ISO 20289:2018

INTERNATIONAL ISO
STANDARD 20289
First edition
2018-03
Surface chemical analysis — Total
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 2018
© ISO 2018
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Published in Switzerland
ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 3
5 Safety . 3
6 Interferences . 3
7 Apparatus . 3
7.1 General . 3
7.2 Labware . 4
7.3 Drying apparatus . 4
8 Reagents, standards and materials . 4
9 Sample preparation . 5
9.1 Environment . 5
9.2 Sample . 5
9.3 Specimen . 6
9.4 Sample carrier . 6
9.5 Trials/replicates . 6
9.6 Effect of residue mass, size and its position . 7
10 Procedure. 7
10.1 General . 7
10.2 Instrument calibration . 7
10.3 Detection limit . 7
10.4 TXRF measurements . 8
10.5 Spectra fitting . 8
10.6 Unknown samples . 8
11 Qualitative and quantitative analysis . 8
11.1 Identification of elements . 8
11.2 Quantification of elements . 8
11.3 Calculations . 9
11.4 Measurement uncertainty . 9
12 Quality control . 9
13 Precision and accuracy .10
14 Test report .10
Annex A (informative) Uncertainty in TXRF measurements .11
Annex B (informative) Validation of the method .15
Bibliography .19
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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electrotechnical standardization.
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URL: 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.
iv © ISO 2018 – All rights reserved

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 the
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
[1] [2]
and 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.
INTERNATIONAL STANDARD ISO 20289:2018(E)
Surface chemical analysis — Total reflection X-ray
fluorescence analysis of water
1 Scope
This document provides 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 comply with
ISO/IEC 17025.
This document specifies a method to determine the content of elements dissolved in water (for example,
drinking water, surface water and ground water). Taking into account the specific and additionally
occurring interferences, elements can also be determined in waste waters and eluates. Sampling,
dilution and pre-concentration methods are not included in this document.
Elements that can be determined with the present method may change according to the X-ray source of
the instrument. No health, safety or commercial aspects are considered herewith.
The working range depends 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 working range typically covers concentrations between 0,001 mg/l and 10 mg/l,
depending on the element and predefined requirements.
Annex B reports, for example, the complete validation of the method of TXRF analysis of water
performed with instrumentation that has Mo as the X-ray source and uses Ga as the internal standard
for calibration.
Quantification limits 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 3696, Water for analytical laboratory use — Specification and test methods
ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and
sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Guidance on the preservation and handling of water samples
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method
ISO 14706, Surface chemical analysis — Determination of surface elemental contamination on silicon
wafers by total-reflection X-ray fluorescence (TXRF) spectroscopy
ISO 17331, Surface chemical analysis — Chemical methods for the collection of elements from the surface
of silicon-wafer working reference materials and their determination by total-reflection X-ray fluorescence
(TXRF) spectroscopy
ISO/TS 18507:2015, Surface chemical analysis — Use of Total Reflection X-ray Fluorescence spectroscopy
in biological and environmental analysis
JCGM 100 series, Guides to the expression of uncertainty in measurement (GUM series)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3696, ISO 5667-1, ISO 5667-3,
ISO 5725-1, ISO 5725-2, ISO 14706, ISO 17331, ISO/TS 18507, the JCGM 100 series and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
calibration standards
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
detection limit
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.
[SOURCE: ISO 18115-1:2013, 4.168, modified.]
3.5
instrument performance sample
single element or multi-elemental calibration standard used to evaluate the performance of the
instrument with respect to a defined set of criteria
Note 1 to entry: See 8.1.6.
3.6
sample
water solution to be analysed
3.7
specimen
solution containing internal standard prepared for TXRF analysis
3.8
trial/replicate
sample carrier with deposited residue
2 © ISO 2018 – All rights reserved

3.9
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
3.10
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.
3.11
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
DL detection limit
LOQ limit of quantification
PT proficiency test
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 reference file of material risk handling sheets should
be available for the personnel involved.
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 could 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 could 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 could 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
Use one of the following.
7.3.1 Infrared lamp.
7.3.2 Glass ceramic heating plate with a power controller.
7.3.3 Vacuum vessel fitted with gas flow equipment.
7.3.4 Drying temperature should be lower than 60 °C to avoid the loss of volatile elements and
compounds. Due to heat treatment, some elements might 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 % 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 Silicon solution in isopropanol, for example silicon solution (CAS 67-63-0) in isopropanol if the
level of contamination is acceptable.
4 © ISO 2018 – All rights reserved

8.5 Internal standard solution, for example 1 000 mg/l standard solution in 0,5 M nitric acid (CAS
69365-72-6) specified for AAS or ICP.
8.6 Multi-element standard solution, for example 1000 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 ± 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 shall be
passed over the specimen-handling area and exhausted outside the cabinet.
Depending on the purpose of water analysis the environment of sample preparation has to 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 may 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
trials/replicates should be handled in a clean environment (see 9.1).
Preferably normated sampling and stabilization methods shall be selected and reported.
Filtering could 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.
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.
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 can 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 can 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 trial later on.
EXAMPLE Hydrophobization of the reflector: put 10 µl to 30 µl of silicon 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 Trials/replicates
Trials 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 can be rep
...