastic
drawing tube, a clean glass sample container with stoppers, a container and dispenser for the mercuric
chloride solution (if it is being used) and a sampling log to record when and where each of the samples
were collected.
5.2 Drawing tube
® 1)
Tygon tubing is normally used to transfer the sample from the Niskin water sampler to the sample
container (5.3); however, if dissolved organic carbon samples are being collected from the same Niskins, ®
then it may be necessary to use silicone tubing to prevent contamination from the Tygon . The drawing
tube can be pre-treated by soaking in clean seawater for at least one day. This minimizes the amount of
bubble formation in the tube when drawing a sample.
5.3 Sample container
5.3.1 General
Sample containers depends on the parameter being measured, volume of sample required for analysis,
length of anticipated storage and collection method. Important considerations in bottle choice include
[1]
volume, leaching of bottle material, gas permeability, opening size, neck size, and sealing . Ideally,
sample containers should be prepared by cleaning in a 1 M HCl bath for approximately 24 h, followed by
−1
rinsing for approximately 24 h in Milli-Q water (18,2 MΩ cm resistivity). However, care shall be taken
to remove all residual acid during rinsing. Then, containars should be wrapped in aluminium foil and
placed in a 450 °C muffle furnace for 4 h to remove organic carbon. ®
1) Tygon tubing is an example of a suitable product available commercially. This information is given for the

convenience of users of this document and does not constitute an endorsement by ISO of this product.
5.3.2 Samples for f measurement
CO2
Typically, the f samples are analysed directly fr
...