ISO 9681:2026

• Abstract:

  This document specifies a flame atomic absorption spectrometric method for the determination of iron content in manganese ores and concentrates. This document is applicable to iron content from 0,20 % (mass fraction) to 10,00 % (mass fraction), inclusive.

• Status: Published
• Publication Date: 12-Nov-2026
• ICS: 73.060.20 - Manganese ores
• Technical Committee: ISO/TC 132 - Ferroalloys
• Drafting Committee: ISO/TC 132 - Ferroalloys
• Current Stage: 6060 - International Standard published
• Start Date: 13-Nov-2026
• Completion Date: 13-Nov-2026

• Revises: ISO 9681:1990 - Manganese ores and concentrates — Determination of iron content — Flame atomic absorption spectrometric method
• Effective Date: 18-May-2024

ISO 9681 is an ISO standard for determining iron content in manganese ores and concentrates by flame atomic absorption spectrometric method. It specifies two decomposition routes, calibration, calculation, and reporting for products with iron content from 0.20 % to 10.00 % by mass. It is written for laboratories that test manganese ores and concentrates and should be read with ISO 4297.

What does ISO 9681 specify?

ISO 9681 specifies a flame atomic absorption spectrometric method for measuring iron in manganese ores and concentrates. The document is organized into scope, normative references, terms and definitions, principle, reagents, apparatus, sampling and samples, procedures, expression of results, and test report, with two annexes covering supporting information and result acceptance.

Annex	What it covers
Annex A	Additional information on the international interlaboratory test
Annex B	Flow chart for the acceptance procedure of test results

The scope limits the method to iron contents between 0.20 % and 10.00 % mass fraction. The document also points users to ISO 4297 for dry-basis treatment, so the reported result matches the way the sample condition is handled in the broader manganese ore analysis system.

What are the key requirements of ISO 9681?

ISO 9681 requires the analyst to choose one of two decomposition routes, prepare calibration solutions matched to the expected iron level, measure absorbance in an air-acetylene flame, and report the result after applying the specified calculation and result-checking steps. These steps matter because the method depends on matching the sample chemistry, matrix background, and instrument range to the iron level being measured.

Sample preparation and blank control

ISO 9681 requires a laboratory sample of minus 100 μm particle size prepared according to ISO 4296-1 and ISO 4296-2. The test portion is 0.5 g of air-dried sample or sample dried at 105 °C to 110 °C, and at least two measurements are carried out for the same dry sample. A blank test uses 0.25 g of metallic manganese through all stages, which helps separate the sample signal from reagent and procedural contributions.

Two decomposition methods

ISO 9681 gives Method 1 and Method 2. Method 1 uses hydrochloric, perchloric and hydrofluoric acids, followed by fusion of the insoluble residue. Method 2 uses hydrochloric, nitric and perchloric acids, then removes silica with sulfuric and hydrofluoric acids before the same fusion step. In practice, the analyst selects the route that fits the sample matrix and follows the residue treatment exactly, because the dissolved residue is part of the final test solution.

Calibration and measurement conditions

ISO 9681 requires background solution A for ores with CaO content below 5 % and background solution B when CaO is above 5 %. The calibration set is prepared in seven flasks, with one set for lower iron levels and another for higher iron levels. Measurements are made at 248.3 nm for the lower range, and at 248.3 nm or 344.06 nm for higher iron levels, after verifying instrument sensitivity, linearity, and stability.

Calculation, precision, and reporting

ISO 9681 calculates iron content from the concentration read from the calibration graph, the test portion mass, the final solution volume, and the dry-basis conversion factor. The document also gives expressions for repeatability and reproducibility, a procedure for comparing duplicate results, and a trueness check using a certified reference material or reference material. The test report must identify the laboratory, the sample, the result, and any unusual observations or extra operations that may have affected the result.

What terms does ISO 9681 define?

ISO 9681 does not list formal terms and definitions, but it uses several technical terms that are central to the method.

• AAS - Atomic absorption spectrometry, the measurement technique used here to read iron absorbance in an air-acetylene flame.
• CRM - Certified reference material, used to check trueness against a certified value.
• RM - Reference material, used with a known reference value when checking trueness.
• CaO - Calcium oxide content, used to decide whether background solution A or B is added.
• Repeatability limit, r - The limit used to judge whether duplicate analytical values from the same laboratory agree closely enough.
• Reproducibility limit, R - The limit used to judge agreement between final results reported by different laboratories.

Who uses ISO 9681?

ISO 9681 is used by testing laboratories, quality control staff, and technical buyers who need a standard way to determine iron in manganese ores and concentrates. It is relevant in mining, minerals processing, and chemical analysis laboratories that prepare samples, run atomic absorption measurements, and compare results across laboratories.

It is also useful for laboratories that issue formal test reports or verify method performance with reference materials. The interlaboratory precision data in Annex A support users who need to understand how the method performed in collaborative testing.

What changed in ISO 9681 from the previous edition?

ISO 9681 is the second edition and it replaces ISO 9681:1990. The document states that it was technically revised.

The stated changes include updated concentrations for the iron standard solution and calibration solution, removal of a reference instrument parameter setting value, changed test portion and blank experiment masses, added residue treatment in the decomposition step, more detailed washing and heating steps, a revised general treatment of results, and the addition of Clause 10, Annex A, and Annex B.

Which standards are used with ISO 9681?

ISO 9681 refers to several companion standards that support sampling, glassware, water quality, and result evaluation.

• ISO 310 - moisture determination for analytical samples, used for air-dried samples and dry-basis correction.
• ISO 648 - class A single-volume pipettes, used for accurate solution handling.
• ISO 1042 - class A one-mark volumetric flasks, used for preparing fixed-volume solutions.
• ISO 3696 - grade 3 water for analytical laboratory use.
• ISO 4296-1 - increment sampling of manganese ores.
• ISO 4296-2 - preparation of manganese ore samples.
• ISO 4297 - general instructions for chemical analysis of manganese ores and concentrates.
• ISO 5725-2 - statistical treatment of precision data.
• ISO Guide 33405 - characterization and assessment of homogeneity and stability of reference materials.

What does the ISO 9681 document contain?

ISO 9681 contains the full analytical workflow: sample preparation, reagent recipes, apparatus requirements, two decomposition procedures, calibration tables, measurement instructions, result calculations, precision formulas, and a test report checklist. It also includes a normative flow chart for accepting test results, which helps laboratories decide whether duplicate values can be combined into a final result.

Annex A gives interlaboratory test information, including sample set details, cooperative-test results, and precision evaluation. Annex B provides the decision flow for accepting analytical values, which is the practical step used before reporting the final iron content.

International
Standard
ISO 9681
Second edition
Manganese ores and
2026-11
concentrates — Determination
of iron content — Flame atomic
absorption spectrometric method
Minerais et concentrés de manganèse — Dosage du fer —
Méthode par spectrométrie d'absorption atomique dans la
flamme
Reference number
© ISO 2026
All rights reserved.
This ISO publication is protected by copyright and is owned by ISO and/or its licensors.
The content of this ISO publication is provided under licence, not sold. Use is subject to the applicable licence terms issued by ISO,
an ISO member body, or an authorized third-party distributor.
Except as required for implementation or expressly permitted by a separate licence, no part of this ISO publication may be
reproduced, distributed, modified, used, or made available in any form or by any means – electronic or mechanical, including
photocopying, scanning, recording, or posting on internal or external digital platforms.
Any use beyond the scope of the granted rights is prohibited and may result in legal action.
ISO copyright office
CP 401 • CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 3
7 Sampling and samples . . 3
8 Procedures . 3
8.1 Test portion .3
8.2 Blank test .3
8.3 Determination .4
8.3.1 Decomposition of the test portion .4
8.3.2 Preparation of the test solution .4
8.4 Preparation of the set of calibration solutions .5
8.4.1 Iron content greater than 0,20 % (mass fraction) .5
8.4.2 Iron content greater than 2,50 % (mass fraction) .5
8.5 Calibration and measurements . .5
8.5.1 Spectrometric measurements .5
8.5.2 Plotting the calibration graph .6
9 Expression of results . 6
9.1 Calculation .6
9.2 General treatment of results .6
9.2.1 Expression of precision .6
9.2.2 Determination of analytical result .7
9.2.3 Interlaboratory precision .7
9.2.4 Check for trueness .7
9.2.5 Calculation of the final result .8
10 Test report . 8
Annex A (informative) Additional information on the international interlaboratory test . 9
Annex B (normative) Flow chart for the acceptance procedure of test results .13
Bibliography . 14

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 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 document 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 132, Ferroalloys.
This second edition cancels and replaces the first edition (ISO 9681:1990), which has been technically
revised.
The main changes are as follows:
— in 5.15 and 5.16 (previously in 4.13), the concentration of the iron standard solution has been changed;
— in 6.5 (previously in 5.3), the reference value of instrument parameters setting has been deleted;
— in 8.1 (previously in 7.1), the mass of the sample has been changed, and the requirement of parallel
measurement times has been increased;
— in 8.2 (previously in 7.2), the mass of manganese in the blank experiment has been changed;
— in 8.3, the residue treatment has been included in the sample decomposition step, and 7.3.1 and 7.3.2
have been combined into 8.3.1;
— in 8.3.1 (previously in 7.3.1 and 7.3.2), the times of washing beaker and filter paper with hot hydrochloric
acid have been specified, the steps for heating and drying filter paper and residue on electric furnace
have been added, the time range of the residue melting and the volume of the beaker have been defined,
and the amount of hydrochloric acid used has been changed;
— in 8.4 (previously in 7.4), the concentration of the calibration solution has been changed;
— in 9.2 (previously in 8.2), the paragraph of the “permissible tolerances on results of parallel
determinations” has been replaced with the “general treatment of results”;
— in Clause 10, the test report has been added;
— Annex A “Additional information on the international interlaboratory test” has been added;
— Annex B “Flow chart for the acceptance procedure of test results” has been added.

iv
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.

v
International Standard ISO 9681:2026(en)
Manganese ores and concentrates — Determination of iron
content — Flame atomic absorption spectrometric method
1 Scope
This document specifies a flame atomic absorption spectrometric method for the determination of iron
content in manganese ores and concentrates.
This document is applicable to iron content from 0,20 % (mass fraction) to 10,00 % (mass fraction), inclusive.
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 310, Manganese ores and concentrates — Determination of hygroscopic moisture content in analytical
samples — Gravimetric method
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4296-1, Manganese ores — Sampling — Part 1: Increment sampling
ISO 4296-2, Manganese ores — Sampling — Part 2: Preparation of samples
ISO 4297, Manganese ores and concentrates — Methods of chemical analysis — General instructions
3 Terms and definitions
No terms and definitions are listed in this document.
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
Method 1: Decompose the test portion by treating with hydrochloric, perchloric and hydrofluoric acids.
Separate the insoluble residue, fuse the residue with a fusion mixture, and dissolve the cooled melt in the
test solution. Aspirate the test solution into an air-acetylene flame in an atomic absorption spectrometer
and measure the absorbance at a wavelength of 248,3 nm or 344,06 nm.
Method 2: Decompose the test portion by treatment with hydrochloric, nitric and perchloric acids and filter
the insoluble residue. Remove silica by volatilization with sulfuric and hydrofluoric acids, fuse the residue
with a fusion mixture, and dissolve the cooled melt in the test solution. Aspirate the test solution into an
air-acetylene flame in an atomic absorption spectrometer and measure the absorbance at a wavelength of
248,3 nm or 344,06 nm.
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
grade 3 water as specified in ISO 3696.
5.1 Metallic manganese, 99,9 % purity.
5.2 Calcium carbonate.
5.3 Iron, 99,99 % purity.
5.4 Hydrochloric acid, ρ 1,19 g/ml.
5.5 Hydrochloric acid, ρ 1,19 g/ml, diluted 1+50.
5.6 Hydrofluoric acid, ρ 1,14 g/ml.
5.7 Perchloric acid, ρ 1,61 g/ml.
5.8 Nitric acid, ρ 1,41 g/ml.
5.9 Nitric acid, ρ 1,41 g/ml, diluted 1+1.
5.10 Sulfuric acid, ρ 1,84 g/ml, diluted 1+1.
Slowly and with great care, pour 1 volume of concentrated sulfuric acid into an equal volume of water.
5.11 Hydrogen peroxide, 30 % (mass fraction) solution.
5.12 Fusion mixture.
Mix anhydrous sodium carbonate and anhydrous sodium tetraborate, in the proportion 3+1.
5.13 Background solution A, for ores having CaO content less than 5 % (mass fraction).
Dissolve 5 g of metallic manganese (5.1) in 40 ml of nitric acid (5.9). Add 30 ml of perchloric acid (5.7). Heat
until fumes of perchloric acid appear. Cool the solution and dilute with water. Add 7,5 g of anhydrous sodium
carbonate, 2,5 g of anhydrous sodium tetraborate and 30 ml of hydrochloric acid (5.4). After dissolution,
transfer the two solutions to a 500 ml one-mark volumetric flask, dilute to the mark with water and mix.
5.14 Background solution B, for ores having CaO content greater than 5 % (mass fraction).
Dissolve 4 g of metallic manganese (5.1) and 1,8 g of calcium carbonate (5.2) in 40 ml of nitric acid (5.9) and
proceed as in 5.13.
5.15 Iron standard solution A, 2 000 μg/ml.
Dissolve 2,000 g of iron (5.3) in 40 ml of nitric acid (5.8). Add 40 ml of perchloric acid (5.7) and evaporate
until fumes of perchloric acid appear and last for 4 min to 5 min. Cool the solution and dilute with water.
Transfer the solution to a 1 000 ml one-mark volumetric flask, dilute to the mark with water and mix.
5.16 Iron standard solution B, 200 μg/ml.
Transfer 20 ml of iron standard solution A (5.15) to a 200 ml one-mark volumetric flask, dilute to the mark
with water and mix.
6 Apparatus
The usual laboratory apparatus and, in particular, the following shall be used.
All laboratory glassware shall be class A, in accordance with ISO 648 or ISO 1042 as appropriate.
6.1 Platinum crucible.
6.2 Polytetrafluoroethylene (PTFE) beaker.
6.3 Analytical balance, sensitivity 0,1 mg.
6.4 High temperature furnace, maximum temperature up to 1 100 °C.
6.5 Atomic absorption spectrometer, equipped with an air-acetylene burner and iron hollow cathode
lamp.
The atomic absorption spectrometer used is satisfactory if it meets the following criteria:
a) Minimum sensitivity: The absorbance of the calibration solution of highest iron content (see 8.4) shall
be at least 0,25.
b) Curve linearity: The slope of the calibration graph covering the top 20 % of the concentration range
(expressed as a change in absorbance) shall be not less than 0,7 of the value of the slope for the bottom
20 % of the concentration range determined in the same way.
c) Minimum stability: The standard deviation of the absorbance of the calibration solution of highest
concentration and the standard deviation of the absorbance of the zero-calibration solution, each being
calculated from a sufficient number of repetitive measurements, shall be less than 1,5 % and 0,5 %
respectively of the mean value of the absorbance of the calibration solution of highest concentration.
The use of either a strip chart recorder or a digital readout device should be used to evaluate the criteria and
for all subsequent measurements.
Instrument parameters can vary with each instrument. Set the instrument parameters according to the
instrument model.
7 Sampling and samples
For analysis, use a laboratory sample of minus 100 μm particle size which has been taken in accordance with
ISO 4296-1 and prepared in accordance with ISO 4296-2.
8 Procedures
8.1 Test portion
Weigh 0,5 g of an air-dried sample or the sample dried at 105 °C to 110 °C, accurate to 0,1 mg. The air-drying
test material shall be analysed for moisture retention in accordance with ISO 310.
For the same dry sample, at least two measurements shall be carried out simultaneously.
When using the sample dried at 105 °C
...