ISO 11723:2025
(Main)Coal and coke — Determination of arsenic and selenium — Eschka's mixture and hydride generation method
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
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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
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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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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 0,4 g of sodium hydroxide (NaOH) into a plastic bottle of 125 ml capacity and add 100 ml of
distilled water. Prepare freshly on the day of use. Alternatively, commercially available pressed pellets of
sodium borohydride may be used.
5.6 Arsenic stock solution (100 mg/l). Dissolve 0,132 0 g ± 0,000 5 g of arsenic trioxide (As O of 99,9 %
2 3
purity, dried at 110 °C for 1 h) in 25 ml of 20 % KOH solution. Add approximately 50 ml of water and 20 ml of
hydrochloric acid (5.2). Adjust the volume with water to 1 litre in a volumetric flask. Alternatively, dissolve
0,416 5 g ± 0,000 5 g of sodium arsenate dibasic heptahydrate (Na HAsO .7H O) in approximately 100 ml of
2 4 2
water. Add 10 ml of hydrochloric acid (5.2) and adjust the volume with water to 1 l in a volumetric flask.
NOTE A commercially available certified stock solution can be used as an alternative.
5.7 Dilute arsenic stock solution (1 mg/l). Transfer 5 ml of arsenic stock solution to a 500 ml volumetric
flask. Add approximately 100 ml of water and 5 ml of hydrochloric acid (5.2). Adjust to volume with water.
5.8 Arsenic working standard (50 μg/l). Transfer 5 ml of dilute arsenic stock solution (5.7) to a 100 ml
volumetric flask. Add approximately 20 ml of water and of 1 ml hydrochloric acid (5.2). Adjust to volume
with water. Prepare freshly on the day of measurement.
5.9 Selenium stock solution (100 mg/l). Dissolve 0,100 0 g ± 0,000 5 g of elemental selenium (of 99,9 %
purity) in a minimum of nitric acid in a beaker. Evaporate to dryness. Add 2 ml of water and evaporate
to dryness; repeat this procedure twice. Add 10 ml of water to the residue and 10 ml of hydrochloric
acid (5.2). Dissolve the residue by heating. Allow the solution to cool and adjust the volume with water
to 1 l in a volumetric flask. Alternatively, dissolve 0,467 4 g ± 0,000 5 g of sodium selenate decahydrate
(Na SeO .10H O) in approximately 100 ml of water. Add 10 ml of hydrochloric acid (5.2) and adjust the
2 4 2
volume with water to 1 l in a volumetric flask.
NOTE A commercially available certified stock solution can be used as an alternative.
5.10 Dilute selenium stock solution (1 mg/l). Transfer 5 ml of selenium stock solution (5.9) to a 500 ml
volumetric flask. Add approximately 100 ml of water and 5 ml of hydrochloric acid (5.2). Adjust to volume
with water.
5.11 Selenium working standard (50 μg/l). Transfer 5 ml of dilute selenium stock solution (5.10) to a
100 ml volumetric flask. Add approximately 20 ml of water and 1 ml of hydrochloric acid (5.2). Adjust to
volume with water. Prepare freshly on the day of measurement.
6 Apparatus
6.1 Balance, capable of weighing to the nearest 0,1 mg.
6.2 Crucible
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