|
International
Standard
ISO 4941
Third edition
Steel and iron — Determination of
2024-07
molybdenum content — Thiocyanate
spectrophotometric method
Aciers et fontes — Détermination des teneurs en molybdène —
Méthode spectrophotométrique au thiocyanate
Reference number
© ISO 2024
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: +41 22 749 01 11
Email: [email protected]
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 preparation of the test samples . 3
8 Procedure . 3
8.1 Test portion .4
8.2 Determination .4
8.2.1 Preparation of the test solution .4
8.2.2 Preparation of the compensating solution .4
8.2.3 Formation and extraction of the coloured complex .4
8.2.4 Spectrophotometric measurements .5
8.3 Establishment of the calibration curve .5
8.3.1 Preparation of the calibration solutions, related to spectrophotometric
measurements performed using cells with an optical path length of 10 mm .5
8.3.2 Spectrophotometric measurements .5
8.3.3 Plotting the calibration curve .6
9 Expression of results . 6
9.1 Method of calculation .6
9.2 Precision . . .7
10 Test report . 7
Annex A (informative) Additional information on the international interlaboratory test . 8
Annex B (informative) Graphical representation of precision data .10
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 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 17, Steel, Subcommittee SC 1, Methods of
determination of chemical composition.
This third edition cancels and replaces the second edition (ISO 4941:1994), which has been technically
revised.
The main changes are as follows:
— the normative references have been revised;
— the precision data has been updated.
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
International Standard ISO 4941:2024(en)
Steel and iron — Determination of molybdenum content —
Thiocyanate spectrophotometric method
1 Scope
This document specifies a thiocyanate spectrophotometric method for the determination of molybdenum
contents in steel and iron. The method is applicable to molybdenum mass fractions between 0,005 % and
0,125 %.
Vanadium and tungsten interfere with the measurement if, because of their contents, the V/Mo ratio is
greater than 16 or the W/Mo ratio is greater than 8.
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 385, Laboratory glassware — Burettes
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 4800, Laboratory glassware — Separating funnels and dropping funnels
ISO 14284, Steel and iron — Sampling and preparation of samples for the determination of chemical composition
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological 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
Dissolution of a test portion in an appropriate mixture of acids and decomposition of the carbides by
oxidation.
Quantitative formation of a coloured complex of molybdenum, in the presence of thiocyanate, iron(II) and/
or copper(II) ions and extraction of this compound using butyl acetate.
Spectrophotometric measurement of the coloured complex at a wavelength of about 470 nm.
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and grade 2
water as specified in ISO 3696.
5.1 Pure iron, in flake or powder form, with a molybdenum content less than 0,000 5 % (mass fraction)
and free from tungsten and vanadium.
5.2 Butyl acetate.
5.3 Nitric acid, ρ approximately 1,40 g/ml.
5.4 Hydrochloric acid, ρ approximately 1,19 g/ml.
5.5 Hydrochloric acid, ρ approximately 1,19 g/ml, diluted (3 + 1).
5.6 Hydrochloric acid, ρ approximately 1,19 g/ml, diluted (1 + 1).
5.7 Acid mixture I.
Add 2 volumes of hydrochloric acid (5.4) to 1 volume of nitric acid (5.3) and mix well. Prepare this mixture
immediately before use.
5.8 Acid mixture II.
Add 150 ml of orthophosphoric acid (ρ approximately 1,70 g/ml) to 300 ml of water, and add 360 ml of
perchloric acid (ρ approximately 1,67 g/ml) to this diluted acid (see NOTE). Transfer the solution into a
1 000 ml one-mark volumetric flask. Dilute to the mark with water and mix.
NOTE In the preparation of this acid mixture, 360 ml of perchloric acid (ρ approximately 1,67 g/ml) can be
replaced by 150 ml of sulfuric acid (ρ approximately 1,84 g/ml).
5.9 L(+)- ascorbic acid solution, 100 g/l.
Prepare this solution just before use.
5.10 Ammonium thiocyanate solution, 320 g/l.
Store this solution away from light.
5.11 Copper(II), solution corresponding to 70 mg of Cu(II) per litre in a hydrochloric acid medium.
Dissolve 0,188 g of copper(II) chloride di-hydrate (CuCl ·2H O) or 0,275 g of copper(II) sulfate penta-
2 2
hydrate (CuSO ·5H O) into 125 ml of hydrochloric acid (5.4). Transfer the solution into a 1 000 ml one-mark
4 2
volumetric flask, dilute to the mark with water and mix.
5.12 Tin(II) copper(II) chloride, solution in a hydrochloric acid medium.
Dissolve 80 g of tin(II) chloride di-hydrate (SnCl ·2H O) in 155 ml of hydrochloric acid (5.4). Add 100 ml
2 2
of copper(II) solution (5.11). Transfer the solution into a 1 000 ml one-mark volumetric flask, dilute to the
mark with water and mix.
Prepare this solution just before use.
5.13 Iron, 10 g/l solution
Weigh, to the nearest 0,01 g, 10,0 g of the pure iron (5.1). Place the portion into a 1 000 ml beaker, and
dissolve by careful addition of 500 ml of the acid mixture II (5.8). After cooling, transfer into a 1 000 ml one-
mark volumetric flask, dilute to the mark with water and mix.
5.14 Molybdenum, standard solutions.
5.14.1 Molybdenum standard solution, corresponding to 500 mg/l of Mo.
Weigh, to the nearest 0,1 mg, 0,500 g of molybdenum [minimum purity 99,95 % (mass fraction), see NOTE].
Transfer the portion into a 1 000 ml beaker. Add 500 ml of hydrochloric acid (5.4) and heat; add two drops of
nitric acid (5.3) to aid dissolution. Cool the solution.
Transfer the solution into a 1 000 ml one-mark volumetric flask. Dilute to the mark with water and mix.
1 ml of this standard solution contains 500 µg of Mo.
NOTE Pure metals, especially those in powder form, are subject to changes in their stoichiometry as a result of
oxidation, therefore check the oxygen content prior to use.
5.14.2 Molybdenum standard solution, corresponding to 5 mg/l of Mo.
Transfer 10,0 ml of the molybdenum standard solution (5.14.1) into a 1 000 ml, one-mark volumetric flask.
Add 500 ml of hydrochloric acid (5.4) dilute to the mark with water and mix.
Prepare this solution immediately before use.
1 ml of this standard solution contains 5 µg of Mo.
6 Apparatus
Dur
...