ASTM D6247-18

Standard Test Method for Determination of Elemental Content of Polyolefins by Wavelength Dispersive X-ray Fluorescence Spectrometry

SIGNIFICANCE AND USE
5.1 Elemental analysis serves as a quality control measure for post-reactor studies, for additive levels in formulated resins, and for finished products. X-ray fluorescence spectrometry is an accurate and relatively fast method to determine mass fractions of multiple elements in polyethylene and polypropylene materials.
SCOPE
1.1 This test method covers a general procedure for the determination of elemental content in polyolefins by wavelength-dispersive X-ray fluorescence (WDXRF) spectrometry, in mass fraction ranges typical of those contributed by additives, catalysts, and reactor processes. The elements covered by this test method include fluorine, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, chromium, and zinc in the composition ranges given in Table 1.    
1.1.1 This test method does not apply to polymers specifically formulated to contain flame retardants including brominated compounds and antimony trioxide.  
1.1.2 This test method does not apply to polymers formulated to contain high levels of compounds of vanadium, molybdenum, cadmium, tin, barium, lead, and mercury because the performance can be strongly influenced by spectral interferences or interelement effects due to these elements.
Note 1: Specific methods and capabilities of users may vary with differences in interelement effects and sensitivities, instrumentation and applications software, and practices between laboratories. Development and use of test procedures to measure particular elements, mass fraction ranges or matrices is the responsibility of individual users.
Note 2: One general method is outlined herein; alternative analytical practices can be followed, and are attached in notes, where appropriate.  
1.2 The values stated in SI units are to be regarded as the standard.  
1.3 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. Specific precautionary statements are given in Section 10.
Note 3: There is no known ISO equivalent to this standard.  
1.4 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.

General Information

• Status: Published
• Publication Date: 30-Sep-2018
• ICS: 83.020 - Manufacturing processes in the rubber and plastics industries
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.70 - Analytical Methods

Relations

• Replaces: ASTM D6247-10 - Standard Test Method for Determination of Elemental Content of Polyolefins by Wavelength Dispersive X-ray Fluorescence Spectrometry
• Effective Date: 01-Oct-2018
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM E135-20 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jan-2020
• Refers: ASTM E1601-19 - Standard Practice for Conducting an Interlaboratory Study to Evaluate the Performance of an Analytical Method
• Effective Date: 01-Nov-2019
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM E135-19 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM D6247-18 - Standard Test Method for Determination of Elemental Content of Polyolefins by Wavelength Dispersive X-ray Fluorescence Spectrometry
• Effective Date: 01-Oct-2018
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM E135-16 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2016

Overview

ASTM D6247-18: Standard Test Method for Determination of Elemental Content of Polyolefins by Wavelength Dispersive X-ray Fluorescence Spectrometry establishes a reliable and efficient procedure for analyzing the elemental composition of polyolefins, particularly polyethylene (PE) and polypropylene (PP). Utilizing wavelength dispersive X-ray fluorescence (WDXRF) spectrometry, this standard enables the accurate measurement of mass fractions of key elements found in additives, catalysts, and process residues in polyolefins. As quality and compliance requirements in plastics manufacturing become increasingly stringent, this method serves as an essential tool for both quality control and product development.

Key Topics

• Scope of Analysis: The standard method is used to determine elements such as fluorine, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, chromium, and zinc in polyolefin matrices.

• WDXRF Spectrometry: Employs primary X-rays to excite elements within a molded polyolefin specimen, causing fluorescence that is then measured by the spectrometer to quantify element presence.

• Quality Assurance: Elemental analysis supports quality control throughout post-reactor studies, additive level verification in formulated resins, and assessment of finished plastic products.

• Limitations:

  • Not applicable to polymers with flame retardant additives containing brominated compounds or antimony trioxide.
  • Not suited for polymers with high levels of vanadium, molybdenum, cadmium, tin, barium, lead, or mercury due to potential spectral interferences.

• Calibration and References: The method requires the preparation and use of calibration standards and/or certified reference materials to ensure accuracy in elemental quantification.

Applications

• Production Quality Control​: Regular monitoring of elemental content helps ensure batch-to-batch consistency, adherence to regulatory limits, and verification of additive incorporation in polyolefin resins and end products.

• Research and Development: WDXRF analysis enables rapid feedback on the impact of process conditions, new formulations, or alternative catalyst systems on polyolefin composition.

• Compliance and Certification: Manufacturers can use this method to demonstrate compliance with industry and customer specifications for elemental impurities and additive levels.

• Failure Analysis and Troubleshooting: Identifying undetected contaminants or deviations in elemental content can aid in diagnosing performance issues or product failures.

Related Standards

• ASTM D4703: Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets - Used for preparing specimens for analysis.
• ASTM E1621: Guide for Elemental Analysis by Wavelength Dispersive X-Ray Fluorescence Spectrometry - Provides additional context and guidance for elemental analysis.
• ASTM E1361: Guide for Correction of Interelement Effects in X-Ray Spectrometric Analysis - Important for handling potential matrix effects during WDXRF analysis.
• ASTM D883: Terminology Relating to Plastics - Offers definitions of relevant terms.
• JCGM 100:2008: Guide to the Expression of Uncertainty in Measurement - Reference for reporting and interpreting uncertainty.

There is no known ISO equivalent for ASTM D6247-18, making it a unique reference for elemental analysis in polyolefin materials within ASTM standards.

---

By following ASTM D6247-18, laboratories and manufacturers can obtain reproducible, precise, and reliable measurements of elemental content in polyolefins, reinforcing product quality, regulatory compliance, and the integrity of plastic materials throughout the supply chain.

Standards Content (Sample)

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.
Designation:D6247 −18
Standard Test Method for
Determination of Elemental Content of Polyolefins by
Wavelength Dispersive X-ray Fluorescence Spectrometry
This standard is issued under the fixed designation D6247; 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* 1.2 The values stated in SI units are to be regarded as the
standard.
1.1 This test method covers a general procedure for the
1.3 This standard does not purport to address all of the
determination of elemental content in polyolefins by
safety concerns, if any, associated with its use. It is the
wavelength-dispersive X-ray fluorescence (WDXRF)
responsibility of the user of this standard to establish appro-
spectrometry, in mass fraction ranges typical of those contrib-
priate safety, health, and environmental practices and deter-
uted by additives, catalysts, and reactor processes. The ele-
mine the applicability of regulatory limitations prior to use.
ments covered by this test method include fluorine, sodium,
Specific precautionary statements are given in Section 10.
magnesium, aluminum, silicon, phosphorus, sulfur, calcium,
titanium, chromium, and zinc in the composition ranges given
NOTE 3—There is no known ISO equivalent to this standard.
in Table 1.
1.4 This international standard was developed in accor-
TABLE 1 Mass Fraction Ranges for Additive and Trace Elements
dance with internationally recognized principles on standard-
in Polyolefins
ization established in the Decision on Principles for the
Element Lower Upper
Development of International Standards, Guides and Recom-
Limit Limit
(mg/kg) (mg/kg)
mendations issued by the World Trade Organization Technical
Fluorine 100 300
Barriers to Trade (TBT) Committee.
Sodium 25 200
Magnesium 10 600
Aluminum 40 500 2. Referenced Documents
Silicon 30 1000
2.1 ASTM Standards:
Phosphorus 5 200
Sulfur 20 200
C1118 Guide for Selecting Components for Wavelength-
Calcium 10 300
Dispersive X-Ray Fluorescence (XRF) Systems (With-
Titanium 5 200
drawn 2011)
Chromium 5 100
Zinc 10 1000
D883 Terminology Relating to Plastics
D4703 Practice for Compression Molding Thermoplastic
1.1.1 This test method does not apply to polymers specifi-
Materials into Test Specimens, Plaques, or Sheets
cally formulated to contain flame retardants including bromi-
D6247 Test Method for Determination of Elemental Content
nated compounds and antimony trioxide.
of Polyolefins by Wavelength Dispersive X-ray Fluores-
1.1.2 This test method does not apply to polymers formu-
cence Spectrometry
lated to contain high levels of compounds of vanadium,
E29 Practice for Using Significant Digits in Test Data to
molybdenum, cadmium, tin, barium, lead, and mercury be-
Determine Conformance with Specifications
cause the performance can be strongly influenced by spectral
E135 Terminology Relating to Analytical Chemistry for
interferences or interelement effects due to these elements.
NOTE 1—Specific methods and capabilities of users may vary with Metals, Ores, and Related Materials
differences in interelement effects and sensitivities, instrumentation and
E1361 Guide for Correction of Interelement Effects in
applications software, and practices between laboratories. Development
X-Ray Spectrometric Analysis
and use of test procedures to measure particular elements, mass fraction
E1601 Practice for Conducting an Interlaboratory Study to
ranges or matrices is the responsibility of individual users.
Evaluate the Performance of an Analytical Method
NOTE 2—One general method is outlined herein; alternative analytical
practices can be followed, and are attached in notes, where appropriate.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction ofASTM Committee D20 on Plastics contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Oct. 1, 2018. Published October 2018. Originally the ASTM website.
approved in 1998. Last previous edition approved in 2010 as D6247 - 10. DOI: The last approved version of this historical standard is referenced on
10.1520/D6247-18. www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6247−18
E1621 Guide for ElementalAnalysis by Wavelength Disper- 6. Interferences
sive X-Ray Fluorescence Spectrometry
6.1 Spectral Interferences—Spectral interferences result
2.2 Other Documents:
from the behavior of the detector subsystem of the spectrom-
JCGM 100:2008 Guide to the Expression of Uncertainty in
eter and from scattering of X-rays by the specimen. Overlaps
Measurements
among X-ray lines from elements in the specimen are caused
by the limited resolution of the detection subsystem. The
3. Terminology
degreeoflineoverlapandthebestmethodtoaccountorcorrect
3.1 Definitions:
for it must be ascertained on an individual basis and must be
3.1.1 Definitions of terms applying to XRF and plastics
considered when calibrating the instrument.
appear in Terminology E135 and Terminology D883, respec-
6.1.1 The measurement of sodium as an analyte must
tively.
include correction for the line overlap of zinc L-series lines on
3.2 Definitions of Terms Specific to This Standard:
sodium K-L .
2,3
3.2.1 infinite thickness—or critical thickness: the thickness
6.1.2 The measurement of fluorine as an analyte must
of specimen which, if increased, yields no increase in count
include correction for the overlap of magnesium K-series lines
rate of secondary (fluorescent) X-rays. This thickness varies
on background measurement angles near the fluorine K-L
2,3
with secondary X-ray energy or wavelength.
peak.
3.2.2 polyolefin—used in this context, refers to polyethylene
6.2 Interelement Effects—Interelement effects, also called
(PE) and polypropylene (PP) thermoplastics.
matrix effects, exist among all elements as the result of
absorption of fluorescent X-rays (secondary X-rays) by atoms
4. Summary of Test Method
in the specimen and the subsequent fluorescence of a fraction
4.1 The test specimen is compression molded or injection
of those atoms. Three options exist for dealing with interele-
molded into a plaque having a clean, uniform surface.
ment effects.
4.2 The plaque is irradiated in the WDXRF spectrometer
6.2.1 Mathematical Methods—A number of methods are
with a beam of primary X-rays that causes each element to
commonly utilized including full fundamental parameters (FP)
fluoresce at specific wavelengths (lines). Choices of appropri-
treatments and mathematical models based on influence coef-
atelinesandspectrometertestconditionscanvaryaccordingto
ficient algorithms. The influence coefficients are calculated
each element, and with factors such as detector response, mass
either from first principles, from the empirical data, or some
fractionrange,andotherelementspresentinthesamplematrix.
combination of the two approaches. See Guide E1361 for
4.3 The secondary X-rays are dispersed by crystals and
examples of these approaches. Also, consult the software
multilayer structures of appropriate spacing, and measured by
manual for the spectrometer for information on the approaches
appropriate detectors configured at angles specific to lines of
provided with the spectrometer.Any of these that will achieve
interest.Additional considerations appear in Guides C1118 and
the necessary analytical accuracy is acceptable. Examples of
E1621.
common interelement effects are listed in Table 2.
4.4 Analyte mass fraction is determined by relation/
6.2.2 Internal Standard or Internal Reference—This ap-
comparison of measured count rate with a calibration curve.
proach involves the correction of interelement effects by
normalizing the measured count rate of an element to the
NOTE 4—An alternative method utilizes a fundamental parameters type
measured count rate of an internal standard element or an
calibration.
internal reference line from the spectrometer.
5. Significance and Use
6.2.2.1 An internal standard element must be chosen care-
5.1 Elemental analysis serves as a quality control measure fully and must be added during sample preparation to all
specimens in a completely homogeneous manner. The chosen
forpost-reactorstudies,foradditivelevelsinformulatedresins,
and for finished products. X-ray fluorescence spectrometry is line from the internal standard element can be used for any
analyte as long as there are no absorption edges of major
an accurate and relatively fast method to determine mass
fractions of multiple elements in polyethylene and polypropyl- constituent elements between the measured line of the analyte
ene materials. and the measured line of the internal standard element.
TABLE 2 Common Interelement Effects in Formulated Plastics
Cause Effect
Polymers of similar composition but differences in the relative mass fractions of hydrogen and carbon. Differences in C/H among calibrants and samples can
result in biases of a few percent (relative).
Unmeasured elements boron, nitrogen, oxygen, and fluorine present in the matrix of the polymer, for If mass fractions differ significantly from the calibrants,
example, amide, fluorinated, and terephthalate compounds. these elements cause significant changes in both apparent
sensitivity and background count rates.
Absorption by elements in the scope of the standard or unknown levels of elements outside the scope Reduction of apparent sensitivity for most analytes.
of the standard (for example, molybdenum, cadmium, tin, and barium) included in the formulation.
D6247−18
TABLE 3 Recommended X-ray Lines for Individual Analytes
6.2.2.2 An internal reference line is a peak produced by
scattering of primary X-rays from the tube source from the Analyte Preferred Line Alternate Line
Fluorine, F K-L (Kα )
2,3 1,2
specimen into the monochromator. In most cases, it is appro-
Sodium, Na K-L (Kα )
2,3 1,2
priate to use the Compton scatter peak, if available. The
Magnesium, Mg K-L (Kα )
2,3 1,2
internal reference line can be used for any analyte as long as Aluminum, Al K-L (Kα )
2,3 1,2
Silicon, Si K-L (Kα )
2,3 1,2
there are no absorption edges of major constituent elements
Phosphorus, P K-L (Kα )
2,3 1,2
between the measured line of the analyte and the internal
Sulfur, S K-L (Kα )
2,3 1,2
Calcium, Ca K-L (Kα )
reference line.
2,3 1,2
Titanium, Ti K-L (Kα )
2,3 1,2
6.2.3 Restricted Calibration Range—In this option, the
Chromium, Cr K-L (Kα )
2,3 1,2
analyst chooses to restrict the maximum mass fractions of the
Zinc, Zn K-L (Kα)K-M (Kβ )
2,3 1,2 2,3 1,3
analytes to values below which there are no significant biases
duetoabsorption.Theanalystmustdemonstratebyexperiment
that interelement effects have been controlled completely.
7.3.2 X-ray Detectors, with sufficient sensitivity to detect
the recommended lines listed in Table 3.Typical spectrometers
NOTE 5—Differences in specimen thickness may be a source of bias
include proportional counters, sealed or flow designs, and a
when the energy of the measured X-ray line is high. Internal standard and
scintillation counter.
internal reference procedures can be used to correct for the effects of these
differences. See Section 13.
7.3.3 Signal Conditioning and Data Handling Electronics
NOTE 6—The background count rate near the peak of interest can serve
that include the functions of X-ray counting and peak process-
as an internal reference measurement in the same way as a peak from
ing.
scattered primary radiation.
7.3.4 Vacuum Pump—The X-ray optical path must be
evacuated using a mechanical pump.
7. Apparatus
7.3.5 The following spectrometer features and accessories
7.1 Calibration Standards Formulation:
are optional.
7.1.1 Batch Compounding Equipment, with temperature 7.3.5.1 Beam Filters—Used on the primary X-ray beam to
regulation capabilities, for melt homogenization of elemental make the excitation more selective and to reduce background
compounds or additives into polyolefin reference standards. count rates.
Equipment can range from small scale torque rheometers 7.3.5.2 Specimen Spinner—Use is recommended to reduce
equipped with mixing head, to large-scale batch mixers. the effect of surface irregularities of the specimen.
Nitrogen purge capabilities are recommended.
7.4 Drift Correction Monitor(s)—Due to instability of the
measurement system, the sensitivity and background of the
NOTE 7—An alternative method utilizes a single-screw or twin-screw
laboratory-scale extruder in place of the melt-fusion head, however, more spectrometer will drift with time. Drift correction monitors can
material is required for formulation. Dry homogenization techniques that
be used to correct for this drift. The optimum drift correction
do not require the use of melt-compounding apparatus have been used;
monitor specimens are permanent materials that are stable with
however, such are not recommended.
time and repeated exposure to X-rays.
7.1.2 Analytical Balance, 0.1-mg sensitivity
NOTE 10—Suitable drift correction monitors can be fused bead speci-
mens containing the relevant elements or elements that have fluorescence
7.2 Specimen Preparation:
with the same energies as the elements of interest. It is recommended that
7.2.1 Thermal Press, for compression-molding of plaques,
monitors provide count rates near to the low and high ends of the ranges
and capable of obtaining temperatures, pressures and cooling
typically encountered from plastic specimens.
rates, as recommended for PE and PPin Practice D4703 and in
7.5 Gloves—Disposable cotton gloves are recommended for
Section 11 of this test method.
handling all specimens to minimize contamination.
7.2.2 Flash Type Mold, picture-frame type, described in
7.6 Personal Protective Equipment—Appropriate personal
Practice D4703: stainless-steel chase to mold test plaques,
protective equipment for the handling of reagents and hot
uncoated polyester film parting sheets, and smooth, stainless
equipment.
steel backing plates of minimum 2.5 mm thickness.
NOTE 8—Injection molding apparatus have also been employed, in 8. Reagents and Materials
place of the thermal press and flash mold.
8.1 P-10 Gas, a mixture of 90 % argon and 10 % methane,
NOTE 9—One laboratory has prepared plaques using standard steel dies
ultra-high purity or equivalent, for use with gas-flow propor-
(designed for preparing briquettes of powder materials) in a hydraulic
tional detectors.
press. Aluminum pressing caps served as molds. The loaded die was
heated in an oven for≥2 h prior to pressing. During pressing, a laboratory
NOTE 11—Some instrument manufacturers allow the use of P-5 gas
vacuum was drawn on the side port of the die. In the press, the pressure
(95 % argon and 5 % methane).
was rapidly increased to 12 tons and the die was allowed to cool to room
temperature. The pressing cap was removed from the cooled plaque.
8.2 Nitrogen, prepurified grade or equivalent, for purging
the melt fusion chamber.
7.3 Spectrometer—Requirements for a wavelength-
dispersiveXRFspectrometerareoutlinedinGuides C1118and
8.3 Elemental Standards—Compoundsoradditives,orboth,
E1621.
to be melt-homogenized into polymer calibration standards.
7.3.1 Source of X-ray Excitation, capable of exciting the Materials must have reliable elemental assays or known
recommended lines listed in Table 3, typically an X-ray tube. stoichiometry prior to use.
D6247−18
NOTE 12—One laboratory has prepared polymer calibration standards
D4703. If the resulting plaque is too large in diameter to fit the
by dissolving organometallic compounds in xylenes and adding known
instrument, cut or punch a piece of the correct diameter.
amounts to low density polyethylene dissolved in xylenes in TFE-
flurocarbon beakers at 100°C with stirring.After removal of the solvents,
NOTE 16—Use of a laboratory-scale injection molding technique is an
the solids were ground in an ultracentrifugal mill and melt pressed.
acceptable alternative to the compression molding method.
NOTE 17—Laboratories and manufacturers of reference materials em-
9. Reference Materials
ploy plaques having different thickness. Thinner specimens will be less
than infinitely thick for zinc X-rays, and if <2 mm thick, they are less than
9.1 Users can prepare reference materials in house. A
infinitely thick for chromium X-rays. It is recommended to employ a
technique that offers consistent elemental dispersion through-
narrow range of thickness for optimum method performance.
out the calibration standard must be followed. Melt homogeni-
11.2.1 Weigh the required mass of plastic and place into the
zation to ensure uniformity is recommended; see Annex A1.
compression or molding apparatus.
NOTE 13—Resins from actual production runs have been used for
11.2.2 Place the assembly into the press or oven, which has
calibration standards, after value assignment by independent analytical
methods. been preheated. Compress the sample under appropriate pres-
NOTE 14—One laboratory has successfully used glass reference mate-
sure and time settings to obtain a suitable specimen plaque.
rials and fundamental parameters-based calibrations. Another laboratory
has successfully used oil-based reference materials to calibrate a method.
NOTE 18—Appropriate temperatures vary depending on the apparatus.
For example, thermal presses and flash molds are set to 175°C for PE and
9.2 Certified reference materials are available from national
200°C for PP. For steel briquette dies, temperatures of 140°C for PE and
metrology institutes and commercial suppliers.
185°C for PP have been used successfully.
10. Safety Precautions 11.3 Cooling Rate is chosen to yield a uniform, smooth
plaque.
10.1 Occupational Health and Safety Standards for X-rays,
11.3.1 Programmed Cooling—After a pre-programmed
and ionizing radiation shall be observed. It is also recom-
dwell time at high pressure, initiate cooling at a recommended
mended that proper practices be followed, as shown in Guide
rate of 15 6 2°C per minute,
E1621.
11.3.2 Quick Cooling—Remove the hot assembly and pres-
NOTE 15—X-rays are dangerous and can cause serious personal injury.
surize in a water-cooled press, or equivalent, and allow it to
X-ray beams can be very narrow and difficult to detect. Precautions taken
cool to ambient temperature, or
minimize potential radiation exposure include an increase in protective
shielding, an increase of distance, and a decrease of time near any
11.3.3 Slow Cooling—When using a steel briquette die,
suspected source of leakage. Modern commercial spectrometers typically
allowthedietocoolundisturbedinthehydraulicpresstoroom
have the appropriate shielding and safety interlocks. It is possible that
temperature.
local safety codes or regulations demand monitoring equipment; and/or
regular safety checks. Refer to 1.3.
11.4 It is recommended to clean specimen surfaces with
10.2 Chemical—Appropriate precautions for chemical haz-
isopropyl alcohol or ethyl alcohol, immediately prior to mea-
ards shall be observed for any chemicals and materials used in
surement. The need for this cleaning varies with the elements
preparingcalibrationstandards.Consultthesuppliers’Material
and/or the additives to be measured, as well as the specimen
Safety Data Sheets for specific hazards and safety practices.
preparation and specimen handling. Experience gained during
the routine application of this standard test method provides
10.3 Pressurized Gas—Requires safe and proper handling
good guidance in this respect.
practices.
11.4.1 Care shall be taken to handle only the sides, not the
10.4 Specimen Preparation—Follow appropriate precau-
surfaces of the specimen following molding or cleaning so that
tions when using hot equipment for homogenization and
oils and salts from the skin do not contaminate the specimen.
specimen preparation. Consult the manufacturer’s recommen-
The use of disposable cotton gloves when handling specimens
dations for specific practices.
reduces the risk of inadvertent contamination.
11. Preparation of Reference Materials and Test
12. Preparation of Apparatus
Specimens
11.1 Specimen Plaques—Consistent preparation of refer-
12.1 A description of considerations is included in Guide
ence materials and test specimens is essential. Variations in
E1621.
sample thickness, surface finish and homogeneity can affect
12.2 Allow the WDXRF spectrometer to stabilize for op-
reliability of results.
eration according to the manufacturer’s guidelines or the
11.1.1 Test Specimens—A potential source of bias is intro-
laboratory operating procedure.
duced when one or more elements are not distributed homo-
geneously throughout the specimen. This cannot be corrected
12.3 In a manner consistent with the manufacturer’s
for. See Annex A1 for procedures designed to reduce hetero-
recommendations, set up measurement conditions (X-ray tube
geneity.
excitation voltage, tube current, filters, goniometer angles,
pulse height discrimination, etc.) to measure the count rates of
11.2 Compression Molding—Both calibration standards and
the preferred lines (or alternate lines) of the analytes.
test specimens are pressed into plaques. The laboratory must
choose a thickness and use it consistently. Each plaque shall 12.3.1 Include subtraction of background for all elements.
have a smooth, plane surface, and no voids. Refer to Practice Measure at least one background point for each element.
D6247−18
12.4 If applicable, include measurement of the Compton 13.3.1 In an empirical approach with a low number of
scatter radiation resulting from scatter of X-ray tube charac- calibration standards, calculate influence coefficients from
teristic lines from the samples. theory (using FP).
12.4.1 The use of the background count rate for the element
13.3.2 Place each standard specimen in the X-ray beam and
is an alternative to the Compton scatter radiation.
measure the net count rate of each element using the measure-
ment conditions chosen in Section 12.
NOTE 19—Depending on the anode material of the X-ray tube,
13.3.3 Measure each standard at least twice preferably with
Compton scatter radiation may or may not be observable. For example,
tubes with anodes of Mo, Rh, Ag, Pd (atomic numbers 42 and higher) two independently prepared specimens.
provide strong Compton scatter radiation. In contrast, tube anodes
13.3.4 For each analyte, follow the manufacturer’s instruc-
consisting of chromium and scandium are of little or no use as an internal
tions to perform a regression of net count rate versus mass
reference, as they exhibit very little Compton scatter.
fraction.
12.5 For each analyte, calculate a minimum counting time
NOTE22—Linearcalibrationcurveswerefoundbysomelaboratoriesto
resulting in a maximum counting statistical error (%CSE) of
be suitable for the element mass fractions listed in the scope of this test
less than 2 % for a specimen containing approximately 100
method.
mg/kg of the analyte. The required counting time may be
NOTE 23—X-ray fluorescence data for calibration is heteroscedastic.
calculated by using Eq 1:
This means that calibration regressions that include a weighting scheme
that favors low mass fraction calibration st
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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: D6247 − 10 D6247 − 18
Standard Test Method for
Determination of Elemental Content of Polyolefins by
Wavelength Dispersive X-ray Fluorescence Spectrometry
This standard is issued under the fixed designation D6247; 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 Scope*
1.1 This test method covers a general procedure for the determination of elemental content in polyolefins by wavelength-
dispersive X-ray fluorescence (WDXRF) spectrometry, in mass fraction ranges typical of those contributed by additives, catalysts,
and reactor processes. The elements covered by this test method include fluorine, sodium, magnesium, aluminum, silicon,
phosphorus, sulfur, calcium, titanium, chromium, and zinc in the composition ranges given in Table 1.
TABLE 1 Mass Fraction Ranges for Additive and Trace Elements in Polyolefins
Element Lower Upper
Limit Limit
(mg/kg) (mg/kg)
Fluorine 100 300
Sodium 25 200
Magnesium 10 600
Aluminum 40 500
Silicon 30 1000
Phosphorus 5 200
Sulfur 20 200
Calcium 10 300
Titanium 5 200
Chromium 5 100
Zinc 10 1000
1.1.1 This test method does not apply to polymers specifically formulated to contain flame retardants including brominated
compounds and antimony trioxide.
1.1.2 This test method does not apply to polymers formulated to contain high levels of compounds of vanadium, molybdenum,
cadmium, tin, barium, lead, and mercury because the performance maycan be strongly influenced by spectral interferences or
interelement effects due to these elements.
NOTE 1—Specific methods and capabilities of users may vary with differences in interelement effects and sensitivities, instrumentation and applications
software, and practices between laboratories. Development and use of test procedures to measure particular elements, mass fraction ranges or matrices
is the responsibility of individual users.
NOTE 2—One general method is outlined herein; alternative analytical practices can be followed, and are attached in notes, where appropriate.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 10.
NOTE 3—There is no known ISO equivalent to this standard.
1.4 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.
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
Current edition approved Aug. 1, 2010Oct. 1, 2018. Published September 2010October 2018. Originally approved in 1998. Last previous edition approved in 20042010
as D6247 - 98D6247 - 10.(2004). DOI: 10.1520/D6247-10.10.1520/D6247-18.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6247 − 18
2. Referenced Documents
2.1 ASTM Standards:
C1118 Guide for Selecting Components for Wavelength-Dispersive X-Ray Fluorescence (XRF) Systems (Withdrawn 2011)
D883 Terminology Relating to Plastics
D4703 Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets
D6247 Test Method for Determination of Elemental Content of Polyolefins by Wavelength Dispersive X-ray Fluorescence
Spectrometry
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E1361 Guide for Correction of Interelement Effects in X-Ray Spectrometric Analysis
E1601 Practice for Conducting an Interlaboratory Study to Evaluate the Performance of an Analytical Method
E1621 Guide for Elemental Analysis by Wavelength Dispersive X-Ray Fluorescence Spectrometry
2.2 Other Documents:
JCGM 100:2008 Guide to the Expression of Uncertainty in Measurements
3. Terminology
3.1 Definitions:
3.1.1 Definitions of terms applying to XRF and plastics appear in Terminology E135 and Terminology D883, respectively.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 element—used in this context, refers to any chemical element that can be determined by XRF; and is often used
synonymously with the term metal.
3.2.1 infinite thickness—or critical thickness: the thickness of specimen which, if increased, yields no increase in count rate of
secondary (fluorescent) X-rays. This thickness varies with secondary X-ray energy or wavelength.
3.2.2 polyolefin—used in this context, refers to polyethylene (PE) and polypropylene (PP) thermoplastics.
4. Summary of Test Method
4.1 The test specimen is compression molded or injection molded into a plaque having a clean, uniform surface.
4.2 The plaque is irradiated in the WDXRF spectrometer with a beam of primary X-rays that causes each element to fluoresce
at specific wavelengths (lines). Choices of appropriate lines and spectrometer test conditions can vary according to each element,
and with factors such as detector response, mass fraction range, and other elements present in the sample matrix.
4.3 The secondary X-rays are dispersed by crystals and multilayer structures of appropriate spacing, and measured by
appropriate detectors configured at angles specific to lines of interest. Additional considerations appear in Guides C1118 and
E1621.
4.4 Analyte mass fraction is determined by relation/comparison of measured count rate with a calibration curve.
NOTE 4—An alternative method utilizes a fundamental parameters type calibration.
5. Significance and Use
5.1 Elemental analysis serves as a quality control measure for post-reactor studies, for additive levels in formulated resins, and
for finished products. X-ray fluorescence spectrometry is an accurate and relatively fast method to determine mass fractions of
multiple elements in polyethylene and polypropylene materials.
6. Interferences
6.1 Spectral Interferences—Spectral interferences result from the behavior of the detector subsystem of the spectrometer and
from scattering of X rays X-rays by the specimen. Overlaps among X-ray lines from elements in the specimen are caused by the
limited resolution of the detection subsystem. The degree of line overlap and the best method to account or correct for it must be
ascertained on an individual basis and must be considered when calibrating the instrument.
6.1.1 The measurement of sodium as an analyte must include correction for the line overlap of zinc L-series lines on sodium
K-L .
2,3
6.1.2 The measurement of fluorine as an analyte must include correction for the overlap of magnesium K-series lines on
background measurement angles near the fluorine K-L peak.
2,3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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.
D6247 − 18
6.2 Interelement Effects—Interelement effects, also called matrix effects, exist among all elements as the result of absorption of
fluorescent X rays (secondary X rays) X-rays (secondary X-rays) by atoms in the specimen and the subsequent fluorescence of a
fraction of those atoms. Three options exist for dealing with interelement effects.
6.2.1 Mathematical Methods—A number of methods are commonly utilized including full fundamental parameters (FP)
treatments and mathematical models based on influence coefficient algorithms. The influence coefficients are calculated either from
first principles, from the empirical data, or some combination of the two approaches. See Guide E1361 for examples of these
approaches. Also, consult the software manual for the spectrometer for information on the approaches provided with the
spectrometer. Any of these that will achieve the necessary analytical accuracy is acceptable. Examples of common interelement
effects are listed in Table 2.
6.2.2 Internal Standard or Internal Reference—This approach involves the correction of interelement effects by normalizing the
measured count rate of an element to the measured count rate of an internal standard element or an internal reference line from
the spectrometer.
6.2.2.1 An internal standard element must be chosen carefully and must be added during sample preparation to all specimens
in a completely homogeneous manner. The chosen line from the internal standard element can be used for any analyte as long as
there are no absorption edges of major constituent elements between the measured line of the analyte and the measured line of the
internal standard element.
6.2.2.2 An internal reference line is a peak produced by scattering of primary X rays X-rays from the tube source from the
specimen into the monochromator. In most cases, it is appropriate to use the Compton scatter peak, if available. The internal
reference line can be used for any analyte as long as there are no absorption edges of major constituent elements between the
measured line of the analyte and the internal reference line.
6.2.3 Restricted Calibration Range—In this option, the analyst chooses to restrict the maximum mass fractions of the analytes
to values below which there are no significant biases due to absorption. The analyst must demonstrate by experiment that
interelement effects have been controlled completely.
NOTE 5—Differences in specimen thickness may be a source of bias when the energy of the measured X-ray line is high. Internal standard and internal
reference procedures can be used to correct for the effects of these differences. See Section 13.
NOTE 6—The background count rate near the peak of interest can serve as an internal reference measurement in the same way as a peak from scattered
primary radiation.
7. Apparatus
7.1 Calibration Standards Formulation:
7.1.1 Batch Compounding Equipment, with temperature regulation capabilities, for melt homogenization of elemental
compounds or additives into polyolefin reference standards. Equipment can range from small scale torque rheometers equipped
with mixing head, to large-scale batch mixers. Nitrogen purge capabilities are recommended.
NOTE 7—An alternative method utilizes a single-screw or twin-screw laboratory-scale extruder in place of the melt-fusion head, however, more material
is required for formulation. Dry homogenization techniques that do not require the use of melt-compounding apparatus have been used; however, such
are not recommended.
7.1.2 Analytical Balance, 0.1-mg sensitivity
7.2 Specimen Preparation:
7.2.1 Thermal Press, for compression-molding of plaques, and capable of obtaining temperatures, pressures and cooling rates,
as recommended for PE and PP in Practice D4703 and in Section 11 of this test method.
7.2.2 Flash Type Mold, picture-frame type, described in Practice D4703: stainless-steel chase to mold test plaques, uncoated
polyester film parting sheets, and smooth, stainless steel backing plates of minimum 2.5 mm thickness.
NOTE 8—Injection molding apparatus have also been employed, in place of the thermal press and flash mold.
NOTE 9—One laboratory has prepared plaques using standard,standard steel dies (designed for preparing briquettes of powder materials) in a hydraulic
press. Aluminum pressing caps served as molds. The loaded die was heated in an oven for ≥2 h prior to pressing. During pressing, a laboratory vacuum
was drawn on the side port of the die. In the press, the pressure was rapidly increased to 12 tons and the die was allowed to cool to room temperature.
The pressing cap was removed from the cooled plaque.
TABLE 2 Common Interelement Effects in Formulated Plastics
Cause Effect
Polymers of similar composition but differences in the relative mass fractions of hydrogen and carbon. Differences in C/H among calibrants and samples can
result in biases of a few percent (relative).
Unmeasured elements boron, nitrogen, oxygen, and fluorine present in the matrix of the polymer, for If mass fractions differ significantly from the calibrants,
example, amide, fluorinated, and terephthalate compounds. these elements cause significant changes in both apparent
sensitivity and background count rates.
Absorption by elements in the scope of the standard or unknown levels of elements outside the scope Reduction of apparent sensitivity for most analytes.
of the standard (for example, molybdenum, cadmium, tin, and barium) included in the formulation.
D6247 − 18
7.3 Spectrometer—Requirements for a wavelength-dispersive XRF spectrometer are outlined in Guides C1118 and E1621.
7.3.1 Source of X-ray Excitation, capable of exciting the recommended lines listed in Table 3, typically an X-ray tube.
7.3.2 X-ray Detectors, with sufficient sensitivity to detect the recommended lines listed in Table 3. Typical spectrometers
include proportional counters, sealed or flow designs, and a scintillation counter.
7.3.3 Signal conditioning and data handling electronicsConditioning and Data Handling Electronics that include the functions
of X-ray counting and peak processing.
7.3.4 Vacuum Pump—The X-ray optical path must be evacuated using a mechanical pump.
7.3.5 The following spectrometer features and accessories are optional.
7.3.5.1 Beam Filters—Used on the primary X-ray beam to make the excitation more selective and to reduce background count
rates.
7.3.5.2 Specimen Spinner—Use is recommended to reduce the effect of surface irregularities of the specimen.
7.4 Drift Correction Monitor(s)—Due to instability of the measurement system, the sensitivity and background of the
spectrometer maywill drift with time. Drift correction monitors maycan be used to correct for this drift. The optimum drift
correction monitor specimens are permanent materials that are stable with time and repeated exposure to X rays.X-rays.
NOTE 10—Suitable drift correction monitors can be fused bead specimens containing the relevant elements or elements that have fluorescence with the
same energies as the elements of interest. It is recommended that monitors provide count rates near to the low and high ends of the ranges typically
encountered from plastic specimens.
7.5 Gloves—Disposable cotton gloves are recommended for handling all specimens to minimize contamination.
7.6 Personal Protective Equipment—Appropriate personal protective equipment for the handling of reagents and hot equipment.
8. Reagents and Materials
8.1 P-10 Gas, a mixture of 90 % argon and 10 % methane, ultra-high purity or equivalent, for use with gas-flow proportional
detectors.
NOTE 11—Some instrument manufacturers allow the use of P-5 gas (95 % argon and 5 % methane).
8.2 Nitrogen, prepurified grade or equivalent, for purging the melt fusion chamber.
8.3 Elemental Standards—Compounds or additives, or both, to be melt homogenized melt-homogenized into polymer
calibration standards. Materials must have reliable elemental assays or known stoichiometry prior to use.
NOTE 12—One laboratory has prepared polymer calibration standards by dissolving organometallic compounds in xylenes and adding known amounts
to low density polyethylene dissolved in xylenes in TFE-flurocarbon beakers at 100°C with stirring. After removal of the solvents, the solids were ground
in an ultracentrifugal mill and melt pressed.
9. Reference Materials
9.1 Users can prepare reference materials in house. A technique that offers consistent elemental dispersion throughout the
calibration standard must be followed. Melt homogenization to ensure uniformity is recommended; see Annex A1.
NOTE 13—Resins from actual production runs have been used for calibration standards, after value assignment by independent analytical methods.
NOTE 14—One laboratory has successfully used glass reference materials and fundamental parameters-based calibrations. Another laboratory has
successfully used oil-based reference materials to calibrate a method.
9.2 Certified reference materials are available from national metrology institutes and commercial suppliers.
10. Safety Precautions
10.1 Occupational Health and Safety Standards for X-rays, and ionizing radiation shall be observed. It is also recommended
that proper practices be followed, as shown in Guide E1621.
TABLE 3 Recommended X-ray Lines for Individual Analytes
Analyte Preferred Line Alternate Line
Fluorine K-L (Kα )
2,3 1,2
Fluorine, F K-L (Kα )
2,3 1,2
Sodium, Na K-L (Kα )
2,3 1,2
Magnesium K-L (Kα )
2,3 1,2
Magnesium, Mg K-L (Kα )
2,3 1,2
Aluminum K-L (Kα )
2,3 1,2
Aluminum, Al K-L (Kα )
2,3 1,2
Silicon, Si K-L (Kα )
2,3 1,2
Phosphorus, P K-L (Kα )
2,3 1,2
Sulfur, S K-L (Kα )
2,3 1,2
Calcium, Ca K-L (Kα )
2,3 1,2
Titanium, Ti K-L (Kα )
2,3 1,2
Chromium, Cr K-L (Kα )
2,3 1,2
Zinc, Zn K-L (Kα ) K-M (Kβ )
2,3 1,2 2,3 1,3
D6247 − 18
NOTE 15—X rays X-rays are dangerous and can cause serious personal injury. X-ray beams can be very narrow and difficult to detect. Precautions taken
minimize potential radiation exposure include an increase in protective shielding, an increase of distance, and a decrease of time near any suspected source
of leakage. Modern commercial spectrometers typically have the appropriate shielding and safety interlocks. Monitoring equipment may be required by
local safety codes.It is possible that local safety codes or regulations demand monitoring equipment; and/or regular safety checks. Refer to 1.3.
10.2 Chemical—Appropriate precautions for chemical hazards shall be observed for any chemicals and materials used in
preparing calibration standards. Consult the suppliers’ Material Safety Data Sheets for specific hazards and safety practices.
10.3 Pressurized Gas Gas—requiresRequires safe and proper handling practices.
10.4 Specimen Preparation—Follow appropriate precautions when using hot equipment for homogenization and specimen
preparation. Consult the manufacturer’s recommendations for specific practices.
11. Preparation of Reference Materials and Test Specimens
11.1 Specimen Plaques—Consistent preparation of reference materials and test specimens is essential. Variations in sample
thickness, surface finish and homogeneity can affect reliability of results.
11.1.1 Test Specimens—The level of heterogeneity of an element in a specimen may not be known. For most of the elements
in this standard, heterogeneity is a potential source of bias. A potential source of bias is introduced when one or more elements
are not distributed homogeneously throughout the specimen. This cannot be corrected for. See Annex A1 for procedures designed
to reduce heterogeneity.
11.2 Compression Molding—Both calibration standards and test specimens are pressed into plaques. The laboratory must choose
a thickness and use it consistently. Each plaque shall have a smooth, plane surface, and no voids. Refer to Practice D4703. If the
resulting plaque is too large in diameter to fit the instrument, cut or punch a piece of the correct diameter.
NOTE 16—Use of a laboratory-scale injection molding technique is an acceptable alternative to the compression molding method.
NOTE 17—Laboratories and manufacturers of reference materials employ plaques having different thickness. Thinner specimens will be less than
infinitely thick for zinc X rays, X-rays, and if <2 mm thick, may bethey are less than infinitely thick for chromium X rays. X-rays. It is recommended
to employ a narrow range of thickness for optimum method performance.
11.2.1 Weigh the required mass of plastic and place into the compression or molding apparatus.
11.2.2 Place the assembly into the press or oven, which has been preheated. Compress the sample under appropriate pressure
and time settings to obtain a suitable specimen plaque.
NOTE 18—Appropriate temperatures vary depending on the apparatus. For example, thermal presses and flash molds are set to 175°C for PE and 200°C
for PP. For steel briquette dies, temperatures of 140°C for PE and 185°C for PP have been used successfully.
11.3 Cooling Rate is chosen to yield a uniform, smooth plaque.
11.3.1 Programmed Cooling—After a pre-programmed dwell time at high pressure, initiate cooling at a recommended rate of
15 6 2°C per minute,
11.3.2 Quick Cooling—Remove the hot assembly and pressurize in a water-cooled press, or equivalent, and allow it to cool to
ambient temperature, or
11.3.3 Slow Cooling—When using a steel briquette die, allow the die to cool undisturbed in the hydraulic press to room
temperature.
11.4 It is recommended to clean specimen surfaces with isopropyl alcohol (or methyl alcohol),or ethyl alcohol, immediately
prior to measurement. Operator experience may show this need to vary with the element or additive to be measured.The need for
this cleaning varies with the elements and/or the additives to be measured, as well as the specimen preparation and specimen
handling. Experience gained during the routine application of this standard test method provides good guidance in this respect.
11.4.1 Care shall be taken to handle only the sides, not the surfaces of the specimen following molding or cleaning so that oils
and salts from the skin do not contaminate the specimen. Disposable cotton gloves may be wornThe use of disposable cotton gloves
when handling specimens to prevent reduces the risk of inadvertent contamination.
12. Preparation of Apparatus
12.1 A description of considerations is included in Guide E1621.
12.2 Allow the WDXRF spectrometer to stabilize for operation according to the manufacturer’s guidelines or the laboratory
operating procedure.
12.3 In a manner consistent with the manufacturer’s recommendations, set up measurement conditions (X-ray tube excitation
voltage, tube current, filters, goniometer angles, pulse height discrimination, etc.) to measure the count rates of the preferred lines
(or alternate lines) of the analytes.
12.3.1 Include subtraction of background for all elements. Measure at least one background point for each element.
12.4 If applicable, include measurement of the Compton scatter radiation resulting from scatter of X-ray tube characteristic lines
from the samples.
12.4.1 The use of the background count rate for the element is an alternative to the Compton scatter radiation.
D6247 − 18
NOTE 19—Depending on the anode material of the X-ray tube, Compton scatter radiation may or may not be observable. For example, tubes with
anodes of Mo, Rh, Ag, Pd (atomic numbers 42 and higher) provide strong Compton scatter radiation. In contrast, tube anodes consisting of chromium
and scandium are of little or no use as an internal reference. reference, as they exhibit very little Compton scatter.
12.5 For each analyte, calculate a minimum counting time resulting in a maximum counting statistical error (%CSE) of less than
2 % for a specimen containing approximately 100 mg/kg of the analyte. The required counting time may be calculated by using
Eq 1:
%CSE 5 100/= R·t (1)
~ !
where:
R 5 net count rate in counts per second and
~ !
t 5 counting time in seconds.
This corresponds to the time necessary to collect more than 2500 counts. Overall measurement time for all analytes shall not
exceed 20 min per specimen.
NOTE 20—Often, the operating system of the spectrometer will include procedures for calculating measurement times. Such procedures typically
include background measurement times, if appropriate.
NOTE 21—Polymer materials are subject to damage by ionizing radiation. Susceptibility to damage varies greatly among common polymers. The user
is cautioned to keep measurement times as short as practical and to avoid the repeat
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