ISO 11723:2025

Coal and coke - Determination of arsenic and selenium - Eschka's mixture and hydride generation method

This document specifies a method using Eschka's mixture during ashing, extraction of the ash residue with acid, and hydride generation atomic absorption spectrometry or hydride generation atomic fluorescence spectrometry, for the determination of arsenic and selenium in solid mineral fuels. The method is also applicable for the determination of the analytes by hydride generation inductively coupled plasma atomic emission spectrometry.

Charbon et coke — Détermination de l'arsenic et du sélénium — Mélange d'Eschka et méthode par production d'hydrure

General Information

• Status: Published
• Publication Date: 24-Jun-2025
• ICS: 73.040 - Coals
• ICS: 75.160.10 - Solid fuels
• Technical Committee: ISO/TC 27/SC 5 - Methods of analysis
• Drafting Committee: ISO/TC 27/SC 5 - Methods of analysis
• Current Stage: 6060 - International Standard published
• Start Date: 25-Jun-2025
• Due Date: 20-May-2026
• Completion Date: 25-Jun-2025

Relations

• Revises: ISO 11723:2016 - Solid mineral fuels - Determination of arsenic and selenium - Eschka's mixture and hydride generation method
• Effective Date: 27-May-2023

Overview

ISO 11723:2025 defines a standardized laboratory method for the determination of arsenic and selenium in solid mineral fuels (coal and coke). The method combines ashing with Eschka's mixture, acid extraction of the ash residue, and hydride generation coupled to atomic spectrometric detection: hydride generation atomic absorption spectrometry (HG-AAS), hydride generation atomic fluorescence spectrometry (HG-AFS), or hydride generation inductively coupled plasma atomic emission spectrometry (HG‑ICP‑AES).

This procedure is intended for reliable trace-level analysis of these toxic elements in quality control, environmental monitoring and regulatory compliance for the coal and coke sectors.

Key Topics

• Principle: Sample is ignited with Eschka's mixture in an oxidizing atmosphere to remove organics, the residue is dissolved in hydrochloric acid, and arsenic/selenium are determined using hydride generation and atomic spectrometry.
• Sample preparation: Typical test portion ~0.5 g mixed with specified masses of Eschka's mixture; controlled muffle furnace ashing at 800 °C; extraction with HCl and gravimetric dilution to a defined mass or volume.
• Reagents and standards: Use of analytical-grade reagents, defined stock and working standards for arsenic and selenium, freshly prepared sodium borohydride reducing solution and potassium iodide for arsenic measurements.
• Measurement: Instrument optimization is performed per manufacturer guidance. Reported analytical wavelengths in the standard: As at 193.7 nm and Se at 196.0 nm. Hydride generation improves sensitivity and reduces matrix effects for volatile hydride-forming elements.
• Quality controls: Blank determinations are performed concurrently. Calibration standards are prepared in a matrix-matched Eschka blank. Duplicate test portions and method blanks support traceability.

Applications

• Routine laboratory determination of arsenic and selenium in coal and coke for:
  • Environmental monitoring and emissions control
  • Product quality and safety assessment
  • Compliance with regulatory limits and reporting
• Beneficial where low detection limits and reduced spectral interferences are required; hydride generation is particularly effective for volatile species and trace analysis.

Related Standards

• ISO 687 - Moisture determination for coke analysis sample
• ISO 1170, ISO 3696 - Calculation and laboratory water quality requirements
• ISO 13909 series and ISO 18283 - Sampling and preparation of test samples for coal and coke

Practical value: Implementing ISO 11723:2025 ensures a harmonized, reproducible approach to trace arsenic and selenium analysis in solid mineral fuels, facilitating consistent results across laboratories and supporting regulatory and commercial decision-making.

Standards Content (Sample)

International
Standard
ISO 11723
Third edition
Coal and coke — Determination
2025-06
of arsenic and selenium —
Eschka's mixture and hydride
generation method
Charbon et coke — Détermination de l'arsenic et du sélénium —
Mélange d'Eschka et méthode par production d'hydrure
Reference number
© 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
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or ISO’s member body in the country of the requester.
ISO copyright office
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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 Preparation of the test sample. 3
8 Procedure . 3
8.1 Blank determination .3
8.2 Preparation of test solution .3
8.3 Preparation of calibration standards .4
8.4 Preparation for measurement .4
8.4.1 General .4
8.4.2 Arsenic .4
8.4.3 Selenium . .4
9 Measurement by atomic absorption or atomic fluorescence spectrometry after hydride
generation . 4
10 Expression of results . 5
11 Precision . 5
11.1 Repeatability .5
11.2 Reproducibility critical difference .6
11.3 Test report .6

iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
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of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
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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 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This third edition cancels and replaces the second edition (ISO 11723:2016), which has been technically
revised.
The main changes are as follows:
— the normative references have been updated;
— Formulae (1) and (2) have been clarified.
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 11723:2025(en)
Coal and coke — Determination of arsenic and selenium —
Eschka's mixture and hydride generation method
1 Scope
This document specifies a method using Eschka's mixture during ashing, extraction of the ash residue with
acid, and hydride generation atomic absorption spectrometry or hydride generation atomic fluorescence
spectrometry, for the determination of arsenic and selenium in solid mineral fuels.
The method is also applicable for the determination of the analytes by hydride generation inductively
coupled plasma atomic emission spectrometry.
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 687, Coke — Determination of moisture in the general analysis test sample
ISO 1170, Coal and coke — Calculation of analyses to different bases
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 5068-2, Brown coals and lignites — Determination of moisture — Part 2: Indirect gravimetric method for
moisture in the analysis sample
ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test sample by
drying in nitrogen
ISO 13909-4, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 13909-6, Coal and coke — Mechanical sampling — Part 6: Preparation of test samples of coke
ISO 18283, Coal and coke — Manual sampling
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
A known mass of the sample is ignited in intimate contact with Eschka's mixture in an oxidizing atmosphere
at 800 °C to remove the organic matter. The residue is then extracted with hydrochloric acid and the
analytes determined by hydride generation atomic absorption spectrometry or hydride generation atomic
fluorescence spectrometry.
5 Reagents
WARNING — Care shall be exercised when handling reagents, many of which are toxic and corrosive.
During the analysis, unless otherwise stated, use only reagents of recognized analytical reagent grade and
water conforming to Grade 1 of ISO 3696.
5.1 Eschka's mixture, composed of two parts by mass of light magnesium oxide and one part by mass of
anhydrous sodium carbonate.
5.2 Hydrochloric acid (ρ 1,19 g/ml).
5.3 Nitric acid (ρ 1,42 g/ml).
5.4 Potassium iodide solution, 500 g/l. Dissolve 50 g of analytical reagent (AR) grade KI in distilled
water and adjust the volume to 100 ml (for determination of As).
5.5 Sodium borohydride solution. Determine its mass by weighing 1,50 g of sodium borohydride
(NaBH ) and
...