ISO 20289:2025

Surface chemical analysis - Total reflection X-ray fluorescence analysis of water

This document specifies a chemical method for technicians working with total reflection X-ray fluorescence (TXRF) instrumentation to perform measurements of water samples, according to good practices, with a defined degree of accuracy and precision. Target users are identified among laboratories performing routine analysis of large numbers of samples, which also conform with ISO/IEC 17025. This document specifies a method to determine the content of elements dissolved in water (e.g. drinking water, surface water and ground water). This document is also applicable for determining elements in waste waters and eluates, taking into account the specific and additionally occurring interferences. This document does not specify sampling, dilution and pre-concentration methods. Elements determined using the method specified in this document can depend on the X-ray source of the instrument. This document does not specify health, safety or commercial aspects. The determinable concentrations depend on the matrix and the interferences encountered. In drinking water and relatively unpolluted waters, the limit of quantification lies between 0,001 mg/l and 0,01 mg/l for most of the elements. The range of concentrations typically lies between 0,001 mg/l and 10 mg/l, depending on the element and predefined requirements. Annex A reports an example of uncertainty calculation. Annex B provides an example report on validation of the method for TXRF analysis of water performed with instrumentation that has Mo as the X-ray source and uses Ga as the internal calibration standard. Limits of quantification of most elements are affected by blank contamination and depend predominantly on the laboratory air-handling facilities available, on the purity of reagents and the cleanliness of labware.

Analyse chimique des surfaces — Analyse par fluorescence de rayons X en réflexion totale d'eau

General Information

• Status: Published
• Publication Date: 01-Jun-2025
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: ISO/TC 201/SC 10 - X-ray Reflectometry (XRR) and X-ray Fluorescence (XRF) Analysis
• Drafting Committee: ISO/TC 201/SC 10/WG 1 - XRF technique
• Current Stage: 6060 - International Standard published
• Start Date: 02-Jun-2025
• Due Date: 18-Oct-2025
• Completion Date: 02-Jun-2025

Relations

• Revises: ISO 20289:2018 - Surface chemical analysis - Total reflection X-ray fluorescence analysis of water
• Effective Date: 28-Oct-2023

Overview

ISO 20289:2025 - Surface chemical analysis - Total reflection X‑ray fluorescence analysis of water - specifies a laboratory chemical method for routine TXRF (total reflection X‑ray fluorescence) analysis of water. The standard is aimed at technicians and testing laboratories (particularly those accredited to ISO/IEC 17025) performing high‑throughput elemental analysis of drinking water, surface water, groundwater, waste waters and eluates. It defines good practices, accuracy/precision considerations and reporting requirements for elemental determination using TXRF instrumentation.

Key technical topics and requirements

• Scope and applicability: Quantitative determination of elements dissolved in water using TXRF; does not cover sampling, dilution or pre‑concentration methods, nor health/safety or commercial aspects.
• Instrumentation and calibration: Requirements for instrument calibration, determination of instrumental limit of detection (LOD), and procedures for TXRF measurements and spectra fitting.
• Sensitivity, LOD and LOQ: Typical limits of quantification (LOQ) for drinking and relatively unpolluted waters lie between 0.001 mg/L and 0.01 mg/L for most elements. The measurable concentration range typically spans 0.001 mg/L to 10 mg/L, depending on matrix and element.
• Interferences and matrix effects: Guidance on minimizing interferences (conductivity < 2 mS/cm recommended), handling suspended solids, peak overlaps, pile‑up/sum peaks and reagent/blank contamination.
• Sample preparation and labware: Specifications for clean labware, carrier preparation, drying apparatus options (infrared lamp, heating plate, vacuum vessel) and control of environmental contamination.
• Internal standard and validation examples: Use of internal calibration standards; Annex B provides a validation example using a Mo X‑ray source and Ga as internal standard.
• Quality assurance: Procedures for replicates, quality control samples, precision and accuracy checks, uncertainty estimation (Annex A), and required content for test reports.

Practical applications and users

• Environmental and public‑health laboratories performing routine elemental analysis of water (drinking water compliance, surface/groundwater monitoring).
• Wastewater testing facilities and laboratories analyzing eluates where TXRF advantages (surface sensitivity, small sample volumes) are relevant.
• Laboratories seeking methods compatible with ISO/IEC 17025 accreditation that need standardized TXRF workflows, validation examples and uncertainty calculation guidance.

Related standards

• ISO/TS 18507:2015 - Use of TXRF in biological and environmental analysis (referenced normative guidance).
• ISO/IEC 17025 - Laboratory competence and quality management for routine testing laboratories.

Keywords: ISO 20289, TXRF, total reflection X‑ray fluorescence, water analysis, elemental analysis, limit of quantification, ISO/IEC 17025, method validation, instrument calibration, laboratory quality control.

Standards Content (Sample)

International
Standard
ISO 20289
Second edition
Surface chemical analysis — Total
2025-06
reflection X-ray fluorescence
analysis of water
Analyse chimique des surfaces — Analyse par fluorescence de
rayons X en réflexion totale d'eau
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
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 2
5 Safety . 3
6 Interferences . 3
7 Apparatus . 3
7.1 General .3
7.2 Labware .3
7.3 Drying apparatus .3
8 Reagents, standards and materials . 4
9 Sample preparation . 5
9.1 Environment .5
9.2 Sample .5
9.3 Specimen .5
9.4 Sample carrier .5
9.5 Replicates .6
9.6 Effect of residue mass, size and its position .6
10 Procedure . 6
10.1 General .6
10.2 Instrument calibration .6
10.3 Instrumental limit of detection .7
10.4 TXRF measurements .7
10.5 Spectra fitting.7
10.6 Unknown samples .7
11 Qualitative and quantitative analysis . 8
11.1 Identification of elements .8
11.2 Quantification of elements .8
11.3 Calculations .8
11.4 Measurement uncertainty .8
12 Quality control . 9
13 Precision and accuracy . 9
14 Test report . 9
Annex A (informative) Uncertainty in TXRF measurements .11
Annex B (informative) Validation of the method .15
Bibliography . 19

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
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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)
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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 201, Surface Chemical Analysis, Subcommittee
SC 10, X-ray Reflectometry (XRR) and X-ray Fluorescence (XRF) Analysis.
This second edition cancels and replaces the first edition (ISO 20289:2018) which has been technically
revised.
The main changes are as follows:
— updated Clause 2 and bibliography;
— editorial changes and correction of verbal forms;
— revision of Annex A removing the use of relative uncertainty;
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
Introduction
Total reflection X-ray fluorescence (TXRF) spectroscopy is a surface sensitive technique which can be used
to obtain compositional information about different kinds of samples. ISO/TS 18507 provides guidelines for
the characterization of biological and environmental samples with TXRF.
TXRF is suitable for quantitative elemental analysis of liquid samples deposited as thin films on clean and
[1][2]
well-polished reflectors, by means of internal standard calibration .
This document provides guidance and requirements for the quantitative elemental analysis of water by
means of TXRF instrumentation.

v
International Standard ISO 20289:2025(en)
Surface chemical analysis — Total reflection X-ray
fluorescence analysis of water
1 Scope
This document specifies a chemical method for technicians working with total reflection X-ray fluorescence
(TXRF) instrumentation to perform measurements of water samples, according to good practices, with a
defined degree of accuracy and precision. Target users are identified among laboratories performing routine
analysis of large numbers of samples, which also conform with ISO/IEC 17025.
This document specifies a method to determine the content of elements dissolved in water (e.g. drinking
water, surface water and ground water). This document is also applicable for determining elements in waste
waters and eluates, taking into account the specific and additionally occurring interferences. This document
does not specify sampling, dilution and pre-concentration methods.
Elements determined using the method specified in this document can depend on the X-ray source of the
instrument. This document does not specify health, safety or commercial aspects.
The determinable concentrations depend on the matrix and the interferences encountered. In drinking
water and relatively unpolluted waters, the limit of quantification lies between 0,001 mg/l and 0,01 mg/l for
most of the elements. The range of concentrations typically lies between 0,001 mg/l and 10 mg/l, depending
on the element and predefined requirements.
Annex A reports an example of uncertainty calculation. Annex B provides an example report on validation of
the method for TXRF analysis of water performed with instrumentation that has Mo as the X-ray source and
uses Ga as the internal calibration standard.
Limits of quantification of most elements are affected by blank contamination and depend predominantly
on the laboratory air-handling facilities available, on the purity of reagents and the cleanliness of labware.
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/TS 18507:2015, Surface chemical analysis — Use of Total Reflection X-ray Fluorescence spectroscopy in
biological and environmental analysis
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 18507 and the following apply.
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/
3.1
calibration standard
known standard solutions, prepared from the primary dilution solution or stock solutions, containing the
elements of interest or the internal standard element

3.2
linear calibration range
concentration range over which the instrument response is linear
3.3
sensitivity
slope of the linear fitting of the analytical curves, functional relationship between fluorescence intensity
and concentration
3.4
limit of detection
minimum element concentration that can be identified with 99 % confidence that the element concentration
is different from the blank
Note 1 to entry: See 10.3.
3.5
sample
water solution to be analysed
3.6
specimen
solution containing internal standard prepared for TXRF analysis
3.7
replicate
sample carrier with deposited residue
3.8
internal standard content
known amount of an element used to normalize the variation in the fluorescence X-ray intensities of the
other elements in a residue
3.9
quality control sample
reference material obtained from an outside source, with known element concentrations used to check
accuracy and precision
Note 1 to entry: See Clause 12.
3.10
limit of quantification
smallest concentration of an element that can be reliably quantified
Note 1 to entry: See 11.2.
4 Symbols and abbreviated terms
C concentration (or mass per volume density) in mg/l
LOD limit of detection
LOQ limit of quantification
RSD relative standard deviation
S sensitivity
TXRF total reflection X-ray fluorescence

5 Safety
This test method uses X-ray radiation. Consequently, it is important to avoid exposing any part of the body
to the X-rays produced by the apparatus. A risk assessment and materials safety data sheets (MSDS or SDS)
should be readily available.
6 Interferences
The electrical conductivity of the water sample to be analysed should be lower than 2 mS/cm. The presence
of particles and suspended solids can affect accuracy and precision of TXRF analysis due to self-absorption
effects. Sea water or matrix rich wastewaters may be diluted or filtered to reduce possible interferences
(see 9.2) and background contributions (see 10.3). All the reagents shall be analysed to check the possible
presence of impurities. Interferences can be caused by contaminant elements due to uncleaned glassware
(see 7.1), sample preparation environment (see 9.1) or reflectors (see 9.4). Pile-up or sum peaks can arise if
some elements are present in high concentration. Peaks overlap should be considered.
7 Apparatus
7.1 General
For reagents and specimen preparation, use ordinary laboratory glassware or plasticware unless otherwise
stated. The apparatus for preparation of the samples shall be calibrated and cleaned.
Check periodically the accuracy of micropipettes and volumetric flasks used in the volumetric method,
by taking an exact volume of water with the micropipette and weighing it on a high-precision calibrated
balance. The corresponding relative standard deviation (RSD) of all the micropipettes and glassware used
shall be indicated and considered for the calculation of the overall method RSD.
7.2 Labware
The use of uncoloured material is preferable.
7.2.1 One-mark volumetric flasks, 10,00 ml ± 0,02 ml, made of glass, PE, PFA or PP.
7.2.2 Plastic micropipettes, from 1 μl to 10 μl and from 100 μl to 1 000 μl (minimum accuracy 2 %),
made of PE, PFA or PP.
7.2.3 Plastic beakers, 100 ml and 1 000 ml, made of PE, PFA, PP or PTFE.
7.2.4 Plastic test tubes, 1,5 ml, 50 ml and 100 ml, made of PE, PFA, PP or PTFE.
7.2.5 Syringe with 0,2 µm pore size filters.
7.2.6 Carrier-stand made of PFA or PTFE.
7.3 Drying apparatus
7.3.1 Use one of the following.
a) Infrared lamp.
b) Glass ceramic heating plate with a power controller.
c) Vacuum vessel fitted with gas flow equipment.

7.3.2 Drying temperature should be lower than 60 °C to avoid the loss of volatile elements and compounds.
Due to heat treatment, some elements can evaporate or diffuse into the X-ray reflector. Therefore, the
recovery rate for elements has to be determined especially for fast diffusers, for example Cu or Ni, or for
most volatile elements and/or compounds, such as As, Cl, Hg or SiF.
8 Reagents, standards and materials
Use only reagents of recognized analytical grade and only bi-distilled water or water of equivalent purity.
The level of contamination of blanks shall be periodically checked and taken into account for quantification.
8.1 Ultra-pure water, for example water with conductivity less than 0,05 µS/cm, commercially available
or obtained by purification systems.
8.2 Ultra-pure nitric acid, for example nitric acid (CAS 7697-37-2) solution with concentration from 65 %
wt to 70 % wt.
8.3 Cleaning solution, for example liquid detergent, concentrated, alkaline and foaming, suitable for
manual cleaning, soaking, ultrasonic baths and brushes systems (CAS 1310-73-2).
8.4 Silicone solution in isopropanol, for example silicone solution (CAS 67-63-0) in isopropanol if the
level of contamination is acceptable.
8.5 Internal standard solution, for example 1 000 mg/l standard solution in 0,5 mol/l nitric acid (CAS
69365-72-6) specified for AAS or ICP.
8.6 Multi-element standard solution, for example 1 000 mg/l standard solution in nitric acid specified
for AAS or ICP containing elements of interest.
8.7 Diluted internal standard solutions
The internal standard content in the specimen should be comparable to the amount of element to be
quantified. Diluted internal standard solutions may be necessary to add a defined sample amount to prepare
the specimen. Prepare fresh diluted internal standard solutions, either by volume or, preferably, by weight
starting from internal standard solutions (8.5). Select the right dilution steps required to obtain the final
defined concentration of internal standard element in the specimen. Take into account the accuracy of all
the steps involved. Check the contamination level of the prepared solutions and take it into account for
quantification.
EXAMPLE Diluted gallium internal standard solution 100 mg/l gallium solution
Prepare diluted gallium standard solution using either method a) or method b) below.
a) Transfer 1 000 μl of gallium standard solution (8.5) to a plastic or glass 10 ml one-mark volumetric flask (7.2.1)
with a plastic micropipette (7.2.2), add under 9 ml of ultra-pure water (8.1), finally make up to the mark with
ultra-pure water (8.1) and mix.
b) Weigh a 10 ml plastic beaker (7.2.3) to the nearest 0,001 g. Transfer 1 000 μl of gallium standard solution (8.5)
to the beaker with a plastic micropipette (7.2.2), add under 9 ml of ultra-pure water (8.1), finally add ultra-pure
water (8.1) to make the mass up to 10 g (plus the mass of the beaker) to the nearest 0,01 g and mix.
8.8 Validity of reference material
The validity of the reference material (for example the expiration date) should also be checked.
The use of calibrated balances is recommended. Precision should be indicated and considered for the overall
method uncertainty estimation (for example 10,0 mg ± 0,5 mg).

9 Sample preparation
9.1 Environment
Cabinets meeting the requirements for ISO class 4 or better are recommended, but not compulsory, both
for sample preparation and measurements. The use of a vertical laminar flow cabinet is strongly suggested
for sample preparation. For reasons of cleanliness and operator safety, clean air must be passed over the
specimen-handling area and exhausted outside the cabinet.
Depending on the purpose of water analysis, the environment of sample preparation should be checked for
contamination.
9.2 Sample
When the pH value of the sample changes drastically, precipitation and other phenomena affecting the
homogeneity and representativeness of the sample can occur, and this should be avoided. If water samples
have been previously stabilized, dilution effects and contamination levels of the blanks used should be
considered for quantification. Where appropriate, samples with high turbidity may be filtered through
0,2 µm pore size filters. Only clean, uncoloured and, preferably, sterile plastic test tubes shall be used to
keep and store water samples, to avoid contamination. Samples, specimens and replicates should be handled
in a clean environment (see 9.1).
Preferably, normated sampling and stabilization methods should be selected and reported.
Filtering can remove contamination from the original sample, resulting in incorrect quantification. This
step should be carefully evaluated and reported.
9.3 Specimen
Specimens are prepared by adding a defined amount of internal standard solution to the right sample
amount required to obtain the selected concentration of internal standard element.
For quantitative analysis, at least three independent specimens for each water sample to be analysed should
be prepared.
EXAMPLE Specimen preparation: each specimen is a gallium diluted solution with 1 mg/l gallium concentration,
prepared according to one of the procedures described below.
a) Volume procedure: Transfer 10 μl of diluted gallium calibration solution 100 mg/l to a single-use 1,5 ml plastic
tube. With a plastic micropipette add 990 μl of the water sample to be analysed. Carefully vortex the tube for
2 min to 3 min for complete homogenization.
b) Weight procedure: Weigh a single-use 1,5 ml plastic tube to the nearest 0,001 g. Transfer 10 μl of diluted gallium
calibration solution 100 mg/l to the plastic tube with a plastic micropipette, then add the water sample to be
analysed to make the mass up to 1 g (plus the mass of the plastic tube to the nearest 0,001 g). Carefully vortex the
tube for 2 min to 3 min for complete homogenization.
9.4 Sample carrier
All reflectors described in ISO/TS 18507:2015, 6.2 may be used as sample carriers. It is recommended
that the reflector surface is hydrophobic (i.e. contact angle with water higher than 90°) in order to have a
more regular residue shape. If the reflector surface is hydrophilic (i.e. contact angle with water lower than
90°) it should be siliconized according to the procedure described in the example below. Reflector surface
hydrophobization is preferred; however, reflectors may also be used without any specific preparation. The
surface roughness of the reflector affects measurement background, and thus analysis results. It is advisable
to check the surface quality of the reflectors by monitoring the background increase with time and use.
If non-disposable carriers are in use, suitable cleaning procedures, as described in ISO/TS 18507:2015, 6.2.2,
shall be performed. Only clean reflectors should be used. The level of contamination should be determined

by TXRF and taken into account for quantification. A procedure to determine contamination consists of
measuring the reflector in the same conditions as the replicate later on.
EXAMPLE Hydrophobization of the reflector: put 10 µl to 30 µl of silicone solution in the centre of the reflector at
room temperature and let it dry for 30 min at 60 °C with a drying apparatus.
9.5 Replicates
Replicates are prepared by depositing a defined volume of liquid in the centre of the reflector area facing the
detector and letting it dry. This procedure may be repeated multiple times manually or automatically.
It is possible to apply a larger volume of water sample with low matrix content. The maximum volume of
one pipetting step should not exceed 10 µl due to the size of the resulting sample spot. Manual repetitive
pipetting of a few µl or a dispensing device pipetting µl droplets provides a better and more homogeneous
sample spot.
For quantitative analysis, at least three replicates should be prepared from each spec
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