Solid mineral fuels -- Determination of total carbon, hydrogen and nitrogen content -- Instrumental method

ISO 29541:2010 specifies a method for the determination of total carbon, hydrogen and nitrogen in coal and coke by instrumental methods.

Combustibles minéraux solides -- Dosage du carbone, de l'hydrogène et de l'azote totaux -- Méthode instrumentale

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Publication Date
28-Sep-2010
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9060 - Close of review
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05-Jun-2021
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INTERNATIONAL ISO
STANDARD 29541
First edition
2010-10-01
Solid mineral fuels — Determination of
total carbon, hydrogen and nitrogen
content — Instrumental method
Combustibles minéraux solides — Dosage du carbone, de l'hydrogène
et de l'azote totaux — Méthode instrumentale
Reference number
ISO 29541:2010(E)
ISO 2010
---------------------- Page: 1 ----------------------
ISO 29541:2010(E)
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downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
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COPYRIGHT PROTECTED DOCUMENT
© ISO 2010

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
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Published in Switzerland
ii © ISO 2010 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 29541:2010(E)
Contents Page

Foreword ............................................................................................................................................................iv

Introduction.........................................................................................................................................................v

1 Scope......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Terms and definitions ...........................................................................................................................1

4 Principle..................................................................................................................................................2

5 Reagents.................................................................................................................................................2

6 Apparatus...............................................................................................................................................3

7 Preparation of the test sample.............................................................................................................3

8 Procedure...............................................................................................................................................3

8.1 Instrument set-up ..................................................................................................................................3

8.2 Blank analyses.......................................................................................................................................3

8.3 Conditioning and instrument stability check .....................................................................................3

8.4 Calibration..............................................................................................................................................3

8.5 Verification of calibration .....................................................................................................................4

8.6 Analysis of test samples.......................................................................................................................4

9 Expression of results............................................................................................................................4

10 Precision.................................................................................................................................................5

10.1 Repeatability limit..................................................................................................................................5

10.2 Reproducibility limit ..............................................................................................................................5

11 Test report..............................................................................................................................................6

Annex A (informative) Recommendations for calibration ..............................................................................7

Bibliography......................................................................................................................................................10

© ISO 2010 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 29541:2010(E)
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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 29541 was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee SC 5,

Methods of analysis.

This first edition of ISO 29541 cancels and replaces ISO/TS 12902:2001, which has been technically revised.

iv © ISO 2010 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 29541:2010(E)
Introduction

The reliable determination of total carbon, hydrogen and nitrogen is important for engineering calculations

applied to the combustion of coal. The precise and accurate determination of the carbon content of coal is

essential for carbon accounting purposes.
© ISO 2010 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 29541:2010(E)
Solid mineral fuels — Determination of total carbon, hydrogen
and nitrogen content — Instrumental method

WARNING — The use of this International Standard can involve hazardous materials, operations and

equipment. This International Standard does not purport to address all of the safety problems

associated with its use. It is the responsibility of the user of this International Standard to establish

appropriate safety and health practices and determine the applicability of regulatory limitations prior

to use.
1 Scope

This International Standard specifies a method for the determination of total carbon, hydrogen and nitrogen in

coal and coke by instrumental methods.

NOTE This International Standard has been validated for coal only in accordance with the principles of ISO 5725-1.

2 Normative references

The following referenced documents are indispensable for the application 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 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample

ISO 1213-2, Solid mineral fuels — Vocabulary — Part 2: Terms relating to sampling, testing and analysis

ISO 5068-2, Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric

method for moisture in the analysis sample

ISO 5069-2, Brown coals and lignites — Principles of sampling — Part 2: Sample preparation for

determination of moisture content and for general analysis

ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test sample

by drying in nitrogen

ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples

ISO 13909-6, Hard coal and coke — Mechanical sampling — Part 6: Coke — Preparation of test samples

ISO 18283, Hard coal and coke — Manual sampling
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 1213-2 apply.

© ISO 2010 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 29541:2010(E)
4 Principle

Carbon, hydrogen and nitrogen are determined concurrently in a single instrumental procedure. The

quantitative conversion of the carbon, hydrogen and nitrogen into their corresponding gases (CO , H O,

2 2

N /NO ) occurs during combustion of the sample at an elevated temperature in an atmosphere of oxygen.

2 x

Combustion products which would interfere with the subsequent gas analysis are removed. Oxides of nitrogen

(NO ) produced during the combustion are reduced to N before detection. The carbon dioxide, water vapour

x 2

and elemental nitrogen in the gas stream are then determined quantitatively by appropriate instrumental gas

analysis procedures.
5 Reagents
Unless otherwise specified, all reagents shall be of analytical reagent grade.

5.1 Carrier gas, helium or other suitable gas as specified by the instrument manufacturer.

5.2 Oxygen, as specified by the instrument manufacturer.

5.3 Additional reagents, of types and qualities specified by the instrument manufacturer.

5.4 Calibration materials: see Table 1.

Table 1 — Examples of suitable calibration materials and their stoichiometric contents of C, H and N

Mass fraction
Name Formula
Carbon Hydrogen Nitrogen
EDTA
C H N O
41,1 5,5 9,6
10 16 2 8
(ethylene diamine tetra-acetic acid)
C H NO
Phenylalanine 65,4 6,7 8,5
9 11 2
C H NO
Acetanilide 71,1 6,7 10,4
8 9
BBOT (CAS-No 7128-64-5)
C H N O S
72,5 6,1 6,5
26 26 2 2
2,5-bis (5′-tert-butyl-2-benzoxazolyl) thiophene

If these materials are accompanied by a traceable certificate of analysis that includes the uncertainty of the

assigned carbon, hydrogen and nitrogen values, then use the certificate values for calibration purposes. If

pure compounds (> 99,5 % purity) are available, use the stoichiometric values. Store these substances in a

desiccator under conditions that maintain the compounds in a dry state.

Table 1 lists those pure substances that were included in the interlaboratory study (ILS) to determine the

calibration requirements and precision of this International Standard. The ILS indicated benzoic acid is not

suitable for calibration. Pure substances other than those listed in Table 1 can be used for calibration provided

the substances meet the purity and calibration requirements of this International Standard.

5.5 Reference materials.

Reference material coal(s) with a certified composition and uncertainty for carbon, hydrogen and nitrogen may

be used as a check to monitor changes in instrument response, which can be affected by constituents not

present in the calibration materials, and to verify the acceptability of nitrogen results. Alternatively, coal of a

known composition can also be used as a check sample. As the bulk composition of coal can change during

storage, coals shall not be used for calibration.
2 © ISO 2010 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 29541:2010(E)
6 Apparatus

6.1 Analytical instrument, consisting of a furnace, gas handling and detection system capable of

analysing a test portion of 6 mg or greater.

6.2 Balance, stand-alone or integrated with the instrument, with a resolution of a least 0,1 % of the test

portion to be weighed.
7 Preparation of the test sample

The sample shall be the general analysis test sample prepared to a nominal top size of 212 µm using

ISO 13909-4, ISO 13909-6, ISO 18283 or ISO 5069-2. Sample preparation procedures are described in

ISO 13909-4 for coal, ISO 13909-6 for coke and ISO 5069-2 for brown coal and lignites.

The moisture content of each test sample and reference material shall be determined in accordance with

ISO 11722 for coal, ISO 687 for coke or ISO 5068-2 for brown coals and lignites. Alternatively, the test sample

and reference material shall be dried prior to analysis.
8 Procedure
8.1 Instrument set-up

Verify that all instrument operation parameters meet the specifications in the instrument operating manual.

Verify the condition and quantity of all chemicals currently in use in the instrument to ensure they are

satisfactory for the number of samples to be analysed. Prior to any analysis, check for, and if necessary

correct, any leaks in the combustion system and carrier gas system.
8.2 Blank analyses

Perform blank analyses daily to establish carbon, hydrogen and nitrogen levels in the combustion and carrier

gases. The level of nitrogen in these gases shall not exceed 1 % of the instrument nitrogen response for the

lowest mass of calibration material. Repeat blank analyses after changing or renewing gases or other

reagents.
8.3 Conditioning and instrument stability check

Condition the instrument in accordance with the manufacturer's instructions (generally by running at least two

test portions of a coal, coke or brown coal or lignite that have a composition typical of the general analysis

sample
...

DRAFT INTERNATIONAL STANDARD ISO/DIS 29541
ISO/TC 27/SC 5 Secretariat: SA
Voting begins on: Voting terminates on:
2009-04-10 2009-09-10

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION

Solid mineral fuels — Determination of total carbon, hydrogen
and nitrogen content — Instrumental method

Combustibles minéraux solides — Dosage du carbone, de l'hydrogène et de l'azote totaux — Méthode

instrumentale
ICS 73.040; 75.160.10

In accordance with the provisions of Council Resolution 15/1993 this document is circulated in

the English language only.

Conformément aux dispositions de la Résolution du Conseil 15/1993, ce document est distribué

en version anglaise seulement.

To expedite distribution, this document is circulated as received from the committee secretariat.

ISO Central Secretariat work of editing and text composition will be undertaken at publication

stage.

Pour accélérer la distribution, le présent document est distribué tel qu'il est parvenu du

secrétariat du comité. Le travail de rédaction et de composition de texte sera effectué au

Secrétariat central de l'ISO au stade de publication.

THIS DOCUMENT IS A DRAFT CIRCULATED FOR COMMENT AND APPROVAL. IT IS THEREFORE SUBJECT TO CHANGE AND MAY NOT BE

REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.

IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT

INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME STANDARDS TO

WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS.

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.
International Organization for Standardization, 2009
---------------------- Page: 1 ----------------------
ISO/DIS 29541
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall

not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the

unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

Copyright notice

This ISO document is a Draft International Standard and is copyright-protected by ISO. Except as permitted

under the applicable laws of the user's country, neither this ISO draft nor any extract from it may be

reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, photocopying,

recording or otherwise, without prior written permission being secured.

Requests for permission to reproduce should be addressed to either ISO at the address below or ISO's

member body in the country of the requester.
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Reproduction may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
ii ISO 2009 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/DIS 29541
Contents Page

Foreword ............................................................................................................................................................iv

Introduction.........................................................................................................................................................v

1 Scope......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Terms and definitions ...........................................................................................................................1

4 Principle.................................................................................................................................................1

5 Reagents ................................................................................................................................................2

5.1 General ...................................................................................................................................................2

5.2 Carrier gas..............................................................................................................................................2

5.3 Oxygen....................................................................................................................................................2

5.4 Additional reagents...............................................................................................................................2

5.5 Calibration materials.............................................................................................................................2

5.6 Certified reference materials................................................................................................................3

6 Apparatus...............................................................................................................................................3

7 Preparation of the test sample.............................................................................................................3

8 Procedure...............................................................................................................................................3

8.1 Instrument set-up ..................................................................................................................................3

8.2 Blank analyses.......................................................................................................................................3

8.3 Conditioning and instrument stability check .....................................................................................4

8.4 Calibration..............................................................................................................................................4

8.5 Verification of calibration .....................................................................................................................4

8.6 Analysis of test samples.......................................................................................................................4

9 Expression of results............................................................................................................................5

10 Precision................................................................................................................................................6

10.1 Repeatability limit..................................................................................................................................6

10.2 Reproducibility critical difference .......................................................................................................6

11 Test report..............................................................................................................................................6

Annex A Recommendations for calibration (Normative) ...............................................................................7

A.1 Recommended number of calibration points.....................................................................................7

A.2 Recommended calibration masses .....................................................................................................7

A.3 Calibration verification..........................................................................................................................8

A.4 Acceptance of results for certified reference material coal (s) ........................................................9

Annex B Test sample and test results (Informative) ....................................................................................11

B.1 Optimum test sample mass for the determination of total carbon ................................................11

B.2 Checking test results and determining the final quoted result ......................................................12

B.2.1 Checking the acceptability of results obtained under repeatability conditions...........................12

B.2.2 Checking the acceptability of results obtained under reproducibility conditions .......................12

© ISO 2008 – All rights reserved iii
DRAFT 2009
---------------------- Page: 3 ----------------------
ISO/DIS 29541
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.

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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 29541 was prepared by Technical Committee ISO/TC 27, Solid Mineral Fuels, Subcommittee SC 5,

Methods of analysis.

This second/third/... edition cancels and replaces the first/second/... edition (), [Clause (s) / subClause (s) /

table(s) / figure(s) / annex(es)] of which [has / have] been technically revised.

iv © ISO 2008 – All rights reserved
DRAFT 2009
---------------------- Page: 4 ----------------------
ISO/DIS 29541
Introduction

The reliable determination of total carbon, hydrogen and nitrogen is important for engineering calculations

applied to the combustion of coal. The precise and accurate determination of the carbon content of coal is

essential for carbon accounting purposes.
© ISO 2008 – All rights reserved v
DRAFT 2009
---------------------- Page: 5 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 29541
Solid mineral fuels — Determination of total carbon, hydrogen
and nitrogen content — Instrumental method
1 Scope

This Standard specifies a method for the determination of total carbon, hydrogen and nitrogen in coal and

coke by instrumental methods.

NOTE: This standard has been validated in accordance with the principles of ISO 5725 for coal only.

2 Normative references

The following referenced documents are indispensable for the application 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 687, Coke—Determination of moisture in the analysis sample

ISO 1213-2, Solid mineral fuels—Vocabulary, Part 2: Terms relating to sampling, testing and analysis

ISO 5068-2, Brown coals and lignites—Determination of moisture—Indirect gravimetric method,

Part 2: Moisture of analysis sample

ISO 5069-2, Brown coals and lignites—Principles of sampling—Part 2: Sample preparation for determination

of moisture content and for general analysis

ISO 5725-6, Accuracy (trueness and precision) of measurement methods and results Part 6: Use in practice

of accuracy values

ISO 11722, Solid mineral fuels—Hard coal—Determination of moisture in the general analysis test sample by

drying in nitrogen

ISO 13909-4, Hard coal and coke—Mechanical sampling—Part 4: Coal—Preparation of test samples

ISO 13909-6, Hard coal and coke—Mechanical sampling—Part 6: Coke—Preparation of test samples

ISO 18283, Hard coal and coke—Manual sampling
3 Terms and definitions
For the purpose of this Standard, the definitions given in ISO 1213-2 apply.
4 Principle

Carbon, hydrogen and nitrogen are determined concurrently in a single instrumental procedure. The

quantitative conversion of the carbon, hydrogen and nitrogen into their corresponding gases (CO , H O,

2 2
© ISO 2008 – All rights reserved 1
DRAFT 2009
---------------------- Page: 6 ----------------------
ISO/DIS 29541

N /NO ) occurs during combustion of the sample at an elevated temperature in an atmosphere of oxygen.

2 x

Combustion products which would interfere with the subsequent gas analysis are removed. Oxides of nitrogen

(NO ) produced during the combustion are reduced to N before detection. The carbon dioxide, water vapour

x 2

and elemental nitrogen in the gas stream are then determined quantitatively by appropriate instrumental gas-

analysis procedures.
5 Reagents
5.1 General
Unless otherwise specified, all reagents shall be analytical reagent grade.
5.2 Carrier gas
Helium or other suitable gas as specified by the instrument.
5.3 Oxygen
As specified by the instrument.
5.4 Additional reagents
Of types and qualities specified by the instrument.
5.5 Calibration materials

Table 1. Examples of suitable calibration materials and their stoichiometric contents of C, H and N

Mass fraction in percent
Name Formula
Carbon Hydrogen Nitrogen
EDTA
C H N O 41,1 5,5 9,6
10 16 2 8
(ethylene diamine tetra-acetic acid)
Phenylalanine C H NO 65,4 6,7 8,5
9 11 2
Acetanilide C HNO 71,1 6,7 10,4
8 9
BBOT (CAS-No 7128-64-5)
C H N OS 72,5 6,1 6,5
26 26 2 2
2.5-bis (5′-tert-butyl-2-benzoxazolyl) thiophene)

If these materials are accompanied by a traceable certificate of analysis that includes the uncertainty of the

assigned carbon, hydrogen and nitrogen values then use the certificate values for calibration purposes. If pure

compounds (>99,5% purity) are available, use the stoichiometric values. Store these substances in a

desiccator under conditions that maintain the compounds in a dry state.

NOTE: Table 1 includes those pure substances that were included in the interlaboratory study (ILS) employed to

determine the calibration requirements and precision of this standard. This ILS indicated benzoic acid is not suitable for

calibration. Pure substances other than those listed in Table 1 can be used for calibration provided the substances meet

the purity and calibration requirements of this standard.
2 © ISO 2008 – All rights reserved
DRAFT 2009
---------------------- Page: 7 ----------------------
ISO/DIS 29541
5.6 Certified reference materials

Certified reference material (CRM) coal(s) with a certified composition and uncertainty for carbon, hydrogen

and nitrogen may be used as a check to monitor changes in instrument response that can be affected by

constituents not present in the calibration materials and to verify the acceptability of nitrogen results.

Alternatively, coal of a known composition can also be used as a check sample. As the bulk composition of

coal can change during storage, coals shall not be used for calibration.
6 Apparatus
Analytical instrument

An instrument capable of analysing a test portion of 6 mg or greater. It includes a furnace capable of

maintaining a temperature in the range to ensure quantitative recovery of carbon, hydrogen and nitrogen as

their corresponding gases (CO , H O, N /NO ). The combustion gases or a representative aliquot shall be

2 2 2 X

treated to remove or convert any components that can interfere with the measurement of carbon dioxide,

water vapour or nitrogen (produced by the reduction of NO prior to measurement). The detection system shall

include provisions for evaluation of the response in a manner that correlates accurately with the carbon

dioxide, water vapour and nitrogen present in the treated combustion gases.

NOTE Coal contains constituents that can affect the performance of chemicals used to ensure the consistent and

uniform conversion and recovery of carbon, hydrogen and nitrogen.
Balance

A stand-alone balance or a balance integrated with the instrument, with a resolution of a least 0,1% relative of

the test portion to be weighed.
7 Preparation of the test sample

The sample shall be the general analysis sample prepared to a nominal top size of 212 μm using ISO 13909-6,

ISO 18283 or ISO 5069-2. Sample preparation procedures are described in ISO 13909-4 for coal, ISO 13909-

6 for coke and ISO 5069-2 for brown coal and lignites.

The moisture content of each test sample and reference material shall be determined in accordance with

ISO 11722 for coal, ISO 687 for coke or ISO 5068-2 for brown coals and lignites. Alternatively the test sample

and reference material shall be dried prior to analysis.
8 Procedure
8.1 Instrument set-up

Verify all instrument operation parameters meet the specifications in the instrument operating manual. Verify

the condition and quantity of all chemicals currently in use in the instrument to ensure they are satisfactory for

the number of samples to be analysed. Instruments that employ gas to open and close valves shall use extra

dry gas for this purpose. Prior to any analysis check for, and if necessary correct, any leaks in the combustion

system and carrier gas system.
8.2 Blank analyses

Perform blank analyses to establish carbon, hydrogen and nitrogen levels in the combustion and carrier gases.

The level of nitrogen in these gases shall not exceed 1% of the instrument nitrog

...

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