ASTM E2926-13
(Test Method)Standard Test Method for Forensic Comparison of Glass Using Micro X-ray Fluorescence (µ-XRF) Spectrometry
Standard Test Method for Forensic Comparison of Glass Using Micro X-ray Fluorescence (µ-XRF) Spectrometry
SIGNIFICANCE AND USE
4.1 µ-XRF provides a means of simultaneously detecting major, minor, and trace elemental constituents in small glass fragments such as those frequently examined in forensic case work. It can be used at any point in the analytical scheme without concern for changing sample shape or sample properties, such as RI, due to its totally nondestructive nature.
4.2 Limits of detection (LOD) are dependent on several factors, including instrument configuration and operating parameters, sample thickness, and atomic number of the individual elements. Typical LODs range from parts per million (µgg-1) to percent (%).
4.3 µ-XRF provides simultaneous qualitative analysis for elements having an atomic number of eleven or greater. This multi-element capability permits detection of elements typically present in glass such as magnesium (Mg), silicon (Si), aluminum (Al), calcium (Ca), potassium (K), iron (Fe), titanium (Ti), strontium (Sr), and zirconium (Zr), as well as other elements that may be detectable in some glass by µ-XRF (for example, molybdenum (Mo), selenium (Se), or erbium (Er)) without the need for a predetermined elemental menu.
4.4 µ-XRF comparison of glass fragments provides additional discrimination power beyond that of RI or density comparisons, or both, alone.
4.5 The method precision should be established in each laboratory for the specific conditions and instrumentation in that laboratory.
4.6 When using small fragments having varying surface geometries and thicknesses, precision deteriorates due to take-off-angle and critical depth effects. Flat fragments with thickness greater than 1.5 mm do not suffer from these constraints, but are not always available as questioned specimens received in casework. As a consequence of the deterioration in precision for small fragments and the lack of appropriate calibration standards, quantitative analysis by µ-XRF is not typically used.
4.7 Appropriate sampling techniques should be used to account for natural...
SCOPE
1.1 This test method is for the determination of major, minor, and trace elements present in glass fragments. The elemental composition of a glass fragment can be measured through the use of µ-XRF analysis for comparisons of glass.
1.2 This test method covers the application of µ-XRF using mono- and poly- capillary optics, and an energy dispersive X-ray detector (EDS).
1.3 This test method does not replace knowledge, skill, ability, experience, education, or training and should be used in conjunction with professional judgment.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2926 − 13
Standard Test Method for
Forensic Comparison of Glass Using Micro X-ray
Fluorescence (µ-XRF) Spectrometry
This standard is issued under the fixed designation E2926; 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.
INTRODUCTION
One objective of a forensic glass examination is to compare glass specimens to determine if they
canbediscriminatedusingtheirphysical,opticalorchemicalproperties(forexample,color,refractive
index (RI), density, elemental composition). If the specimens are distinguishable, except for
acceptable and explainable variations, in any of these observed and measured properties, it may be
concluded that they did not originate from the same source of broken glass. If the specimens are
indistinguishable in all of these observed and measured properties, the possibility that they originated
from the same source of glass cannot be eliminated. The use of an elemental analysis method such as
micro X-ray fluorescence spectrometry (µ-XRF) yields high discrimination among sources of glass.
1. Scope E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
1.1 This test method is for the determination of major,
E2330 Test Method for Determination of Concentrations of
minor, and trace elements present in glass fragments. The
Elements in Glass Samples Using Inductively Coupled
elemental composition of a glass fragment can be measured
Plasma Mass Spectrometry (ICP-MS) for Forensic Com-
through the use of µ-XRF analysis for comparisons of glass.
parisons
1.2 This test method covers the application of µ-XRF using
mono- and poly- capillary optics, and an energy dispersive
3. Summary of Test Method
X-ray detector (EDS).
3.1 µ-XRF is a nondestructive elemental analysis technique
1.3 This test method does not replace knowledge, skill,
based on the emission of characteristic X-rays following the
ability,experience,education,ortrainingandshouldbeusedin
excitation of the specimen by an X-ray source using capillary
conjunction with professional judgment.
optics. Simultaneous multi-elemental analysis is typically
achieved for elements of atomic number eleven or greater.
1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3.2 Glass fragments usually do not require sample prepara-
standard.
tion prior to analysis by µ-XRF. Cleaning of specimens may be
1.5 This standard does not purport to address all of the performed to remove any surface debris.
safety concerns, if any, associated with its use. It is the
3.3 Specimens are mounted and placed into the instrument
responsibility of the user of this standard to establish appro-
chamber and subjected to an X-ray beam. The characteristic
priate safety and health practices and determine the applica-
X-rays emitted by the specimen are detected using an energy
bility of regulatory limitations prior to use.
dispersive X-ray detector and displayed as a spectrum of
energy versus intensity.
2. Referenced Documents
3.4 Qualitative analysis is accomplished by identifying
2.1 ASTM Standards:
elements present in the specimen based on their characteristic
X-ray energies.
ThistestmethodisunderthejurisdictionofASTMCommitteeE30onForensic
3.5 Semi-quantitative analysis is accomplished by compar-
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
ing the relative area under the peaks of characteristic X-rays of
Current edition approved June 15, 2013. Published July 2013. DOI: 10.1520/
certain elements.
E2926-13.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.6 Spectral and elemental ratio comparisons of the glass
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
specimens are conducted for source discrimination or associa-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. tion.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2926 − 13
4. Significance and Use trace concentration levels. However, discrimination of sources
that have indistinguishable RIs and densities may be possible.
4.1 µ-XRF provides a means of simultaneously detecting
major, minor, and trace elemental constituents in small glass
5. Interferences
fragments such as those frequently examined in forensic case
work. It can be used at any point in the analytical scheme
5.1 Peak overlaps occur in various regions of the EDS
without concern for changing sample shape or sample
spectrum. In glass, such interferences include the overlap of
properties, such as RI, due to its totally nondestructive nature.
characteristic X-ray lines (for example, Ti K-series and Ba
L-series), sum peaks, primary X-ray source excitation peaks
4.2 Limits of detection (LOD) are dependent on several
(for example, Rh), and escape peaks. In general, automated
factors, including instrument configuration and operating
deconvolution algorithms are included in data processing
parameters, sample thickness, and atomic number of the
software that adequately address such overlaps. EDS spectra
individual elements. Typical LODs range from parts per
-1 shall be manually inspected to ensure that potential peak
million (µgg ) to percent (%).
overlaps are considered and addressed.
4.3 µ-XRF provides simultaneous qualitative analysis for
elements having an atomic number of eleven or greater. This
6. Apparatus
multi-element capability permits detection of elements typi-
6.1 A µ-XRF spectrometer with an EDS detector is em-
cally present in glass such as magnesium (Mg), silicon (Si),
ployed. Most commercial-grade µ-XRF systems with EDS
aluminum (Al), calcium (Ca), potassium (K), iron (Fe), tita-
detectors should be adequate for forensic analysis of glass.The
nium (Ti), strontium (Sr), and zirconium (Zr), as well as other
µ-XRFsystemmust,however,meetthefollowingperformance
elements that may be detectable in some glass by µ-XRF (for
specifications:
example, molybdenum (Mo), selenium (Se), or erbium (Er))
6.1.1 The spot size(s) must be within the range(s) of
without the need for a predetermined elemental menu.
approximately 10 µm to 2 mm; the spot size used may be
4.4 µ-XRF comparison of glass fragments provides addi-
adjustable to different sizing for instruments with appropriate
tional discrimination power beyond that of RI or density
optics.
comparisons, or both, alone.
6.1.2 The instrument must be capable of operating at an
4.5 The method precision should be established in each
accelerating voltage of 35 kV or greater.
laboratory for the specific conditions and instrumentation in
6.1.3 The EDS detector must be capable of a resolution that
that laboratory.
is typically less than 180 eV, measured as the full width at half
themaximumheightoftheMnKαpeak;betterresolutionswill
4.6 When using small fragments having varying surface
provide improved discrimination of adjacent or overlapping
geometries and thicknesses, precision deteriorates due to take-
peaks, or both.
off-angle and critical depth effects. Flat fragments with thick-
6.1.4 Acalibrated, scaled display of energy units (keV) and
ness greater than 1.5 mm do not suffer from these constraints,
the ability to identify and label X-ray lines is required for the
but are not always available as questioned specimens received
EDS system.
incasework.Asaconsequenceofthedeteriorationinprecision
for small fragments and the lack of appropriate calibration
6.2 Energy Calibration Material—Capable of calibrating
standards,quantitativeanalysisbyµ-XRFisnottypicallyused.
the EDS detector at both the low (<2 keV) and high (>6 keV)
X-ray spectral regions.
4.7 Appropriate sampling techniques should be used to
account for natural heterogeneity of the material, varying
6.3 An X-ray source that does not yield significant spectral
surface geometries, and potential critical depth effects.
interferences with the characteristic X-ray lines for the ele-
4.8 Inductively Coupled Plasma-Optical Emission Spec- ments typically found in glass is required. Several X-ray
trometry (ICP-OES) and Inductively Coupled Plasma-Mass sources are available; a rhodium X-ray source is preferred for
appropriate excitation energy and minimal spectral interfer-
Spectrometry (ICP-MS) may also be used for trace elemental
analysis of glass and offer lower minimum detection levels and ences for elements in glass. Other X-ray sources such as Mo
X-ray tubes cause interferences with discriminating elements
the ability for quantitative analysis. However, these methods
are destructive, and require larger sample sizes and much such as Zr.
longer sample preparation times (Test Method E2330).
6.4 A vacuum sample chamber, sample stage, and visual-
4.9 LaserAblation-InductivelyCoupledPlasma-MassSpec- ization system are required.
trometry (LA-ICP-MS) uses comparable specimen sizes to
6.5 The sample holder, sample support film, and mounting
those used for µ-XRF but offers better LODs, quantitative
material (for example, adhesive with low trace elements) must
capability and less analysis time. LA-ICP-MS drawbacks are
prevent background interferences.
greater instrument cost and complexity of operation.
4.10 Scanning Electron Microscopy with EDS (SEM-EDS)
is also available for elemental analysis, but it is of limited use
Available from X-ray Transition Energies Database, National Institute of
for forensic glass source discrimination due to poor detection
Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD
limits for higher atomic number elements present in glass at 20899-1070, http://physics.nist.gov/PhysRefData/XrayTrans/Html/search.html.
E2926 − 13
7. Hazards instrumental parameters used for collection of spectra from the
glass specimens. NIST SRM 1831 is a suitable sample for this
7.1 The X-ray sources emit radiation when energized. For
purpose.
operator safety, appropriate shielding and safety interlocks
must be in place and operational.
9. Procedure
9.1 Specimen Preparation:
8. Calibration and Standardization
9.1.1 Examine glass fragments using stereomicroscopy to
8.1 Apparatus—The instrument must be optimized as in
determine an appropriate preparation method for the specimen.
accordance with manufacturer’s instruction.
9.1.2 Ifnecessary,cleanthespecimentoremoveanysurface
8.1.1 Energy Calibration—calibrate the X-ray energy scale
contamination. Cleaning may include washing specimens with
to characteristic X-ray emission lines by either measuring the
soap and water, with or without ultrasonication, and rinsing in
centroid energy of a low- (<2 keV) and high- (>6 keV) energy
deionized water, followed by rinsing in acetone, methanol, or
peak or by using software provided by the instrument manu-
ethanol,anddrying.Soakinginvariousconcentrationsofnitric
facturer. For example, the aluminum (1.486 keV) and copper
acid for 30 minutes or longer, rinsing with deionized water and
(Cu) (8.040 keV) Kα-X-ray energy lines may be used.
ethanol, and drying prior to analysis removes most surface
8.1.2 Stage Calibration—For automated or multiple point
contamination without affecting the measured concentrations
analysis, initialize the stage position to assure that the stage
of elements inherent in the glass. However, the use of nitric
coordinates accurately reflect the stage position.
acid may remove any surface coating that may be present.
8.1.3 Optical Alignment:
9.1.3 Mount the specimen for analysis.
8.1.3.1 Align X-ray optics to obtain the maximum count
9.1.3.1 The specimen mounting technique depends on the
rate.
sample size and shape, beam size, X-ray fluorescence spec-
8.1.3.2 Align visualization optics to ensure that the visual
trometer chamber design and purpose of the examination.
target area coincides with the X-ray beam position.
9.1.3.2 Raise specimens off the surface of the stage for
8.1.4 Spot Size Measurement—Determine spot size of the
analysis using an X-ray transparent sample holder or support-
X-ray beam at the focal point of the visualization optics. For
ive X-ray film, or both. This positioning reduces X-ray scatter
instruments with continuous variable spot size options, deter-
off of the surface of the stage and, hence, improves sample
mine the spot size at multiple settings and interpolate the
signal-to-noise. Because analysis is performed under vacuum,
others.
ensurethatspecimensretaintheirpositiononthesampleholder
8.1.5 Reference Materials—Analyze a glass certified refer-
by securing with adhesive. Prior to analysis, analyze a small
ence material (CRM) (for example, NISTSRM 1831) to verify
amount of the adhesive to determine the presence of any
the calibration of X-ray energy lines for elements present in
elements that could interfere with those in the specimen.When
glass and determine if the instrument response is within
small amounts of adhesive are used and beam overspill (X-ray
acceptable limits. Measure this glass CRM using the same
beam extending beyond the perimeter of the specimen) is
analysis parameters as the glass specimens. Use this reference
avoided, little to no interference from the adhesive will be
glass sample to normalize element ratios for interlaboratory
observed.
comparisons, intralaboratory data collection from different
9.1.3.3 Position specimens to present as flat a surface as
analytical runs, and databasing applications to improve preci-
possible to the impinging excitation X-ray beam. If necessary,
sion.
use a small amount of adhesive to facilitate this positioning.
8.1.6 Blanks—Collect a spectrum of a specimen devoid of
9.1.3.4 For comparisons, glass specimen should be of simi-
elements having an atomic number of 11 or greater, such as the
lar size, shape, and thickness to each other. For full thickness
plastic stage plate or an area of the support material having no
fragments of float glass, comparisons should be made between
glass present. Record any system peaks present for future
similar surface types (for example, non-float surface to non-
reference.
float surface).
9.1.4 Place sample(s) in the instrument’s analysis chamber.
8.2 Quality Assurance:
For automated multiple point analyses, it may be necessary to
8.2.1 The performance of the instrument must be monitored
secure the sample/sample holder to the instrument stage.
routinely and the frequency and tolerances should be set by
9.1.5 Evacuate the chamber; samples should be run under
each laboratory.
vacuum.
8.2.1.1 Check the system calibration prior to the perfo
...
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