ISO 20289:2025

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
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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
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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)
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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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