EN ISO 7097-1:2026

• Abstract:

  This document describes an analytical method for the determination of uranium in samples from pure product materials such as U metal, UO2, UO3, uranyl nitrate hexahydrate, uranium hexafluoride and U3O8 from the nuclear fuel cycle. This procedure is sufficiently accurate and precise to be used for nuclear materials accountability. This method can be used directly for the analysis of most uranium and uranium oxide nuclear reactor fuels, either irradiated or un-irradiated, and of uranium nitrate product solutions. Fission products equivalent to up to 10 % burn-up of heavy atoms do not interfere, and other elements which could cause interference are not normally present in sufficient quantity to affect the result significantly. The method recommends that an aliquot of sample is weighed and that a mass titration is used, in order to obtain improved precision and accuracy. This does not preclude the use of alternative techniques which could give equivalent performance. The use of automatic device(s) in the performance of some critical steps of the method has some advantages, mainly in the case of routine analysis.

• Status: Published
• Publication Date: 18-Aug-2026
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: CEN/TC 430 - Nuclear energy, nuclear technologies, and radiological protection
• Drafting Committee: CEN/TC 430 - Nuclear energy, nuclear technologies, and radiological protection
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 19-Aug-2026
• Due Date: 19-Jun-2028
• Completion Date: 19-Aug-2026
• Ref Project: SIST EN ISO 7097-1:2026 - Nuclear fuel technology - Determination of uranium in solutions, uranium hexafluoride and solids - Part 1: Iron(II) reduction/potassium dichromate oxidation titrimetric method (ISO 7097-1:2025)

EN ISO 7097-1:2026 is a CEN European Standard for nuclear fuel technology that specifies an iron(II) reduction/potassium dichromate oxidation titrimetric method for determining uranium in solutions, uranium hexafluoride and solids. It is written for nuclear fuel cycle materials and for laboratories that need uranium results with the accuracy and precision used for nuclear materials accountability.

What does EN ISO 7097-1:2026 specify?

EN ISO 7097-1:2026 specifies an analytical method for uranium in pure product materials such as U metal, UO2, UO3, uranyl nitrate hexahydrate, uranium hexafluoride and U3O8. The method is also stated to be usable directly for most uranium and uranium oxide reactor fuels, irradiated or unirradiated, and for uranium nitrate product solutions.

The document is organized into clauses on scope, references, terms, principle, reactions and interferences, reagents, apparatus, sample preparation, procedure, result expression and test reporting. It also has two annexes that separate uranium hexafluoride handling from the way results are expressed for different sample types.

Annex	What it covers
Annex A	Uranium hexafluoride sampling and preparation of the test solution
Annex B	Expression of results for samples

What are the key requirements of EN ISO 7097-1:2026?

Measurement principle

EN ISO 7097-1:2026 uses a redox titration sequence: uranium(VI) is reduced to uranium(IV) with iron(II) sulfate in concentrated phosphoric acid, then the excess iron(II) is oxidized, and uranium(IV) is measured by titration with standardized potassium dichromate to a potentiometric end point.

In practice, this means the analyst must control the reaction order, mixing and end point detection carefully. The method is based on a weighed aliquot and a mass titration approach, which is why it is suited to accountability work where precision matters.

Sample handling and preparation

EN ISO 7097-1:2026 covers several sample types with different preparation routes: uranium metal and uranium dioxide pellets are dissolved before titration, oxide powders may be dried or ignited first, uranium hexafluoride is handled under the Annex A procedure, and uranium nitrate hexahydrate is converted to a homogeneous solution before analysis.

The document says buoyancy correction is not required for solid uranium samples under usual laboratory conditions, and it recommends replicate dissolutions for each sample. For the reader, this means sample preparation is not a single fixed step - the matrix has to be identified first, then prepared in the way that matches the material form and quality assurance plan.

Reagents, stability and equipment

EN ISO 7097-1:2026 relies on analytical-grade reagents and ISO 3696 grade 2 water. It also gives preparation and handling guidance for hydrofluoric acid, nitric acid, orthophosphoric acid, sulfuric acid, iron(II) sulfate, sulfamic acid, the oxidizing reagent, vanadium(IV) oxide sulfate and potassium dichromate titrant.

Several solutions are noted as unstable and must be checked regularly or prepared fresh, which matters in routine laboratory work because reagent drift can affect the assay. The apparatus list includes a high-impedance milli-voltmeter, a platinum electrode, a reference electrode, a balance with 0.1 mg readability, a mass titration device, stirring equipment and sampling devices for UF6.

Titration conditions and interferences

EN ISO 7097-1:2026 gives a detailed titration sequence: add the acids and reducers in the stated order, wait after the oxidation step, introduce vanadium(IV), then titrate quickly to the potentiometric end point. It also limits the aliquot size and says the titration should be completed promptly after the vanadium(IV) addition to avoid oxidation errors.

The interferences section is a major practical feature. The method is described as less sensitive to foreign ions than many uranium methods, but the user still has to consider matrix effects, impurity levels, temperature, radiation effects and the possibility of air oxidation during the timed part of the procedure. That makes this standard useful, but not “hands off” - it still requires a matrix check before use on an unfamiliar sample.

Calculation and reporting

EN ISO 7097-1:2026 gives a manual calculation route based on linear interpolation of the titration curve, plus a calculation for uranium content using the titrant concentration and the average atomic mass of uranium from isotopic composition. Annex B provides separate result expressions for uranium metal or oxide, uranium hexafluoride and uranium nitrate hexahydrate.

The document also states performance information: repeatability for pure uranium materials, bias for pure uranium solutions and irradiated fuel solutions, and a combined standard uncertainty estimate for safeguards-style work. The test report has to identify the sample, cite the document, state the method used, note any drying of oxide powders, list the results, and record unusual features or any optional or out-of-scope operations.

What terms does EN ISO 7097-1:2026 define?

EN ISO 7097-1:2026 applies the terms and definitions from ISO 5725-1, so its measurement language follows that vocabulary. The most important terms for users are:

• Aliquot - the weighed portion of the test solution that is taken for titration.
• Test solution - the solution prepared from the sample and carried into the analytical procedure.
• Mass titration - titration carried out by weighing the delivered titrant instead of reading volume.
• Potentiometric end point - the point in the titration found from the electrode potential change.
• Reference material - a certified material used to verify the potassium dichromate titrant concentration.
• Repeatability - closeness of agreement between results under the same operating conditions.
• Bias - the systematic difference between the measured result and the expected value.
• UF6 - uranium hexafluoride, one of the sample forms covered by the method and Annex A.

Who uses EN ISO 7097-1:2026?

EN ISO 7097-1:2026 is used by nuclear analytical laboratories, safeguards and accountability laboratories, fuel fabrication and reprocessing laboratories, and quality control teams working with uranium-bearing materials. It is relevant to analysts who prepare samples, calibrate titrants, run potentiometric titrations and report uranium results for pure products, reactor fuels and product solutions.

It also matters to quality managers and buyers who need a method with a stated measurement principle, sample handling route and reporting format. The document is especially relevant where routine work may benefit from automation in critical steps.

What changed in EN ISO 7097-1:2026 from the previous edition?

EN ISO 7097-1:2026 cancels and replaces ISO 7097-1:2004, and the foreword states that it is a technical revision. The changes named in the document are:

• reduced aliquot size
• updated information on interferences
• updated requirements for standardization of the potassium dichromate titrant
• the former Annex A was split into two annexes

Which standards are used with EN ISO 7097-1:2026?

EN ISO 7097-1:2026 cites these related standards and parts:

• ISO 3696 - specifies the water quality used for analytical laboratory work.
• ISO 5725-1 - provides the general principles and definitions for accuracy, trueness and precision, and its terms apply in Clause 3.
• ISO 9894 - supports subsampling of uranium hexafluoride in the liquid phase, which is needed for Annex A.
• ISO 10980 - is referenced for validation of the strength of reference solutions used to measure concentrations.
• ISO 7097-2 - the other part of the series, which the introduction says uses a cerium(IV) titration instead of potassium dichromate.

What does the EN ISO 7097-1:2026 document contain?

EN ISO 7097-1:2026 contains the method structure, the reaction scheme, the interference discussion, the reagent preparation instructions, the apparatus list, the sample preparation routes and the step-by-step titration procedure. It also includes a calculation table for interpolation, formulas for uranium content and average atomic mass, and separate result expressions for different sample types in Annex B.

Annex A gives a full uranium hexafluoride sampling and hydrolysis workflow, including cryogenic handling, transfer, dissolution and final preparation of the aliquot for analysis. Annex B provides the way to convert the titration result into mass percent for uranium metal or oxide, uranium hexafluoride and uranium nitrate hexahydrate, which is the part most laboratories will use when they need a reportable sample assay.

SLOVENSKI STANDARD
01-oktober-2026
Tehnologija jedrskega goriva - Določanje urana v raztopinah, uranovem
heksafluoridu in trdnih snoveh - 1. del: Titrimetrična metoda z redukcijo železa
(II)/oksidacijo s kalijevim dikromatom (ISO 7097-1:2025)
Nuclear fuel technology - Determination of uranium in solutions, uranium hexafluoride
and solids - Part 1: Iron(II) reduction/potassium dichromate oxidation titrimetric method
(ISO 7097-1:2025)
Kernbrennstofftechnologie - Bestimmung von Uran in Lösungen, Uranhexafluorid und
Feststoffen - Teil 1: Reduktion mit Eisen(II)/Oxidation mit
Kaliumdichromat/Titrationsverfahren (ISO 7097-1:2025)
Technologie du combustible nucléaire - Dosage de l'uranium dans des solutions,
l'hexafluorure d'uranium et des solides - Partie 1: Méthode titrimétrique par réduction au
fer(II) et oxydation au bichromate de potassium (ISO 7097-1:2025)
Ta slovenski standard je istoveten z: EN ISO 7097-1:2026
ICS:
27.120.30 Cepljivi materiali in jedrska Fissile materials and nuclear
gorivna tehnologija fuel technology
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 7097-1
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2026
EUROPÄISCHE NORM
ICS 27.120.30
English Version
Nuclear fuel technology - Determination of uranium in
solutions, uranium hexafluoride and solids - Part 1:
Iron(II) reduction/potassium dichromate oxidation
titrimetric method (ISO 7097-1:2025)
Technologie du combustible nucléaire - Dosage de Kernbrennstofftechnologie - Bestimmung von Uran in
l'uranium dans des solutions, l'hexafluorure d'uranium Lösungen, Uranhexafluorid und Feststoffen - Teil 1:
et des solides - Partie 1: Méthode titrimétrique par Reduktion mit Eisen(II)/Oxidation mit
réduction au fer(II) et oxydation au bichromate de Kaliumdichromat/Titrationsverfahren (ISO 7097-
potassium (ISO 7097-1:2025) 1:2025)
This European Standard was approved by CEN on 10 August 2026.

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. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists 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.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

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. EN ISO 7097-1:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 7097-1:2025 has been prepared by Technical Committee ISO/TC 85 "Nuclear energy,
nuclear technologies, and radiological protection” of the International Organization for Standardization
(ISO) and has been taken over as EN ISO 7097-1:2026 by Technical Committee CEN/TC 430 “Nuclear
energy, nuclear technologies, and radiological protection” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2027, and conflicting national standards
shall be withdrawn at the latest by February 2027.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: 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 the
United Kingdom.
Endorsement notice
The text of ISO 7097-1:2025 has been approved by CEN as EN ISO 7097-1:2026 without any
modification.
International
Standard
ISO 7097-1
Second edition
Nuclear fuel technology —
2025-07
Determination of uranium in
solutions, uranium hexafluoride
and solids —
Part 1:
Iron(II) reduction/potassium
dichromate oxidation
titrimetric method
Technologie du combustible nucléaire — Dosage de l'uranium
dans des solutions, l'hexafluorure d'uranium et des solides —
Partie 1: Méthode titrimétrique par réduction au fer(II) et
oxydation au bichromate de potassium
Reference number
ISO 7097-1:2025(en) © ISO 2025

ISO 7097-1:2025(en)
© ISO 2025
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
ISO 7097-1:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reactions and interferences . 2
5.1 Reactions .2
5.2 Interferences .2
6 Reagents . 3
7 Apparatus . 6
8 Sample preparation . 7
8.1 General .7
8.2 Uranium metal .7
8.3 Uranium dioxide pellets .7
8.4 Uranium oxide powder (UO , UO , U O ) .7
2 3 3 8
8.5 Uranium hexafluoride .8
8.6 Uranium nitrate hexahydrate .8
9 Procedure . 8
10 Expression of the results . 9
10.1 General .9
10.2 Method of calculation .9
10.2.1 Linear interpolation .9
10.2.2 Calculation for the test solution .10
10.2.3 Calculations for samples .10
10.2.4 Average atomic mass .10
10.3 Repeatability .11
10.4 Bias .11
11 Test report .11
Annex A (normative) Uranium hexafluoride sampling and preparation of the test solution .12
Annex B (informative) Expression of results for samples . 14
Bibliography .15

iii
ISO 7097-1:2025(en)
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 through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and 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 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 5, Nuclear installations, processes and technologies.
This second edition cancels and replaces the first edition (ISO 7097-1:2004), which has been technically
revised.
The main changes are as follows:
— aliquot size has been reduced (see Clause 4);
— information on interferences has been updated (see 5.2);
— requirements for standardisation of potassium dichromate titrant were updated (see 6.16);
— previous Annex A was divided into two annexes (Annex A and Annex B).
A list of all parts in the ISO 7097 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
ISO 7097-1:2025(en)
Introduction
The ISO 7097 series documents describe two independent procedures for the determination of uranium in
solutions, uranium hexafluoride and solids. The two procedures are similar: this document uses a titration
with potassium dichromate while ISO 7097-2 uses a titration with cerium(IV).

v
International Standard ISO 7097-1:2025(en)
Nuclear fuel technology — Determination of uranium in
solutions, uranium hexafluoride and solids —
Part 1:
Iron(II) reduction/potassium dichromate oxidation
titrimetric method
1 Scope
This document describes an analytical method for the determination of uranium in samples from pure
product materials such as U metal, UO , UO , uranyl nitrate hexahydrate, uranium hexafluoride and U O
2 3 3 8
from the nuclear fuel cycle. This procedure is sufficiently accurate and precise to be used for nuclear
materials accountability. This method can be used directly for the analysis of most uranium and uranium
oxide nuclear reactor fuels, either irradiated or un-irradiated, and of uranium nitrate product solutions.
Fission products equivalent to up to 10 % burn-up of heavy atoms do not interfere, and other elements which
could cause interference are not normally present in sufficient quantity to affect the result significantly.
The method recommends that an aliquot of sample is weighed and that a mass titration is used, in order
to obtain improved precision and accuracy. This does not preclude the use of alternative techniques which
could give equivalent performance. The use of automatic device(s) in the performance of some critical steps
of the method has some advantages, mainly in the case of routine analysis.
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 3696, Water for analytical laboratory use — Specification and test methods
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles
and definitions
ISO 9894, Subsampling of uranium hexafluoride in the liquid phase
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5725-1 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/
4 Principle
Uranium(VI) is reduced to uranium(IV) in concentrated phosphoric acid reagent, in the presence of sulfamic
acid, by reaction with iron(II) sulfate. The excess of iron(II) sulfate is subsequently oxidized by nitric acid
in the presence of molybdenum, and the uranium(IV) is determined by mass titration with standardized
[2][3][4][5]
potassium dichromate solution to a potentiometric end point .

ISO 7097-1:2025(en)
An aliquot of the sample containing about 15 mg to 50 mg of uranium solution is taken for the titration. An
excess of iron(II) sulfate solution is then added to reduce all the uranium to the quadrivalent state. Sulfamic
acid is added to eliminate nitrite ions present at this stage. The excess of iron(II) is oxidized by nitric acid,
catalysed by molybdenum. The uranium is determined by mass titration with standardized potassium
dichromate solution to a potentiometric end point. To improve precision, the titration is performed in the
presence of vanadium in dilute sulfuric acid, which increases the kinetics of the reaction. The addition of
vanadium(IV) solution acts to dilute the sample solution and shift the redox potential so as to allow the
titration to proceed.
The potassium dichromate solution is calibrated using an internationally recognized reference material,
such as SRM 136e (or equivalent) from the U.S. National Institute of Standards and Technology (NIST), or
[1]
one that is verified as described in 6.15; see ISO 10980 .
5 Reactions and interferences
5.1 Reactions
Under the given experimental conditions, the principal reactions are as follows:
a) In concentrated phosphoric acid solution:
2+
2+ + 4+ 3+
UO + 2Fe + 4H → U + 2Fe + 2H O
2 2
Mo
−
2+ + 3+
3Fe + NO + 4H → 3Fe + NO + 2H O
3 2
Mo
−
2+ + 3+
Fe + NO + 2H → Fe + NO + H O
2 2
Mo
− −
2+ + 3+
2Fe + NO + 2H → 2Fe + NO + H O
3 2 2
b) In diluted phosphoric acid solution:
2+
4+ 3+ 2+ +
U + 2Fe + 2H O → UO + 2Fe + 4H
2 2
2+ 2+ + 3+ 3+
Fe + VO + 2H → Fe + V + H O
The overall reaction can be represented as follows:
2+
4+ 2+ 3+
U + 2VO → UO + 2V
c) On titration with potassium dichromate solution:
2−
3+ + 3+ 2+
Cr O + 6V + 2H → 2Cr + 6VO + H O
27 2
4+
which is equivalent to the titration of U with dichromate:
2− 2+
4+ + 3+
Cr O + 3U + 2H → 2Cr + 3UO + H O
27 2 2
5.2 Interferences
This procedure is less subject to interference from foreign ions than most other methods of determining
[6]
uranium . In usual reprocessing solutions, fluoride, perchlorate, sulfate, Be, Si, Nb, Ti, Cr, Fe, Co, Ni, W,
Cu, Sb(V), Pb, Pu, Am, the rare earths and the alkaline earth metals do not interfere. The extent of Np

ISO 7097-1:2025(en)
interference, if any, has not been verified. Titration shall be completed within five minutes of sample dilution
with vanadyl solution to avoid negative assay errors due to air oxidation.
For titrations involving uranium aliquots in the range of 15 mg to 50 mg:
−
a) Al, Zr, and NO do not interfere when present in the range 0 mg to 4 mg in the aliquot.
b) As(V) and Th do not interfere when present in the range 0 mg to 1 mg in the aliquot.
c) Mo and Mn do not interfere when present in the range 0 mg to 0,5 mg in the aliquot; Mo interferes only if
large amounts of nitrate are also present and vice versa.
d) Bromide, oxalate, Au, Sn, and some platinum group elements interfere at 0,1 % when present at levels of
2 mg in the aliquot.
e) Interference from iodine, iodate, Ag, V(V), and Tc is more severe. Each of these impurity levels shall be
kept below 1 mg in the aliquot (0,1 % interference at 1 mg level).
f) As(III) and Sb(III) yield a bias proportional to the amount present. When present at 0,5 mg levels in the
aliquot, As(III) can cause a positive bias of 0,3 % and Sb(III) can cause a bias of ~4 %.
g) Nitrate and peroxide will not interfere unless present at high concentrations as described here. Nitrate
levels shall be <3 ml of concentrated nitric acid. Excessive amounts of peroxide is indicated by failure to
observe dark coloration during the oxidation step. Thus, it is likely that the titration results of a sample
containing excessive amounts of peroxide would be biased.
h) A temperature range of 20 °C to 24 °C and at a fixed temperature will have no influence on the titration
[6][7]
results. Temperatures outside of this range can affect reaction rates and times .
The possible effect of intense β and γ radiation and of some radioactive species (for example ruthenium)
on the electrode system remains to be established. Effects on the electrode by intense radiation have been
observed during a single run. Since the types of material to be analysed cover a very wide range, the user
of the method should consider the possibility of interference for each specific case, considering published
information and the results of any additional experiments which might be necessary.
6 Reagents
Use only reagents of recognized analytical grade, and only water as specified in 6.1.
6.1 Water, meeting the requirements for ISO 3696 grade 2 water (electrical conductivity less than
0,1 mS/m and resistivity greater than 0,01 MΩ⋅m at 25 °C).
It is recommended that the water used be obtained from a water purification system that delivers ultrapure
water having a resistivity greater than 0,18 MΩ⋅m (usually expressed by manufacturers of water purification
systems as 18 MΩ⋅cm).
6.2 Hydrofluoric acid (HF), c ≈ 29 mol/l ≈ 48 % w/w ( d = 1,18).
WARNING — Hydrofluoric acid is a highly corrosive and toxic acid that can severely burn skin, eyes,
and mucous membranes. The burning sensation is not immediately apparent and might not be felt for
several hours. The fluoride ion readily penetrates the skin, even with dilute concentrations, causing
destruction of deep tissue layers. Unlike other acids that are rapidly neutralized, hydrofluoric acid
reactions with tissue can continue for days if left untreated. Familiarization and conformity with the
safety data sheet is essential.
6.3 Nitric acid (HNO ), c ≈ 16 mol/l ≈ 69 % w/w ( d = 1,42).
3 4
ISO 7097-1:2025(en)
6.4 Nitric acid (HNO ), c ≈ 8 mol/l.
Dilute the 16 mol/l nitric acid (6.3) 2 to 1 with distilled water.
6.5 Nitric acid (HNO ), c ≈ 4 mol/l.
Dilute the 16 mol/l nitric acid (6.3) 4 to 1 with distilled water.
6.6 Orthophosphoric acid (H PO ), c ≈ 15 mol/l ≈ 85 % w/w ( d =17, 1 ).
3 4 4
Historically, issues relating to the presence of excessive amounts of reducing agents such as Sb(III) had
been reported for this reagent. The use of analytical grade reagents is, in general, a sufficient precautionary
measure to avoid these issues.
6.7 Phosphoric acid reagent. Add a few drops of 4 % potassium dichromate solution (6.14) to a 2,5 l
reagent bottle of orthophosphoric acid and mix.
A pale straw colour is expected. If the solution turns green, it has been contaminated with reducing agents
and should be discarded.
6.8 Sulfuric acid (H SO ), c ≈ 18 mol/l ≈ 96 % in mass fraction ( d =18, 4 ).
2 4 4
6.9 Sulfuric acid (H SO ), c ≈ 1,0 mol/l.
2 4
Add 56 ml of sulfuric acid (6.8) slowly and carefully to 900 ml of water (6.1), while stirring. Allow to cool and
adjust the solution to 1 000 ml with water (6.1).
6.10 Iron(II) sulfate (FeSO ·7H O), c ≈ 1 mol/l.
4 2
Add 10 ml of concentrated sulfuric acid (6.8) carefully to 75 ml of water (6.1) in a 500 ml beaker with
constant stirring. Add 28 g ± 1 g of iron(II) sulfate (FeSO ·7H O) and stir until it is dissolved. Dilute to 100 ml
4 2
with water (6.1) and mix. This solution is not stable under all conditions for extended periods of time and its
use shall be verified on a regular basis determined by laboratory experience using an appropriate quality
control test or be prepared fresh once a week.
6.11 Sulfamic acid(NH SO H),c ≈ 1,55 mol/l.
2 3
Dissolve 150 g of sulfamic acid in less than 1 l of water (6.1) at room temperature and dilute final solution
to 1 l. Filter freshly prepared sulfamic acid through a suitable filter paper before storing in glass or low-
density polyethylene (LDPE) bottle. As this solution is almost saturated, heating would tend to decompose
the sulfamic acid. This solution is not stable, and its use shall be verified, as appropriate, on a regular basis
using an appropriate quali
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