ISO 622:2025

Coal and coke - Determination of phosphorus - Reduced molybdophosphate photometric method

This document specifies a reduced molybdophosphate photometric method for the determination of the total phosphorus mass fraction of hard coal, lignites and coke. Two methods for taking the phosphorus into solution are specified, namely extraction from the coal or coke ash with acid or by repeated oxidation of the coal or coke, by acid, to remove carbonaceous matter.

Charbon et coke — Détermination du phosphore — Méthode photométrique au molybdophosphate réduit

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 622:2016 - Solid mineral fuels - Determination of phosphorus content - Reduced molybdophosphate photometric method
• Effective Date: 27-May-2023

Overview

ISO 622:2025 - "Coal and coke - Determination of phosphorus - Reduced molybdophosphate photometric method" specifies a laboratory method for measuring the total phosphorus mass fraction in hard coal, lignite and coke. The standard defines two validated extraction routes to take phosphorus into solution (ash acid extraction or repeated wet oxidation) and a photometric determination based on the formation of reduced molybdophosphate (blue complex) whose absorbance is measured by a spectrophotometer.

This third edition updates scope, normative references and calculation formulae, and adds a detailed test report requirement.

Key topics and requirements

• Scope and samples: Analysis sample prepared and ground to pass a 212 µm sieve, taken and prepared per ISO sampling standards. Ash is prepared per ISO 1171 when using the dry-ash extraction route.
• Two extraction methods:
  • Dry oxidation (ash extraction): ash the sample, grind to pass 63 µm, extract with hydrofluoric acid (HF) and sulfuric acid (H2SO4).
  • Wet oxidation: repeated oxidation of the coal/coke with nitric acid (HNO3) in the presence of sulfuric acid to remove carbonaceous matter.
• Photometric determination: add ammonium molybdate and ascorbic acid (with antimony potassium tartrate as accelerator) to produce the reduced molybdophosphate blue; measure absorbance with a spectrophotometer or photoelectric absorptiometer.
• Reagents and apparatus: lists analytical-grade reagents (HF, H2SO4, HNO3, molybdate, ascorbic acid, standards) and apparatus (muffle furnace, platinum crucible, Kjeldahl flask assembly for wet digestion, spectrophotometer).
• Safety notes: strong warnings for handling hydrofluoric acid (highly corrosive and toxic) and heat generation when preparing sulfuric acid dilutions.
• Quality and performance: clauses on precision (repeatability and reproducibility) and requirements for reagent blanks, calibration (standard phosphorus solutions) and expression of results.
• Reporting: updated Clause 11 specifies required information in the test report.

Applications and users

ISO 622:2025 is used for:

• Quality control in coal and coke production and trading
• Laboratory analysis in power generation, metallurgical coke plants, and coal research
• Environmental monitoring and regulatory compliance where phosphorus content affects ash behavior, slagging or emissions
• Instrument and reagent suppliers for method validation and product guidance

Typical users: analytical chemists, coal testing laboratories, QA/QC managers, plant technical teams, environmental laboratories and standards bodies.

Related standards

Normative references include ISO 1171 (ash), ISO 565 (sieves), ISO 18283 and ISO 13909 series (sampling and sample preparation), and ISO 383 (lab glassware). Reference ISO 622:2016 for prior edition comparisons.

Standards Content (Sample)

International
Standard
ISO 622
Third edition
Coal and coke — Determination
2025-06
of phosphorus — Reduced
molybdophosphate photometric
method
Charbon et coke — Détermination du phosphore — Méthode
photométrique au molybdophosphate réduit
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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Phone: [phone]
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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
4.1 Extraction .1
4.2 Determination .2
5 Reagents . 2
6 Apparatus . 3
7 Sample preparation . 4
8 Procedure . 4
8.1 Dry oxidation method .4
8.2 Wet oxidation method .5
8.3 Determination .6
9 Expression of results . 6
10 Precision of the method . 7
10.1 Repeatability .7
10.2 Reproducibility .7
11 Test report . 7

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 622:2016), which has been technically
revised.
The main changes are as follows:
— the title and scope have been modified to specifically refer to coal;
— the normative references have been updated;
— Formulae (1) and (2) have been modified;
— a new Formula (3) has been added in Clause 9;
— a new test report clause (Clause 11) has been added.
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 622:2025(en)
Coal and coke — Determination of phosphorus — Reduced
molybdophosphate photometric method
1 Scope
This document specifies a reduced molybdophosphate photometric method for the determination of the
total phosphorus mass fraction of hard coal, lignites and coke. Two methods for taking the phosphorus into
solution are specified, namely extraction from the coal or coke ash with acid or by repeated oxidation of the
coal or coke, by acid, to remove carbonaceous matter.
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 383, Laboratory glassware — Interchangeable conical ground joints
ISO 565, Test sieves — Metal wire cloth, perforated metal plate and electroformed sheet — Nominal sizes of
openings
ISO 1171, Coal and coke — Determination of ash
ISO 13909-2, Coal and coke — Mechanical sampling — Part 2: Sampling of coal from moving streams
ISO 13909-3, Coal and coke — Mechanical sampling — Part 3: Sampling of coal from stationary lots
ISO 13909-4, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 13909-5, Coal and coke — Mechanical sampling — Part 5: Sampling of coke from moving streams
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
4.1 Extraction
Method 1: Removal of carbonaceous material by ashing in a muffle furnace under specified conditions, and
extraction of phosphorus by treatment of the ash obtained with hydrofluoric and sulfuric acids.

Method 2: Removal of carbonaceous material by repeated oxidation with nitric acid in the presence of
sulfuric acid.
4.2 Determination
Addition of ammonium molybdate and ascorbic acid solution to the acid solution. Measurement of the
absorbance of the resulting blue solution by a suitable optical instrument.
5 Reagents
During the analysis, use only reagents of recognized analytical grade and only distilled water or water of
equivalent purity.
5.1 Hydrofluoric acid, approximately 400 g/l solution.
WARNING — Aqueous hydrofluoric acid is a highly corrosive liquid which attacks glass; the vapour
is irritant and toxic. Its reaction with the skin and eyes is strongly corrosive, producing severe
and painful burns which can not be immediately evident and which respond slowly to treatment.
The solution shall be handled only inside a well-ventilated fume cupboard. In the event of contact
or suspected contact, flood with water and seek immediate medical attention. The manufacturer’s
literature should be consulted for further information.
WARNING — Preparation of solutions using sulfuric acid can generate significant heat. Generation of
heat can be reduced by adding sulfuric acid as the last component of a solution mixture.
5.2 Sulfuric acid, concentrated, ρ 1,84 g/ml, approximately 98 % mass concentration solution.
5.3 Sulfuric acid, solution, prepared by diluting approximately 490 g of sulfuric acid (5.2) to a volume of
1 l with water.
5.4 Nitric acid, concentrated, ρ 1,42 g/ml, approximately 70 % mass concentration solution.
5.5 Ammonium molybdate, 60 g/l solution.
5.6 Ascorbic acid, 50 g/l solution.
Prepare the solution fresh daily.
5.7 Antimony potassium tartrate (KSbO·C H O ), 1,36 g/l solution.
4 4 6
5.8 Reagent blank solution.
Mix 25 ml of the sulfuric acid solution (5.3), 10 ml of the ammonium molybdate solution (5.5), 10 ml of
the ascorbic acid solution (5.6) and 5 ml of the antimony potassium tartrate solution (5.7). Prepare fresh
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