oSIST prEN 18337:2026

Food authenticity - Determination of 18O/16O isotope ratios in liquid aqueous food matrices by Equilibration - Isotope Ratio Mass Spectrometry (Eq-IRMS)

This document specifies a method for instrumental analysis by equilibration-isotope ratio mass spectrometry (Eq-IRMS) of liquid, aqueous food matrices to determine ¹⁸O/16O isotope ratios of the water of the product. The ¹⁸O/¹⁶O isotope ratios obtained by following this document are expressed as δ¹⁸O values relative to internationally recognised reference materials.
This document does not apply to sample preparation. It is assumed that the food sample has been pre-treated as necessary and homogenised.
Similarly, the interpretation of the obtained δ¹⁸O values is not covered by this document. Following this protocol will result only in isotope delta values for the sample materials.
Although other instrumental techniques can be applied to determine δ¹⁸O values in liquid, aqueous food materials, these other techniques are not covered by this document.

Lebensmittelauthentizität - Bestimmung des 18O/16O-Isotopenverhältnisses in flüssigen, wässrigen Lebensmittelmatrizes durch Equilibrations-Isotopenverhältnis-Massenspektrometrie (Eq-IRMS)

Dieses Dokument legt ein Verfahren zur instrumentellen Analyse mittels Gleichgewichts(Equilibrierungs)- Isotopenverhältnis-Massenspektrometrie (Eq-IRMS) von flüssigen, wässrigen Lebensmittelmatrices zur Bestimmung der 18O/16O-Isotopenverhältnisse des Wassers im Produkt fest. Die nach diesem Dokument ermittelten 18O/16O-Isotopenverhältnisse werden als δ18O-Werte bezogen auf international anerkannten Referenzmaterialien(RM) angegeben.
Dieses Dokument ist nicht auf die Probenvorbereitung anwendbar. Es wird davon ausgegangen, dass die Lebensmittelprobe entsprechend vorbehandelt und homogenisiert wurde.
Ebenso wird die Interpretation der erhaltenen δ18O-Werte in diesem Dokument nicht behandelt. Die Einhal
tung dieser Arbeitsvorschrift führt nur zu Isotopen-Delta-Werten für die Probenmaterialien.
Obwohl auch andere instrumentelle Techniken zur Bestimmung der δ18O-Werte in flüssigen, wässrigen Lebensmitteln angewendet werden können, werden diese anderen Techniken in diesem Dokument nicht behandelt.

Authenticité des aliments - Détermination des rapports isotopiques 18O/16O dans les matrices alimentaires liquides aqueuses par spectrométrie de masse des rapports isotopiques après équilibrage (Eq-SMRI)

Le présent document spécifie une méthode d'analyse instrumentale par spectrométrie de masse des
rapports isotopiques après équilibrage (Eq-SMRI) de matrices alimentaires liquides aqueuses pour déterminer les rapports isotopiques 18O/16O de l'eau du produit. Les rapports isotopiques 18O/16O
obtenus en suivant le présent document sont exprimés en valeurs δ18O par rapport aux matériaux de référence (MR) internationalement reconnus.
Le présent document ne s'applique pas à la préparation de l'échantillon. On suppose que l'échantillon d'aliment a été prétraité au besoin et homogénéisé.
De même, l'interprétation des valeurs δ18O obtenues n'est pas couverte par le présent document. Le respect de ce protocole n'aboutira qu'à l'obtention des déviations isotopiques pour les échantillons.
Bien que d'autres techniques instrumentales puissent être appliquées pour déterminer les valeurs δ18O dans les denrées alimentaires liquides aqueuses, ces autres techniques ne sont pas couvertes par le présent document.

Pristnost živil - Določanje izotopskih razmerij ¹⁸O/¹⁶O v tekočih vodnih živilskih matricah z metodo ravnotežne izotopske razmerne masne spektrometrije (Eq-IRMS)

Ta dokument določa metodo za instrumentalno analizo z masno spektrometrijo izotopskih razmerij z izravnavo (Eq-IRMS) tekočih, vodnih živilskih matric za določanje izotopskih razmerij ¹⁸O/¹⁶O vode v izdelku. Izotopska razmerja ¹⁸O/¹⁶O, pridobljena v skladu s tem dokumentom, so izražena kot vrednosti δ¹⁸O glede na mednarodno priznane referenčne materiale.
Ta dokument se ne nanaša na pripravo vzorcev. Predpostavlja se, da je bil živilski vzorec predhodno obdelan po potrebi in homogeniziran.
Prav tako interpretacija pridobljenih vrednosti δ¹⁸O ni zajeta v tem dokumentu. Sledenje temu protokolu bo prineslo le izotopske delta vrednosti za vzorčne materiale.
Čeprav se lahko uporabijo tudi druge instrumentalne tehnike za določanje vrednosti δ¹⁸O v tekočih, vodnih živilskih materialih, te druge tehnike niso zajete v tem dokumentu.

General Information

• Status: Not Published
• Public Enquiry End Date: 30-May-2026
• ICS: 67.050 - General methods of tests and analysis for food products
• Technical Committee: KŽP - Agricultural food products
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 09-Apr-2026
• Due Date: 27-Aug-2026
• Ref Project: prEN 18337 - Food authenticity - Determination of 18O/16O isotope ratios in liquid aqueous food matrices by Equilibration - Isotope Ratio Mass Spectrometry (Eq-IRMS)

Overview

oSIST prEN 18337:2026 is a draft European standard developed by CEN/TC 460 for the instrumental analysis of food authenticity. It specifies a robust method to determine the ratio of stable oxygen isotopes ¹⁸O/¹⁶O in the water component of liquid, aqueous food matrices. The determination uses Equilibration–Isotope Ratio Mass Spectrometry (Eq-IRMS), providing results as δ¹⁸O values referenced to internationally recognized standards. The scope is analytical measurement only-sample preparation and interpretation of the resulting δ¹⁸O values fall outside this standard.

This standard offers an authoritative tool to enhance food supply transparency, track authenticity, and combat fraudulent labeling in the food sector through isotope ratio analysis.

Key Topics

• Food Authenticity Testing: The standard addresses the need for precise and reproducible determination of food origin and composition through stable isotope analysis, supporting authenticity claims and detection of adulteration.

• Eq-IRMS Technique: Outlines the use of equilibration with a CO₂/helium headspace and subsequent measurement by Isotope Ratio Mass Spectrometry, focusing on isotopic equilibrium, sample handling, and international normalization.

• Normalization to Reference Standards: Results are calibrated to the VSMOW/SLAP (Vienna Standard Mean Ocean Water / Standard Light Antarctic Precipitation) scale, ensuring comparability and traceability to globally accepted reference materials.

• Quality Control and Assurance: The structured procedure includes requirements for quality control materials and performance checks to identify drift, memory effects, and instrument stability, safeguarding result reliability.

• Reporting Requirements: Details data processing, normalization, and documentation to ensure outputs are comprehensive and internationally compatible.

Applications

The method specified in oSIST prEN 18337:2026 enables reliable measurement of δ¹⁸O values in the water fraction of a variety of liquid food products:

• Authenticity Verification: Critical for confirming geographic or botanical origin claims, such as distinguishing between authentic versus adulterated juices, wines, or bottled water.
• Detection of Adulteration: Supports uncovering practices such as dilution or mislabeling of premium products by identifying isotopic discrepancies.
• Quality Control in Food Trade: Assists regulatory bodies and quality assurance laboratories in monitoring compliance with food labeling regulations.
• Research and Development: Useful in food science research for tracking water movement within supply chains and evaluating new authenticity markers.

Adopting this standard can strengthen consumer trust, uphold regulatory compliance, and protect brands from food fraud.

Related Standards

The following standards and guidelines are closely related to oSIST prEN 18337:2026 and can offer additional methodological support:

• OIV-MA-AS2-12: Method for ¹⁸O/¹⁶O isotope ratio determination in water from wines and must (Organisation Internationale de la Vigne et du Vin).
• OIV-OENO 662H-2022: Method for determining ¹⁸O/¹⁶O isotope ratios in grape juice.
• EN 17958:2024: Stable isotope ratio analysis in food authentication (providing foundational definitions and data handling principles).
• ISO and IAEA Guidance: Use of international reference waters VSMOW2 and SLAP2 for isotope ratio normalization.

Summary

oSIST prEN 18337:2026 supports the food industry and regulatory agencies in enhancing food authenticity testing through the precise measurement of ¹⁸O/¹⁶O isotope ratios in aqueous food matrices using Eq-IRMS. By following this European standard, organizations can achieve internationally comparable results, improve traceability, and contribute to the fight against food fraud, ultimately ensuring a trustworthy food supply chain.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2026
Pristnost živil - Določanje izotopskih razmerij ¹⁸O/¹⁶O v tekočih vodnih živilskih
matricah z metodo ravnotežne izotopske razmerne masne spektrometrije (Eq-
IRMS)
Food authenticity - Determination of 18O/16O isotope ratios in liquid aqueous food
matrices by Equilibration - Isotope Ratio Mass Spectrometry (Eq-IRMS)
Lebensmittelauthentizität - Bestimmung des 18O/16O-Isotopenverhältnisses in flüssigen,
wässrigen Lebensmittelmatrizes durch Equilibrations-Isotopenverhältnis-
Massenspektrometrie (Eq-IRMS)
Authenticité des aliments - Détermination des rapports isotopiques 18O/16O dans les
matrices alimentaires liquides aqueuses par spectrométrie de masse des rapports
isotopiques après équilibrage (Eq-SMRI)
Ta slovenski standard je istoveten z: prEN 18337
ICS:
67.050 Splošne preskusne in General methods of tests and
analizne metode za živilske analysis for food products
proizvode
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2026
ICS 67.050
English Version
18 16
Food authenticity - Determination of O/ O isotope ratios
in liquid aqueous food matrices by Equilibration - Isotope
Ratio Mass Spectrometry (Eq-IRMS)
18 16
Authenticité des aliments - Détermination des rapports Lebensmittelauthentizität - Bestimmung des O/ O-
18 16
isotopiques O/ O dans les matrices alimentaires Isotopenverhältnisses in flüssigen, wässrigen
liquides aqueuses par spectrométrie de masse des Lebensmittelmatrizes durch Equilibrations-
rapports isotopiques après équilibrage (Eq-SMRI) Isotopenverhältnis-Massenspektrometrie (Eq-IRMS)
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 460.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATIO N

EUROPÄISCHES KOMITEE FÜR NORMUN G

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 18337:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 7
5 Reagents . 8
6 Apparatus . 9
7 Procedure . 10
7.1 Prerequisites . 10
7.2 Sequence design . 10
7.3 Instrumental tests . 11
7.3.1 General. 11
7.3.2 Backgrounds . 11
7.3.3 Stability of working gas CO . 11
7.3.4 Linearity of working gas CO . 11
7.4 Equilibration. 11
sample gas . 12
7.5 Headspace sampling and purification of CO2
7.6 Instrumental IRMS analysis . 12
7.7 Data processing . 13
7.7.1 General. 13
7.7.2 Rejection of individual runs within a sequence . 13
7.7.3 Data to record. 13
7.7.4 Evaluation of δ O values . 13
raw
7.7.5 Normalization . 14
7.7.6 Rejection of individual samples within a sequence . 15
7.7.7 Rejection of entire sequences . 15
8 Precision . 15
8.1 General. 15
8.2 Repeatability . 15
8.3 Reproducibility . 16
8.4 Uncertainty. 17
9 Expression of results . 17
10 Test report . 18
Annex A (informative) Experimental equilibration conditions in this interlaboratory validation
study . 19
Annex B (informative) Interlaboratory validation study of the method . 20
Bibliography . 22

European foreword
This document (prEN 18337:2026) has been prepared by Technical Committee CEN/TC 460 “Food
Authenticity”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
Introduction
This document concerns an instrumental method for the determination of oxygen isotope delta values in
liquid, aqueous food matrices.
The stable isotope ratio of oxygen usually is expressed as an isotope delta value (δ) which is the ratio of
18 16
the heavier isotope ( O) to the lighter isotope ( O) in a particular sample relative to the same ratio
within an agreed reference.
Originally, the method was developed for the analysis of pure water samples, but the suitability to food
matrices has been shown in numerous publications. [1, 2, 3]
18 16 18 16
For the determination of the O/ O isotope ratio in wine and must, the “Method for O/ O isotope ratio
determination of water in wines and must” (OIV-MA-AS2-12) as well as for grape juice the “Method for
18 16
O/ O isotopic ratio determination of water in grape juice (Resolution OIV-OENO 662H-2022) are
available as reference methods of the Organisation Internationale de la Vigne et du Vin (OIV). [3]
Oxygen stable isotope ratios in the aqueous fraction of food samples can provide information regarding
the procedural or geographic origin of food. It has the potential to reveal information on adulteration
such as watering or mislabelling of the geographic origin.
As the setup of the required apparatus depends to a large extent on its design principles and the specific
recommendations by the manufacturers which have to be followed, it is intended to serve as a frame in
which the analysts can define their own analytical work in accordance with the standard procedure.

Numbers in square brackets refer to the Bibliography.
1 Scope
This document specifies a method for instrumental analysis by equilibration-isotope ratio mass
18 16
spectrometry (Eq-IRMS) of liquid, aqueous food matrices to determine O/ O isotope ratios of the water
18 16 18
of the product. The O/ O isotope ratios obtained by following this document are expressed as δ O
values relative to internationally recognized reference materials (RM).
This document does not apply to sample preparation. It is assumed that the food sample has been pre-
treated as necessary and homogenized.
Similarly, the interpretation of the obtained δ O values is not covered by this document. Following this
protocol will result only in isotope delta values for the sample materials.
Although other instrumental techniques can be applied to determine δ O values in liquid, aqueous food
materials, these other techniques are not covered by this document.
2 Normative references
There are no normative references in this document.
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
isotope delta value
δ
stable isotope ratio of a material expressed relative to a reference
Note 1 to entry: For carbon, this expression is given in Formula (1):

13 12 (1)
R C/ C
( )
sample
13 12
δ C/ C sample −1
( )
( )
ref
13 12
R C/ C
( )
ref
13 12 1
Note 2 to entry: The term δ ( C/ C) is often changed from the IUPAC format to δ C . This document uses the
ref ref
IUPAC format for familiarity.
Note 3 to entry: To ensure international comparability of isotope delta values, a common reference is used; this
reference is an international measurement standard assigned by convention with an isotope delta value exactly
equal to zero.
Note 4 to entry: Carbon isotope delta values for natural isotopic abundance in food materials are small and
expressed in permille (‰) rather than in their native form.
[SOURCE: EN 17958:2024, 3.1]
=
3.2
Vienna Standard Mean Ocean Water
VSMOW
agreed reference for stable oxygen isotope ratios
Note 1 to entry: The δ O value of this international measurement standard assigned by convention is exactly equal
to zero (0 ‰). [4, 5]
Note 2 to entry: VSMOW is no longer available as an existing material and has been replaced by the international
standard VSMOW2 which is now applied for normalization to the VSMOW/SLAP scale in practice.
3.3
Standard Light Antarctic Precipitation
SLAP
reference material close to the lower end of the range of abundances of δ O of natural occurring
materials, introduced by the International Atomic Energy Agency (IAEA) to take into account oxygen
isotope scale effects
Note 1 to entry: A consensus δ O value of −55,5 ‰ was adopted. [5]
3.4
VSMOW/SLAP oxygen isotope delta scale
defined by the exact isotope delta values assigned to VSMOW (δ O = 0 ‰) and SLAP
VSMOW/SLAP
(δ OVSMOW/SLAP = −55,5 ‰), respectively
2 18
Note 1 to entry: The reporting scales for δ H and δ O are still denoted and referred to as VSMOW/SLAP scales,
despite the exhaustion of supply of VSMOW and SLAP and their replacement by the two new international
measurement standards VSMOW2 and SLAP2. [6]
Note 2 to entry: To ensure traceability to the VSMOW/SLAP scale, oxygen isotope delta values shall be normalized
using two or more reference materials to account for scale effects during measurement (see 7.7.4). [4]
Note 3 to entry: Determination of the oxygen stable isotope ratio for the purposes of this method includes
normalization of the measured values to the VSMOW/SLAP scale.
3.5
δ O
raw
δ O value calculated by the IRMS instrument software, standardised to the CO monitoring gas, prior to
normalisation to a reference
3.6
δ O
VSMOW/SLAP
δ O value normalised to the VSMOW/SLAP oxygen isotope delta scale
3.7
equilibration gas
) in helium used to flush the headspace above the liquid sample in the
gas mixture of carbon dioxide (CO2
sample vials
Note 1 to entry: An oxygen isotope equilibrium is established between the CO of the equilibration gas and the
water of the aqueous sample.
3.8
sample gas CO
CO present in the gas mixture of the sample vial’s headspace after isotopic equilibration of the aqueous
sample with the equilibration gas
Note 1 to entry: The sample gas CO2 is separated from further volatile components of the headspace gas mixture
and transferred to the IRMS for determination of the oxygen stable isotope ratio.
3.9
working gas
cylinder gas
monitoring gas
DEPRECATED: reference gas
gas consisting of the same molecule as the sample gas (i.e. CO or N ) but introduced directly into the
2 2
mass spectrometer from a high-pressure cylinder rather than being created from a solid/liquid sample
material within the elemental analyser
Note 1 to entry: An isotope delta value with a working gas within its traceability chain to the international
measurement standard will require normalization using reference materials of known isotope delta analysed in the
same sequence before the isotope delta value lies on the international scale.
3.10
equilibration time
time specified in the method to ensure isotopic equilibrium
Note 1 to entry: To ensure isotopic equilibrium, the equilibration time within the method shall be longer than the
minimum time required to reach equilibrium.
3.11
sequence
continuous set of analyses including reference materials for normalization, QA/QC materials, procedural
blanks and samples prepared and analyzed together
[SOURCE: EN 17958:2024, 3.5]
4 Principle
The headspace over the liquid sample in a gas-tight sample vial is flushed with a gas mixture of CO in
helium (equilibration gas). The closed two-phase system is equilibrated for several hours at a constant
temperature, resulting in an oxygen isotope equilibrium between the carbon dioxide in the gas phase and
the liquid, aqueous food matrix.
16 18 16 18 16
C O + H O ⇌ C O O + H O
2 2 2
An aliquot of the equilibrated gas mixture is extracted from the headspace and dried online. CO sample
gas is separated from other volatile components of the gas mixture and transferred online into the isotope
ratio mass spectrometer. The gas molecules are ionized in an electron impact (EI) ion source and the
major isotopologue ions of the molecular ion are measured. After acceleration by a static electric field,
ions are separated in a momentum. The separator is usually an electromagnet, although permanent
magnets have also been used.
The ions are detected in a set of detectors (mostly Faraday cups), which simultaneously collect ions with
18 16
m/z values of 44, 45 and 46. From the ratio of the ion intensities the O/ O isotope ratio is calculated.
13 17
The intensity of m/z = 45 is used to correct for the contributions of C and O isotopes to the intensity
of m/z = 46. The δ O values are calculated by the IRMS instrument’s software by standardization to
raw
the CO working gas.
To take into account scale effects a correction by using RMs of different isotope ratios is required – a
process termed “normalisation.” The analysis of RMs (see 5.5) within the same sequence as samples
allows the linking of the raw δ O value to the zero-point of the oxygen isotope delta scale (VSMOW/SLAP
scale). More details can be found in 7.7.4.
Isotope delta values normalized on the VSMOW/SLAP scale are the output of following this document.
NOTE Normalization can also be referred to as calibration.
5 Reagents
Unless otherwise stated, use only reagents of recognized analytical grade.
5.1 Helium carrier gas, required helium purity is given by instrumentation manufacturer,
typically > 99,995 %.
5.2 CO working gas, required CO purity is given by instrumentation manufacturer,
2 2
typically > 99,9 %.
5.3 CO in helium, required purity and CO content is given by instrumentation manufacturer, typically
2 2
0,3 % vol or 5 % vol.
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5.4 Preservative agent, which do not affect the O/ O isotope ratio, such as sodium azide, benzoic
acid or potassium sorbate.
NOTE Alternatively, 0,22 µm pore diameter filters can be applied for sterilization.
5.5 RMs for normalization
5.5.1 International Reference Standard Water - VSMOW2, SLAP2 and GRESP
The international measurement materials VSMOW2 and SLAP2 are intended for normalization purpose
2 1 18 16
and provide water standards with reference values of the relative difference in H/ H and O/ O
isotope-amount ratios referred to the VSMOW–SLAP δ-scale. [7]
A further international reference standard water, Greenland Summit Precipitation (GRESP), is available
to verify normalization with VSMOW2 and SLAP2. [8]
Assigned δ-values are [7,8]:
— Vienna Standard Mean Ocean Water 2 (VSMOW2): δ O = 0 ‰
VSMOW/SLAP
— Standard Light Antarctic Precipitation 2 (SLAP2): δ O = −55,5 ‰
VSMOW/SLAP
— Greenland Summit Precipitation (GRESP): δ O = −33,4 ‰
VSMOW/SLAP
NOTE 1 The above listed international reference standard waters are available in Europe from the International
Atomic Energy Agency (IAEA). Their availability is limited to three orders in three years. The international reference
standard waters are recommended only for direct use immediately upon opening; the IAEA's instructions for use
are to be followed. “Users are strongly advised to prepare their own internal reference materials for daily use and
calibrate those standards against these international standards and reference materials.”[7, 8] The in-house RMs,
in turn, are used to normalize the δ O-values of the unknown samples and thus trace them back to the
VSMOW/SLAP scale.
NOTE 2 Further international RMs with proven traceability to the VSMOW/SLAP scale can be found in a list of
RMs maintained by International Union of Pure and Applied Chemistry (IUPAC) [4]. As the IUPAC list is not
frequently updated, other RMs which have demonstrable traceability to either the international measurement
standard, or to other RMs within the IUPAC report can be used. The Reston Stable Isotope Laboratory (RSIL) of the
United States Geological Survey (USGS) also provides isotopic RMs, which are suitable for use in calibration. [9]
5.5.2 RMs, shall have demonstrable traceability to the VSMOW/SLAP scale.
Each analytical sequence shall include replicates of at least two different RMs, typically water, to be used
for normalization of δ O values to the VSMOW/SLAP scale. RMs should span the range of isotope delta
raw
expected for samples. If this is not possible, then the wider the range of isotope delta covered, the smaller
the additional uncertainty introduced by extrapolation.
NOTE Certain food matrices provide δ O values above 0 ‰, which are outside the δ-range of the international
reference standard waters VSMOW2 and SLAP2 (e.g. direct orange juice). International RMs with positive δ O
18 18
values are available, for example USGS 50 (δ O = +4,95 ‰) or USGS 53 (δ O = +5,47 ‰) [9].
VSMOW/SLAP VSMOW/SLAP
RMs may be characterized isotopically in-house [10] or may be purchased commercially with an assigned
δ O value.
VSMOW/SLAP
RMs shall be stored in a manner that fractionation of oxygen isotopes is avoided.
5.6 Quality assurance/control (QA/QC)
For QC samples additional materials are needed within each measurement sequence. When possible,
these should include matrix-matched material for different the sample materials.
18 18
For samples with δ O values not covered by the δ-range of RMs, QC samples with comparable δ O values,
when possible, should be used to check the validity of the extrapolation.
RMs with an assigned δ O for QA/QC may be characterized in-house [10] or may be
VSMOW/SLAP
commercially available.
QC materials shall be stored in a manner that fractionation of oxygen isotopes is avoided.
6 Apparatus
6.1 Volumetric pipette, typically, a plunger-operated pipette with appropriate tips, e.g. for volume
between 0,1 mL and 0,5 mL.
6.2 Sterile filters, optional: 0,22 µm pore diameter filters if applied for sterilization.
6.3 Folded filter papers, optional: folded filter papers, e.g. medium filtration speed, retention capacity
4 µm to 12 µm, if applied to remove CO from sparkling fluids.
6.4 Ultrasonic bath, optional: if applied to remove CO from sparkling fluids.
6.5 Gas tight sample vials, sample vials for equilibration with screw caps with gas-tight septa, e.g.
chlorobutyl septa. Required sample vial volume is given by instrumentation manufacturer.
6.6 IRMS instrument in combination with an equilibration unit
6.6.1 General
Typically, a continuous flow instrument is applied for transferring the CO , working gas and sample gas,
into the isotope ratio mass spectrometer. Dual inlet systems can be used if they meet the performance
criteria of the continuous flow method.
6.6.2 Isotope Ratio Mass Spectrometer with a continuous flow system, isotope ratio mass
spectrometer (IRMS) suitable for the analysis of carbon dioxide, equipped with a triple collector that
simultaneously detects the ions with m/z = 44, 45, and 46. The IRMS is equipped with a continuous flow
system that feeds both the purified sample gas CO as well as the CO working gas into the isotope ratio
2 2
mass spectrometer.
6.6.3 Temperature controlled equilibration unit with autosampler and IRMS interface
The equilibration unit regulates sample flushing with equilibration gas, the isotopic equilibration
procedure at a constant temperature, sampling and purification of the sample gas CO . Typically, this
happens in a temperature-controlled tray, where the samples are flushed automatically with
equilibration gas. The vial’s headspace is sampled using an autosampler. The gas mixture is dried, e.g.
applying a gas drying membrane or chemical trap. Subsequently, CO sample gas is isolated from other
volatiles, e.g. by a packed or capillary GC column, or a purge and trap column, and transferred online into
the isotope ratio mass spectrometer by means of the continuous flow system.
NOTE Types of apparatus and materials are given for informational purposes and can be replaced by items
with similar performance but meeting stated requirements of this document.
7 Procedure
7.1 Prerequisites
RMs for normalization, matrix match
...