ASTM E1621-22

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1621 − 21 E1621 − 22
Standard Guide for
Elemental Analysis by Wavelength Dispersive X-Ray
Fluorescence Spectrometry
This standard is issued under the fixed designation E1621; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guidestandard provides guidelines for developing and describing analytical procedures using a wavelength dispersive
X-ray spectrometer for elemental analysis of solid metals, ores, and related materials. Material forms discussed herein include
solids, powders, and solid forms prepared by chemical and physical processes such as borate fusion and pressing of briquettes.
1.2 Liquids are not discussed in this guide because they are much less frequently encountered in metals and mining laboratories.
However, aqueous liquids can be processed by borate fusion to create solid specimens, and X-ray spectrometers can be equipped
to handle liquids directly.
1.3 Some provisions of this guide may be applicable to the use of an energy dispersive X-ray spectrometer.
1.4 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E1257 Guide for Evaluating Grinding Materials Used for Surface Preparation in Spectrochemical Analysis
E1329 Practice for Verification and Use of Control Charts in Spectrochemical Analysis (Withdrawn 2019)
E1361 Guide for Correction of Interelement Effects in X-Ray Spectrometric Analysis
E2857 Guide for Validating Analytical Methods
This guide is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Subcommittee E01.20 on Fundamental Practices.
Current edition approved May 15, 2021June 15, 2022. Published June 2021July 2022. Originally approved in 1994. Last previous edition approved in 20132021 as
E1621 – 13.E1621 – 21. DOI: 10.1520/E1621-21.10.1520/E1621-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1621 − 22
E2972 Guide for Production, Testing, and Value Assignment of In-House Reference Materials for Metals, Ores, and Other
Related Materials
2.2 ISO Standard:
ISO 17034: 2016 General Requirements for the Competence of Reference Material Producers
3. Terminology
3.1 Definitions—For definitions of terms used in this guide, refer to TerminologiesTerminology E135 and the terminology
section of Guide E1361.
4. Summary of Guide
4.1 Important aspects of test equipment for wavelength dispersive X-ray fluorescence spectrometry are discussed including
equipment components and accessories, reagents, and materials. Key aspects of the application of X-ray spectrometry to materials
analysis are discussed including interferences and correction options, specimen preparation by a variety of procedures, and
materials and accessories for presentation of specimens for measurement in spectrometers. Key elements of measurement
procedures, calibrationscalibration procedures, and result reporting are explained.
4.2 In an X-ray spectrometric test method, the test specimen is prepared with a clean, uniform, flat surface. It may be prepared
by grinding, polishing, or lathing a metal surface or by fusing or briquetting a powder. This surface is irradiated with a primary
source of X-rays. The secondary X-rays produced in the specimen are dispersed according to their wavelengths by means of
crystals or synthetic multilayers. Their count rates at selected wavelengths, hereinafter called intensities, are measured by suitable
detector systems. Amounts of the elements are determined from the measured intensities using analytical curves calibrations
prepared with suitable calibrants.
4.3 Important aspects of background estimation are covered in Appendix X1an appendix to the guide.
5. Significance and Use
5.1 X-ray fluorescence spectrometry can provide an accurate determination of metallic and many non-metallic elements in a wide
variety of solid and liquid materials. This guide covers the information that should be included in an X-ray spectrometric analytical
method and provides direction to the analystuser for determining the optimum conditions needed to achieve acceptable accuracy.
5.2 The accuracy of a determination is a function of the calibration scheme,algorithm, the sample preparation, and the sample
homogeneity. Close attention to all aspects of these areas is necessary to achieve acceptable results.
5.3 All concepts discussed in this guide are explored in detail in a number of published texts and in the scientific literature.
6. Interferences
6.1 Line overlaps, either total or partial, may occur for some elements. If sufficient sensitivity exists, it may be possible to reduce
or eliminate the overlap by choosing a higher level of collimation in the secondary X-ray path from specimen to dispersive element
or detector. See Appendix X1 for optional approaches to the correction of line overlap effects.
6.1.1 Fundamental parameter (FP) equations require net intensities with background subtraction and line overlap corrections
performed before the FP calculations are carried out. conducted. Some empirical schemesalgorithms incorporate line overlap
corrections in their equations, and some software allows combinations of empirical and FP calculations chosen by element or other
analyte.
6.1.2 In addition, line overlap interferences may occur from characteristic lines generated from the target material of the X-ray
tube and scattered from the specimen either inelastically (known as Compton scatter) or elastically (known as Rayleigh scatter).
These may be reduced or eliminated by the use of using primary beam filters, with a consequent loss of sensitivity.
6.2 Interelement effects (sometimes called matrix effects, see Note 16.2.2) may be significant for some elements. An empirical way
Available from International Organization for Standardization (ISO), ISO Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland,
https://www.iso.org.
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to compensate for these effects is to prepare a series of calibration curves calibrations that cover the designated mass fraction ranges
to be analyzed. Typically, more accurate results are obtained when the compositions of the calibrants used to prepare the particular
calibration curves calibrations are similar to the compositions of materials being analyzed. This approach requires many more
standards reference materials (RMs) than more modern methods, and this approach is generally superseded by mathematical
methods.
6.2.1 Alternatively, mathematical methods may be used to compensate for interelement or matrix effects. Various mathematical
correction procedures are commonly utilized. See Guide E1361. Any of these that will achieve the necessary analytical accuracy
is acceptable.
6.2.2 Alternatively, mathematical methods may be used to compensate for interelement or matrix effects. Various mathematical
correction procedures are commonly utilized. See GuideInterelement effects are not interferences in the spectrometric sense but
will contribute to errors in the analysis if not properly addressed. Interelement E1361. Any of these that will achieve the necessary
analytical accuracy is acceptable. effects result from the absorption of X-rays to differing extents by the atoms in the specimen
according to the mass absorption coefficient. Use caution with empirical mathematical models to ensure that sufficient data are
provided to adequately compensate for these effects.
NOTE 1—Interelement effects are not interferences in the spectrometric sense, but will contribute to errors in the analysis if not properly addressed.
Interelement effects result from the absorption of X-rays to differing extents by the atoms in the specimen according to the mass absorption coefficient.
Caution must be used with empirical mathematical models to be sure that sufficient data are provided to adequately compensate for these effects.
6.3 Errors From Metallurgical Structure—Because the analyte intensity is affected by the mass absorption of the sample and
mathematical models assume a homogeneous sample, a bias may result if the analyte exists in a separate phase, such as an
inclusion. For example, in a steel that contains carbon and carbide formers such as titanium and niobium, the titanium may exist
in a titanium-niobium carbide that has a lower mass absorption coefficient than iron for the titanium K-L (Kα) line. The intensity
2,3
for titanium is higher in this sample than it would be if the titanium, niobium, carbon, and iron were always in solid solution.
7. Apparatus
7.1 Specimen Preparation Equipment for Solid Metals:
7.1.1 Surface Grinder or Sander With Abrasive Belts or Disks, or Lathe, or Mill capable of providing a flat, uniform surface on
both the reference materials and test specimens.
7.1.1.1 Abrasive disks are preferred over belts because the platen on a belt sandergrinder tends to wear and produce a convex
surface on the specimen. If belt sandersgrinders are used, care must be exercised to be sure exercise care to ensure the platen is
maintained flat.
7.1.1.2 The grinding materialmedia should be selected so no significant contamination occurs for the elements of interest during
the sample preparation. (Refer to Guide E1257.)
7.1.1.3 Grinding belts or disks shall be changed at regular, specified intervals because abrasives lose their ability to remove
material efficiently and without inducing contamination. This is particularly important in alloys that exhibit smearing of a softer
component across the surface.
7.1.1.4 Provision of flowing water across the surface of a grinding wheel belt or disk cools the specimen and removes debris.
Chemical coolants, such as those used in machine shops, should not be used, except for special purposes.
7.1.1.5 The use of a lathe, or similar type of machine, is recommended for soft metals or metals that have components that can
smear when surfaced with an abrasive disk.media. The feed on the cutting tools should be constant, and automatically controlled,
to give a consistent finish.
7.2 Specimen Preparation Equipment for Powders:
7.2.1 Jaw Crusher or Steel Mortar and Pestle, for initial crushing of larger chunks of material.
7.2.2 Plate Grinder or Pulverizer, with one static and one rotating disk for further grinding or crushing.
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7.2.3 Rotary Disk Mill or Swing Mill, with hardened grinding containers and timer control for final grinding.
7.2.4 Briquetting Press, providing pressures of up to 550 MPa. The press shall be equipped with a mold assembly that provides
a briquette that is compatible with the X-ray specimen holder.
7.2.5 Fusion Equipment, with a timer, capable of heating the sample and flux to at least 975 °C and homogenizing the melt.
7.2.6 Fusion Crucibles, compatible with the flux and sample type:
7.2.6.1 Vitreous Carbon, flat bottomed with a suitable diameter and capacity to produce a fused disk compatible with the X-ray
specimen holder.
7.2.6.2 95 % Platinum/5 % Gold Alloy, with a suitable capacity for the casting molds being employed.
7.2.7 Platinum/Gold Casting Mold (95 % ⁄5 %), having a flat, optical-polished bottom and sufficient capacity to hold the quantity
of glass needed to make a cast bead of roughlynearly uniform thickness across the entire diameter, typically 30 mm to 40 mm.
7.2.8 Polishing Wheel, suitable for polishing the fused bead to obtain a flat uniform surface for irradiation. For machines that cast
a bead in a polished dish, this step may not be necessary.
7.3 Excitation Source:
7.3.1 X-Ray Tubes, with targets of various high-purity elements that are capable of continuous operation at potentials and currents
that will excite the elements to be determined.
7.3.2 X-Ray Tube Power Supply, providing a stable voltage of sufficient energy to produce secondary radiation from the specimen
for the elements specified. The instrument may be equipped with an external line voltage regulator or a transient voltage suppressor.
7.3.3 The instrument may be equipped with an external line voltage regulator or a transient voltage suppressor.
7.4 Spectrometer, designed for X-ray fluorescence analysis, and equipped with specimen holders and a specimen chamber. The
chamber may contain a specimen spinner,spinner and must be equipped for vacuum or helium-flushed operation for the
determination of elements of atomic number 20 (calcium) or lower.
7.4.1 Analyzing Crystals, flat or curved crystals with optimized capability for the diffraction of the wavelengths of interest. The
term is also applied to synthetic multi-layer structures that are preferred for some applications.
7.4.2 Collimator, for limiting the characteristic X-rays to a parallel bundle when flat crystals are used in the instrument. For
longitudinally curved crystal optics, a collimator is not necessary, and may be replaced by entrance and exit slits.
7.4.3 Masks, for restricting the portion of the specimen viewed by the collimator or entrance slit.
7.4.4 Detectors—Detectors, Sealedsealed or gas-flow proportional counters and scintillation counters are most commonly used.
Tandem configurations are available to allow simultaneous use of two detectors.
7.4.5 Vacuum System, for the determination of elements whose radiation is absorbed to a significant extent by air. The system shall
consist of a vacuum pump, gauge, and electrical controls to provide automatic pumpdownevacuation of the optical path, and
maintain a controlled pressure, usually 13 Pa (100 μm Hg) or less.
7.5 Measuring System, consisting of electronic circuits capable of amplifying and shaping pulses received from the detectors. The
system shall be equipped with an appropriate data output device.
7.5.1 Pulse Height Selectors, used to discriminate against pulses from higher order X-ray lines and background.
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8. Reagents and Materials
8.1 Purity of Reagents—Reagents used in X-ray fluorescence test methods must be evaluated for appropriate purity for the stated
purpose and the expected performance of the test method.
8.2 Binder—One of a wide variety of compounds or materials that provide cohesion of particles in a briquette including
polyethylene glycol, cellulose, spectrographic grade graphite (<74 μm briquetting type), borate compounds, and other chemicals.
8.3 Detector Gas—Typical detector gas consists of a mixture of 90 % argon and 10 % methane for use with gas-flow proportional
counters. Other gases are used to enhance sensitivity over selected wavelength ranges.
8.4 Fluxes—Lithium tetraborate (Li B O ), lithium metaborate (LiBO ), mixtures of tetraborate and metaborate, boric anhydrite
2 4 7 2
(B O ), and sodium tetraborate (Na B O ). Pre-fused versions of the borate fluxes are available in high-purity versions, some of
2 3 2 4 7
which are mixed with halide compound non-wetting releasing (non-wetting) agents, fluidizers, and heavy absorbers, for example,
lanthanum oxide. There may be additional flux compositions suitable for dissolution of samples.
9. Reference Materials
9.1 Certified Reference Materials are available from national metrology institutes and from private and public organizations that
certify reference materials for chemical composition in accordance with ISO 17034 and with relevant supplemental standards and
guidelines implemented by standards development organizations concerned with a particular business sector.
9.2 Reference Materials with matrix compositions similar to that of the test specimen and containing varying amounts of the
elements to be determined may be used, provided they have been analyzed in accordance with validated test methods. These
reference materials should be sufficiently homogeneous for the intended purpose. See Guide E2972.
9.3 The reference materials should cover the composition mass fraction ranges of the elements being determined. An appropriate
number of reference materials shall be used for each element, depending on the mathematical models being used.
10. Hazards
10.1 Exposure to excessive quantities of high energy radiation such as those produced by X-ray spectrometers is injurious to
health. The operator should take appropriate actions to avoid exposing any part of their body to primary X-rays, primary,
secondary, and scattered X-radiationX-rays that may be present. The X-ray spectrometer should be operated in accordance with
regulations governing the use of ionizing radiation. Manufacturers of X-ray fluorescence spectrometers typically buildinstall
appropriate shielding and safety interlocks into X-ray equipment during manufacturing, in X-ray spectrometers, which minimize
the risk of excessive radiation exposure to operators. Operators should not attempt to bypass or defeat safety devices. Only
authorized personnel should service X-ray spectrometers.
10.2 Monitoring Devices, such as film badges or dosimeters may be used by operators and maintainers. service personnel. Periodic
radiation surveys of the equipment for leaks and excessive scattered radiation may be required by governing laws or regulations.
11. Preparation of Reference Materials and Test Specimens
11.1 Throughout the procedure, treat reference materials and test specimens exactly the same way. Consistency in preparation of
reference materials and specimens is essential to ensure reproducible results. After the preparation procedure is established, it must
be followed exactly. Variations in technique, such as grinding time, abrasive grit size or material, particle size, binder material,
sample-binder ratio, briquetting pressure, or holding times, can cause unreliable results.
11.2 Solid Metal Samples—Prepare the reference materials and test specimens so that each has a clean, flat uniform surface to be
exposed to the X-ray beam. For abrasive sanding,grinding, select a final grit size and use it exclusively for all reference materials
and test specimens. Several coarser grits may be needed before the final grit can be used. Choose the final grit small enough to
minimize the effects of grinding striations on measured intensity. See Note 211.2.1 and 7.1. Refinish the surface of the reference
materials and test specimens using the same batches of all grit papersgrinding media on all specimens, even if some samples were
previously finished with the same grit,media, but of a different batch.
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NOTE 2—The final grit size should be small enough to minimize shadowing effects in which X-rays are absorbed by the raised portions of metal on either
side of the grooves created by grinding. To check for problems, place a prepared specimen in the X-ray spectrometer with the grinding marks parallel
to the optical path and with spinning disabled. Measure the intensities of all elements. Then, move the specimen so the grinding marks are perpendicular
to the optical path and measure again. If the intensities of any elements decrease significantly, there is grinding-induced absorption. During measurements,
spinning of all specimens may prevent the effects from causing biases.
11.2.1 The final grit size should be small enough to minimize shadowing effects in which X-rays are absorbed by the raised
portions of metal on either side of the grooves created by grinding. To check for problems, place a prepared specimen in the X-ray
spectrometer with the grinding marks parallel to the optical path and with spinning disabled. Measure the intensities of all
elements. Then, move the specimen so the grinding marks are perpendicular to the optical path and measure again. If the intensities
of any elements decrease significantly, there is grinding-induced absorption. During measurements, spinning of all specimens may
prevent the effects from causing biases.
11.3 Nonmetallic Samples—Dry the material. Then reduce it both in particle size and quantity, for example, by crushing and
pulverizing followed by splitting or riffling, ending with approximately 100 g of material that has a particle size distribution with
a maximum of 74 μm (200 mesh).
11.3.1 Briquettes—Mix the sample with a suitable binder if required. (See 8.2.) Ratios of 10 g + 1 g to 20 g + 1 g of
sample + binder are common. Grind and blend the sample and binder for a fixed time (generally 2 min to 4 min in a disk mill).
Press the sample-binder mixture into a briquette using a fixed pressure (typical pressures are between 140 MPa to 550 MPa) and
maintaining the pressure for a minimum of 10 s before releasing the briquette. In some cases, holding the pressure at 140 MPa
for about 10 s before increasing it to maximum or pumpingapplying a vacuum on the side port of a die set allows air to escape
from the mixture and reduces the possibility of the briquette bursting from internal pressure. The exact conditions for pressing
briquettes are either prescribed in the method,method or determined experimentally.
NOTE 1—For some samples, an aluminum or plastic pressing cup may be required to support the briquette.
11.3.2 Fused Beads—Develop and apply a fusion procedure that is appropriate for the matrix and elements of interest. Automated
fusion equipment is readily available from several suppliers. Use a predetermined ratio of sample to flux. For example, 1.0 g of
sample plus 4.0 g to 10.0 g of mixed lithium borate fluxes are commonly used. Mix weighed amounts of sample and flux,flux and
place the mixture in clean platinum/gold. platinum/gold crucible. Heat at a fixed temperature, usually from 950975 °C to 1100 °C,
until thoroughly melted. Mix the crucible contents to ensure a homogeneous fusion and to remove particles from the crucible walls.
Fusion time may vary from, for example, from 2 min to 10 min, or more, depending on the sample, flux, and sample to flux ratio.
(Warning—Ensure the sample is completely oxidized prior to fusing with the flux. Un-oxidized metals may alloy with the
platinum/gold crucible and destroy it.)
11.3.2.1 When using platinum/gold crucibles, cast the fused mixture into a preheated platinum/gold mold, and allow to solidify
and cool in the mold. Remove the bead.
11.3.2.2 For many applications, analysis of the as-cast surface of the bead may be adequate. This demands that the bottom of the
casting dish is flat and free from scratches. Each laboratory must determine if polishing is e
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