Microbeam analysis — Electron probe microanalyser (EPMA) — Guidelines for performing quality assurance procedures

This document provides guidelines for performing routine diagnostics and quality assurance procedures on electron probe microanalysers (EPMA). It is intended to be used periodically by an instrument's operator to confirm that the instrument is performing optimally, and to aid in troubleshooting if it is not. It covers the properties of reference materials required and the analysis procedures necessary to independently test and fully evaluate the functionality of the main components of an EPMA system. The analytical procedure described herein is distinct from single-element diagnostic procedures, which can be performed more rapidly. Such procedures are valid for the diffractor position and conditions under which the test is performed, whereas the procedure described herein is intended to qualify an instrument's capabilities for exploratory analysis of unknowns, trace analysis and non-routine work (such as peak interferences). This document is applicable to EPMA and other wavelength dispersive spectrometer (WDS) systems in which elemental identification and quantification are performed by analysis of the energy and intensity of the characteristic X-ray lines observed in wavelength-dispersed X-ray spectra. It is not directly applicable to elemental analysis using energy dispersive spectrometry (EDS).

Analyse par microfaisceaux — Analyse par microsonde électronique (microsonde de Castaing) — Lignes directrices pour la mise en œuvre des procédures d'assurance qualité

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INTERNATIONAL ISO
STANDARD 19463
First edition
2018-07
Microbeam analysis — Electron probe
microanalyser (EPMA) — Guidelines
for performing quality assurance
procedures
Analyse par microfaisceaux — Analyse par microsonde électronique
(microsonde de Castaing) — Lignes directrices pour la mise en œuvre
des procédures d'assurance qualité
Reference number
ISO 19463:2018(E)
ISO 2018
---------------------- Page: 1 ----------------------
ISO 19463:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

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

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Published in Switzerland
ii © ISO 2018 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 19463:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 General principles of electron probe microanalyser quality assurance (EPMA QA) .....................6

4.1 Objective ....................................................................................................................................................................................................... 6

4.2 Selection of challenge materials............................................................................................................................................... 6

4.2.1 General...................................................................................................................................................................................... 6

4.2.2 General characteristics of analysed materials ........................................................................................ 6

4.2.3 Specific characteristics of challenge materials ...................................................................................... 7

4.3 QA measurement parameters .................................................................................................................................................... 7

4.3.1 General...................................................................................................................................................................................... 7

4.3.2 Laboratory environment preparation ........................................................................................................... 7

4.3.3 Instrument parameters .............................................................................................................................................. 8

4.4 Data acquisition ..................................................................................................................................................................................11

4.5 Frequency of QA diagnostic testing ....................................................................................................................................12

5 Test report ................................................................................................................................................................................................................12

6 Data analysis and performance tracking .................................................................................................................................13

6.1 General ........................................................................................................................................................................................................13

6.2 Quantitative analysis of the challenge material .......................................................................................................13

6.3 Calculation of means and standard deviations ........................................................................................................13

6.4 Statistical tests performed on data .....................................................................................................................................13

6.4.1 General...................................................................................................................................................................................13

6.4.2 Normality test ...................................................................... ............................................................................................14

6.4.3 Variance test .....................................................................................................................................................................14

Annex A (informative) Examples of challenge materials and reference materials for EPMA

WDS QA ........................................................................................................................................................................................................................15

Annex B (informative) Distinguishing specimen preparation effects from instrument

malfunction .............................................................................................................................................................................................................17

Annex C (informative) Graphical rendering of data and control charting .................................................................21

Annex D (informative) Failure modes indicated by test results ............................................................................................26

Bibliography .............................................................................................................................................................................................................................30

© ISO 2018 – All rights reserved iii
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ISO 19463:2018(E)
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 has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely 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 documents 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).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

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 202, Microbeam analysis, Subcommittee

SC 2, Electron probe microanalysis.

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 © ISO 2018 – All rights reserved
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ISO 19463:2018(E)
Introduction

This document was developed to provide a general method for operators of electron probe

microanalysers (EPMA) to perform the most complete and reliable instrument diagnostic routine

possible in the smallest amount of operator time, instrument time and analysis time. Performing this

procedure on their instruments at regularly scheduled intervals will allow the operator to track the

quality of an instrument’s elemental qualitative and quantitative performance, and alert the operator of

the need for instrument service and calibration shortly after it fails to meet its operating specifications

for measurement uncertainty. With equal application of this document to the diagnostics procedure

of multiple instruments in a single laboratory, or even multiple instruments managed by different

operators in separate laboratories, analysis results can be normalized between instruments using the

performance comparison, facilitating analytical reproducibility.

The chief product of an analytical laboratory quality assurance (QA) program, ultimately, is confidence

– confidence that the analysis of any specimen sent to any laboratory participating in the program

will be consistent, correct within tolerance and interchangeable with equivalent analyses of related

specimens performed by any other laboratory in the program. In order to maximize confidence, the QA

tests and test materials chosen should evaluate the broadest possible range of instrument functionality.

In the context of EPMA, this means testing not only the stability of the electron gun and the function of

the photon counters, but also the functionality of every component of each wavelength spectrometer

mounted to the system. This includes the numerous types of diffracting crystals that disperse the

X-rays, the mechanical components that switch the spectrometer from one crystal to another, and the

drive mechanisms that scan the crystal through a spectral region of interest. Since these spectrometer

components can fail independently of the others, and many such failures will not be noticeable in all

measurements, a complete QA test will include materials that generate X-ray lines that span the range of

any diffracting crystal and methods to properly analyse them. It will therefore generate the maximum

possible information on the instrument’s functional integrity. From this information, instrument

performance can be optimized, thereby obtaining maximum analytical confidence. The procedures and

reference material attributes outlined in this document are designed to achieve these goals.

© ISO 2018 – All rights reserved v
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INTERNATIONAL STANDARD ISO 19463:2018(E)
Microbeam analysis — Electron probe microanalyser
(EPMA) — Guidelines for performing quality assurance
procedures
1 Scope

This document provides guidelines for performing routine diagnostics and quality assurance procedures

on electron probe microanalysers (EPMA). It is intended to be used periodically by an instrument’s

operator to confirm that the instrument is performing optimally, and to aid in troubleshooting if it is

not. It covers the properties of reference materials required and the analysis procedures necessary to

independently test and fully evaluate the functionality of the main components of an EPMA system.

The analytical procedure described herein is distinct from single-element diagnostic procedures, which

can be performed more rapidly. Such procedures are valid for the diffractor position and conditions

under which the test is performed, whereas the procedure described herein is intended to qualify an

instrument’s capabilities for exploratory analysis of unknowns, trace analysis and non-routine work

(such as peak interferences).

This document is applicable to EPMA and other wavelength dispersive spectrometer (WDS) systems in

which elemental identification and quantification are performed by analysis of the energy and intensity

of the characteristic X-ray lines observed in wavelength-dispersed X-ray spectra. It is not directly

applicable to elemental analysis using energy dispersive spectrometry (EDS).
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 3534-2, Statistics — Vocabulary and symbols — Part 2: Applied statistics

ISO 14595, Microbeam analysis — Electron probe microanalysis — Guidelines for the specification of

certified reference materials (CRMs)

ISO 22489, Microbeam analysis — Electron probe microanalysis — Quantitative point analysis for bulk

specimens using wavelength dispersive X-ray spectroscopy
ISO 23833, Microbeam analysis — Electron probe microanalysis (EPMA) — Vocabulary

ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated

terms (VIM)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/IEC Guide 99, ISO 3534-2,

ISO 23833 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/
© ISO 2018 – All rights reserved 1
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ISO 19463:2018(E)
3.1
electron probe microanalyser
EPMA
instrument for carrying out electron-excited X-ray microanalysis

Note 1 to entry: This instrument is usually equipped with more than one wavelength spectrometer and an optical

microscope for precise specimen placement.
[SOURCE: ISO 23833:2013, 3.2]
3.1.1
electron probe microanalysis
EPMA

technique of spatially-resolved elemental analysis based upon electron-excited X-ray spectrometry

with a focussed electron probe and an electron interaction volume with micrometer to sub-micrometer

dimensions
[SOURCE: ISO 23833:2013, 3.1]
3.2
wavelength dispersive spectrometer
WDS

device for determining X-ray intensity as a function of the wavelength of the radiation, where separation

is based upon Bragg's law, nλ = 2dsinθ, where n is an integer, λ is the X-ray wavelength, d is the spacing

of the atom planes of the diffracting crystal or the repeated layers of a synthetic diffractor and θ is the

angle at which constructive interference takes place

Note 1 to entry: This definition excludes the recent technological development of WDS spectrometers based on

diffraction at gratings, which are not as yet in widespread use.
[SOURCE: ISO 23833:2013, 4.6.14, modified — Note 1 to entry replaced.]
3.3
diffracting crystal
dispersion element

X-ray scattering element in a wavelength-dispersive X-ray spectrometer, consisting of a periodic array

of atoms obtained either in a natural crystal or in a synthetic multilayer

Note 1 to entry: For the purposes of this document, the term “diffracting crystal” is used rather than the term

“dispersion element” in order to avoid confusion when discussion of components of X-ray energy analysers is

intermingled with discussion of chemical elements from the periodic table.
[SOURCE: ISO 23833:2013, 4.6.14.3, modified — Note 1 to entry has been added.]
3.3.1
lithium fluoride
LiF
[4]

diffracting crystal featuring 2d spacing of 0,402 8 nm used in WDS for dispersion of X-rays

Note 1 to entry: This can also sometimes be written as LiF(200) to denote the most common crystallographic

orientation of LiF used. However, it is also available in other less commonly used orientations that feature

different 2d spacings; for example, the [220] orientation has a 2d spacing of 0,284 8 nm. Additionally, some

instruments could utilize LiF in the [422] or the [420] orientation. If the orientation is not stated, the [200]

orientation is assumed. All orientations are typically used to disperse short wavelength/high energy X-rays.

3.3.2
pentaerythritol
PET
[4]

diffracting crystal featuring 2d spacing of 0,874 2 nm used in WDS for dispersion of X-rays

Note 1 to entry: PET is typically used to disperse intermediate wavelength/intermediate energy X-rays.

2 © ISO 2018 – All rights reserved
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ISO 19463:2018(E)
3.3.3
thallium acid phthalate
TAP
[4]

diffracting crystal featuring 2d spacing of 2,59 nm used in WDS for dispersion of X-rays

Note 1 to entry: TAP is typically used to disperse long wavelength/low energy X-rays.

3.3.4
layered synthetic microstructure

multilayer diffracting element engineered to feature an arbitrary 2d spacing used in WDS for dispersion

of X-rays

Note 1 to entry: layered synthetic microstructure is typically used to disperse long wavelength/low energy

X-rays in the light element region of the spectrum inaccessible by TAP.
3.4
peak energy
peak wavelength

spectrometer position or channel at which the characteristic peak intensity is measured

Note 1 to entry: Due to X-ray counts originating from higher-order Bragg reflections, both of these terms

describe the measurand but not the actual measurement; an EPMA instrument counts X-rays from the higher-

order reflections and the principle first-order reflection simultaneously. Pulse filtering electronics can be used

to preferentially distinguish X-rays at the wavelength or energy of interest; in practice, such strategies reduce

but do not eliminate spurious counts.
3.5
peak counting time
time spent measuring X-ray emission at a given characteristic peak energy
3.6
peak counting rate

mean rate at which characteristic peak X-rays are collected by the detector at the peak energy

3.7
background reference
background reference energy
background reference wavelength

spectrometer position or channel at which the continuous background radiation is measured so that

an estimate can be made of what portion of the measured intensity at a characteristic peak originates

from characteristic photoemission

Note 1 to entry: Multiple background positions are typically chosen to improve the estimate; often, at least one

on each side of the characteristic peak of interest.

Note 2 to entry: Due to X-ray counts originating from higher-order Bragg reflections, both of these terms

describe the measurand but not the actual measurement; an EPMA instrument counts X-rays from the higher-

order reflections and the principle first-order reflection simultaneously. Pulse-filtering electronics can be used

to preferentially distinguish X-rays at the wavelength or energy of interest; in practice, such strategies reduce

but do not eliminate spurious counts.
3.8
background counting time
time spent measuring X-ray emission at a given background energy
3.9
background counting rate

mean rate at which continuum X-rays are collected by the detector at the background energy

Note 1 to entry: The background counting rate is used to estimate the portion of peak counts due to continuum

X-rays; this estimate may be derived by interpolation, extrapolation, or comparison to the background rate

generated by a selection of materials characterized by a range of mean atomic numbers.

© ISO 2018 – All rights reserved 3
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ISO 19463:2018(E)
3.10
beam defocus

condition in which the objective lens of the electron optical column is set such that the size of the

incidence of the electron beam on the surface of the specimen (the “beam spot”) is expanded to a

diameter greater than the diameter of the focal point

Note 1 to entry: Increasing the spot size is a technique used to compensate for specimen heterogeneity when

performing a quantitative analysis or to reduce the damage caused to a beam-sensitive specimen by distributing

the electron dose over a greater volume.
3.11
quality assurance

procedure by which standard measurements of model materials are

performed on a periodic basis to confirm that each component of the electron probe microanalyser is

functioning such that the instrument’s uncertainty specification is attainable
3.12
confidence interval

range of analytical error expected to contain the true value with a stated uncertainty as estimated

from a statistical model of the measurement process
[SOURCE: ISO 23833:2013, 5.4.2.1]
3.13
error

natural deviation from the true value in a measured quantity arising from (1) random counting

fluctuations in a time-distributed phenomenon (e.g. X-ray photons) and (2) systematic deviations

from the true value introduced during application of calculated correction factors (e.g. ZAF matrix

correction factors) to convert the measured quantity (e.g. X-ray photons) to a different dimension (e.g.

concentration)
[SOURCE: ISO 23833:2013, 5.4.2]
3.14
uncertainty

quantitative statement that provides a value for the expected deviation of a measurement from an

estimate of the value of the specific measured quantity
[SOURCE: ISO 23833:2013, 5.5.13]
3.15
detection limit

smallest amount of an element or compound that can be measured under specific analysis conditions

Note 1 to entry: By convention, the detection limit is often taken to correspond to the amount of material for

which the total signal for that material minus the background signal is three times the standard deviation of the

signal above the background signal. This convention might not be applicable to all measurements and, for a fuller

discussion of detection limits, Reference [11] should be consulted.

Note 2 to entry: The detection limit may be expressed in many ways depending on the purpose. Examples of

expressions are mass or weight fraction, atomic fraction, concentration, number of atoms, and mass or weight.

Note 3 to entry: The detection limit will generally be different for different materials.

[SOURCE: ISO 23833:2013, 5.2]
3.16
instrument uncertainty specification

manufacturer’s estimate of the lowest uncertainty attainable by a

given instrument based upon physical limitations and construction
4 © ISO 2018 – All rights reserved
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ISO 19463:2018(E)
3.17
control chart

chart on which some statistical measure of a series of samples is plotted in a particular order to steer

the process with respect to that measure and to control and reduce variation

[SOURCE: ISO 3534-2:2006, 2.3.1, modified — Notes 1 and 2 to entry have been removed.]

3.17.1
mean and standard deviation plot
mean and range plot
x̅ and R plot

graphical representation of a set of measurements that plots the data means in relation to a certified or

targeted value and also plots the standard deviations in relation to a control limit

Note 1 to entry: Mean and standard deviation plots can be used as an aid in determining when and how the data

no longer attains the instrument uncertainty specification.
3.17.2
box-and-whisker plot
box plot

graphical representation of a set of measurements that plots the data along with the data mean, median,

inner quartiles (“box”) and a chosen outlier delimiter (e.g. standard deviation, outer quartiles or other

“whiskers”)

Note 1 to entry: Box plots can be used as an aid in determining when and how the data no longer attains the

instrument uncertainty specification.
3.17.3
bean plot
density plot

graphical representation of a set of measurements that plots the data along with the data mean and a

density function

Note 1 to entry: Bean plots can be used as an aid in determining when and how the data no longer conforms to

the instrument uncertainty specification.
3.18
failure mode

observable deviation from a normal data distribution within the

instrument uncertainty specification that is symptomatic of a specific instrument malfunction

3.19
reference material

material, sufficiently homogeneous and stable with reference to specified properties, which has been

established to be fit for its intended use in measurement or in examination of nominal properties

Note 1 to entry: For electron probe microanalysis, a material whose overall composition is known from

independent, ideally absolute, measurements (e.g. separations and gravimetric analysis) and that is

microscopically homogeneous on a sufficiently fine scale that any location measured with an electron probe

microanalyser produces the same X-ray intensities, within counting statistics.

[SOURCE: ISO/IEC Guide 99:2007, 5.13, modified — Note 1 to entry has been added.]

© ISO 2018 – All rights reserved 5
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ISO 19463:2018(E)
3.19.1
certified reference material
CRM

reference material (3.19)accompanied by documentation issued by an authoritative body and providing

one or more specified property values with associated uncertainties and traceabilities, using valid

procedures

Note 1 to entry: For certified reference materials for electron probe microanalysis, the microscopic heterogeneity

at the micrometer scale is certified as well as the composition.

[SOURCE: ISO/IEC Guide 99:2007, 5.14, modified — Note 1 to entry has been added.]

3.19.1.1
challenge material

certified reference material (3.19.1) of known composition that is measured as if it were an unknown

sample in the EPMA QA procedure

Note 1 to entry: Challenge materials are selected by the analyst to present an analytical challenge to specific

components of an EPMA instrument. Ideally, challenge materials that present an analytical challenge to as many

components of a given instrument as possible should be selected.
4 General principles of electron probe microanalyser quality assurance
(EPMA QA)
4.1 Objective

When performing analysis of unknown specimens in EPMA, it is crucial for the analyst to know that

their instrument is working properly. Herein is described a procedure that should be performed

periodically to ensure that analyses performed using EPMA are reliable. The procedure is built upon

the analysis of challenge materials.
4.2 Selection of challenge materials
4.2.1 General

Challenge materials and their associated reference materials shall be selected such that they conform

to the criteria outlined in the following subsections.
4.2.2 General characteristics of analysed materials

Challenge materials and their associated reference materials shall meet the requirements for certified

reference materials as described in ISO 14595. The materials shall:
a) be stable in vacuum;
b) not degrade under interrogation by the electron beam incidence;

c) be characterized by heterogeneity sufficiently less than the instrument’s repeatability specification

so as to be indistinguishable from the instrument uncertainty specification;

d) be suitably conductive to eliminate electrostatic charging under electron beam interrogation (or be

coated with conductive material with a path to instrument ground);

Many types of solids meet these criteria, including a number of pure elemental solids, single-phase

alloys, vitreous solids such as glass, natural or synthetic minerals, and pure compounds.

6 © ISO 2018 – All rights reserved
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ISO 19463:2018(E)
4.2.3 Specific characteristics of challenge materials

The purpose of a challenge material is to provide an analytical challenge for an instrument that

requires the proper function of as many instrument components as possible. Therefore, a challenge

material should be sufficiently complex such that each diffracting crystal on every WDS in a given

EPMA can be used to quantify at least one of the elements of which it is composed. For multi-crystal

WDS spectrometers, diffracting crystal switching should be required.

The challenge material should also be sufficiently simple to analyse such that deconvolution of peak

overlaps and large absorption or fluorescence corrections are not required to calculate the composition.

Secondary standard reference materials should not be necessary to achieve an accurate result. Finally,

the elements of interest for evaluating the performance of a given spectrometer should be present

...

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