1、Designation: D6247 10Standard Test Method forDetermination of Elemental Content of Polyolefins byWavelength Dispersive X-ray Fluorescence Spectrometry1This standard is issued under the fixed designation D6247; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a general procedure for thedetermination of elemental c
3、ontent in polyolefins bywavelength-dispersive X-ray fluorescence (WDXRF) spec-trometry, in mass fraction ranges typical of those contributedby additives, catalysts, and reactor processes. The elementscovered by this test method include fluorine, sodium, magne-sium, aluminum, silicon, phosphorus, sul
4、fur, calcium, titanium,chromium, and zinc in the composition ranges given in Table1.TABLE 1 Mass Fraction Ranges for Additive and Trace Elementsin PolyolefinsElement LowerLimit(mg/kg)UpperLimit(mg/kg)Fluorine 100 300Sodium 25 200Magnesium 10 600Aluminum 40 500Silicon 30 1000Phosphorus 5 200Sulfur 20
5、 200Calcium 10 300Titanium 5 200Chromium 5 100Zinc 10 10001.1.1 This test method does not apply to polymers specifi-cally formulated to contain flame retardants including bromi-nated compounds and antimony trioxide.1.1.2 This test method does not apply to polymers formu-lated to contain high levels
6、of compounds of vanadium,molybdenum, cadmium, tin, barium, lead, and mercury be-cause the performance may be strongly influenced by spectralinterferences or interelement effects due to these elements.NOTE 1Specific methods and capabilities of users may vary withdifferences in interelement effects an
7、d sensitivities, instrumentation andapplications software, and practices between laboratories. Developmentand use of test procedures to measure particular elements, mass fractionranges or matrices is the responsibility of individual users.NOTE 2One general method is outlined herein; alternative anal
8、yticalpractices can be followed, and are attached in notes, where appropriate.1.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this stan
9、dard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in Section 10.NOTE 3There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2C1118 Guid
10、e for Selecting Components for Wavelength-Dispersive X-Ray Fluorescence (XRF) SystemsD883 Terminology Relating to PlasticsD4703 Practice for Compression Molding ThermoplasticMaterials into Test Specimens, Plaques, or SheetsD6247 Test Method for Analysis of Elemental Content inPolyolefins By X-ray Fl
11、uorescence SpectrometryE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE1361 Guide for Correction of Interelement Effects inX-Ray Spectrometric AnalysisE1601 Prac
12、tice for Conducting an Interlaboratory Study toEvaluate the Performance of an Analytical MethodE1621 Guide for X-Ray Emission Spectrometric Analysis3. Terminology3.1 Definitions:3.1.1 Definitions of terms applying to XRF and plasticsappear in Terminology E135 and Terminology D883, respec-tively.1Thi
13、s test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved Aug. 1, 2010. Published September 2010. Originallyapproved in 1998. Last previous edition approved in 2004 as D6247 - 98(200
14、4).DOI: 10.1520/D6247-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 B
15、arr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2 Definitions of Terms Specific to This Standard:3.2.1 elementused in this context, refers to any chemicalelement that can be determined by XRF; and is often usedsynonymously with the term metal.3.2.2 infinite thickness
16、or critical thickness: the thicknessof specimen which, if increased, yields no increase in countrate of secondary (fluorescent) X-rays. This thickness varieswith secondary X-ray energy or wavelength.3.2.3 polyolefinused in this context, refers to polyethylene(PE) and polypropylene (PP) thermoplastic
17、s.4. Summary of Test Method4.1 The test specimen is compression molded or injectionmolded into a plaque having a clean, uniform surface.4.2 The plaque is irradiated in the WDXRF spectrometerwith a beam of primary X-rays that causes each element tofluoresce at specific wavelengths (lines). Choices of
18、 appropri-ate lines and spectrometer test conditions can vary according toeach element, and with factors such as detector response, massfraction range, and other elements present in the sample matrix.4.3 The secondary X-rays are dispersed by crystals andmultilayer structures of appropriate spacing,
19、and measured byappropriate detectors configured at angles specific to lines ofinterest.Additional considerations appear in Guides C1118 andE1621.4.4 Analyte mass fraction is determined by relation/comparison of measured count rate with a calibration curve.NOTE 4An alternative method utilizes a funda
20、mental parameters typecalibration.5. Significance and Use5.1 Elemental analysis serves as a quality control measurefor post-reactor studies, for additive levels in formulated resins,and for finished products. X-ray fluorescence spectrometry isan accurate and relatively fast method to determine massf
21、ractions of multiple elements in polyethylene and polypropy-lene materials.6. Interferences6.1 Spectral InterferencesSpectral interferences resultfrom the behavior of the detector subsystem of the spectrom-eter and from scattering of X rays by the specimen. Overlapsamong X-ray lines from elements in
22、 the specimen are causedby the limited resolution of the detection subsystem. Thedegree of line overlap and the best method to account or correctfor it must be ascertained on an individual basis and must beconsidered when calibrating the instrument.6.1.1 The measurement of sodium as an analyte musti
23、nclude correction for the line overlap of zinc L-series lines onsodium K-L2,3.6.1.2 The measurement of fluorine as an analyte mustinclude correction for the overlap of magnesium K-series lineson background measurement angles near the fluorine K-L2,3peak.6.2 Interelement EffectsInterelement effects,
24、also calledmatrix effects, exist among all elements as the result ofabsorption of fluorescent X rays (secondary X rays) by atomsin the specimen and the subsequent fluorescence of a fractionof those atoms. Three options exist for dealing with interele-ment effects.6.2.1 Mathematical MethodsA number o
25、f methods arecommonly utilized including full fundamental parameters (FP)treatments and mathematical models based on influence coef-ficient algorithms. The influence coefficients are calculatedeither from first principles, from the empirical data, or somecombination of the two approaches. See Guide
26、E1361 forexamples of these approaches. Also, consult the softwaremanual for the spectrometer for information on the approachesprovided with the spectrometer. Any of these that will achievethe necessary analytical accuracy is acceptable. Examples ofcommon interelement effects are listed in Table 2.6.
27、2.2 Internal Standard or Internal ReferenceThis ap-proach involves the correction of interelement effects bynormalizing the measured count rate of an element to themeasured count rate of an internal standard element or aninternal reference line from the spectrometer.6.2.2.1 An internal standard elem
28、ent must be chosen care-fully and must be added during sample preparation to allspecimens in a completely homogeneous manner. The chosenline from the internal standard element can be used for anyanalyte as long as there are no absorption edges of majorconstituent elements between the measured line o
29、f the analyteand the measured line of the internal standard element.6.2.2.2 An internal reference line is a peak produced byscattering of primary X rays from the tube source from thespecimen into the monochromator. In most cases, it is appro-priate to use the Compton scatter peak, if available. Thei
30、nternal reference line can be used for any analyte as long asthere are no absorption edges of major constituent elementsbetween the measured line of the analyte and the internalreference line.6.2.3 Restricted Calibration RangeIn this option, theanalyst chooses to restrict the maximum mass fractions
31、of theanalytes to values below which there are no significant biasesTABLE 2 Common Interelement Effects in Formulated PlasticsCause EffectPolymers of similar composition but differences in the relative massfractions of hydrogen and carbon.Differences in C/H among calibrants and samples can result in
32、biases of a few percent (relative).Unmeasured elements boron, nitrogen, oxygen, and fluorine presentin the matrix of the polymer, for example, amide, fluorinated, andterephthalate compounds.If mass fractions differ significantly from the calibrants, theseelements cause significant changes in both ap
33、parent sensitivity andbackground count rates.Absorption by elements in the scope of the standard or unknownlevels of elements outside the scope of the standard (for example,molybdenum, cadmium, tin, and barium) included in the formulation.Reduction of apparent sensitivity for most analytes.D6247 102
34、due to absorption. The analyst must demonstrate by experimentthat interelement effects have been controlled completely.NOTE 5Differences in specimen thickness may be a source of biaswhen the energy of the measured X-ray line is high. Internal standard andinternal reference procedures can be used to
35、correct for the effects of thesedifferences. See Section 13.NOTE 6The background count rate near the peak of interest can serveas an internal reference measurement in the same way as a peak fromscattered primary radiation.7. Apparatus7.1 Calibration Standards Formulation:7.1.1 Batch Compounding Equi
36、pment, with temperatureregulation capabilities, for melt homogenization of elementalcompounds or additives into polyolefin reference standards.Equipment can range from small scale torque rheometersequipped with mixing head, to large-scale batch mixers.Nitrogen purge capabilities are recommended.NOTE
37、 7An alternative method utilizes a single-screw or twin-screwlaboratory-scale extruder in place of the melt-fusion head, however, morematerial is required for formulation. Dry homogenization techniques thatdo not require the use of melt-compounding apparatus have been used;however, such are not reco
38、mmended.7.1.2 Analytical Balance, 0.1-mg sensitivity7.2 Specimen Preparation:7.2.1 Thermal Press, for compression-molding of plaques,and capable of obtaining temperatures, pressures and coolingrates, as recommended for PE and PP in Practice D4703 and inSection 11 of this test method.7.2.2 Flash Type
39、 Mold, picture-frame type, described inPractice D4703: stainless-steel chase to mold test plaques,uncoated polyester film parting sheets, and smooth, stainlesssteel backing plates of minimum 2.5 mm thickness.NOTE 8Injection molding apparatus have also been employed, inplace of the thermal press and
40、flash mold.NOTE 9One laboratory has prepared plaques using standard, steel dies(designed for preparing briquettes of powder materials) in a hydraulicpress. Aluminum pressing caps served as molds. The loaded die washeated in an oven for$2 h prior to pressing. During pressing, a laboratoryvacuum was d
41、rawn on the side port of the die. In the press, the pressurewas rapidly increased to 12 tons and the die was allowed to cool to roomtemperature. The pressing cap was removed from the cooled plaque.7.3 SpectrometerRequirements for a wavelength-dispersive XRF spectrometer are outlined in Guides C1118
42、andE1621.7.3.1 Source of X-ray Excitation, capable of exciting therecommended lines listed in Table 3, typically an X-ray tube.7.3.2 X-ray Detectors, with sufficient sensitivity to detectthe recommended lines listed in Table 3. Typical spectrometersinclude proportional counters, sealed or flow desig
43、ns, and ascintillation counter.7.3.3 Signal conditioning and data handling electronics t-hat include the functions of X-ray counting and peak process-ing.7.3.4 Vacuum PumpThe X-ray optical path must beevacuated using a mechanical pump.7.3.5 The following spectrometer features and accessoriesare opti
44、onal.7.3.5.1 Beam FiltersUsed on the primary X-ray beam tomake the excitation more selective and to reduce backgroundcount rates.7.3.5.2 Specimen SpinnerUse is recommended to reducethe effect of surface irregularities of the specimen.7.4 Drift Correction Monitor(s)Due to instability of themeasuremen
45、t system, the sensitivity and background of thespectrometer may drift with time. Drift correction monitorsmay be used to correct for this drift. The optimum driftcorrection monitor specimens are permanent materials that arestable with time and repeated exposure to X rays.NOTE 10Suitable drift correc
46、tion monitors can be fused bead speci-mens containing the relevant elements or elements that have fluorescencewith the same energies as the elements of interest. It is recommended thatmonitors provide count rates near to the low and high ends of the rangestypically encountered from plastic specimens
47、.7.5 GlovesDisposable cotton gloves are recommended forhandling all specimens to minimize contamination.7.6 Personal Protective EquipmentAppropriate personalprotective equipment for the handling of reagents and hotequipment.8. Reagents and Materials8.1 P-10 Gas, a mixture of 90 % argon and 10 % meth
48、ane,ultra-high purity or equivalent, for use with gas-flow propor-tional detectors.8.2 Nitrogen, prepurified grade or equivalent, for purgingthe melt fusion chamber.8.3 Elemental StandardsCompounds or additives, orboth, to be melt homogenized into polymer calibration stan-dards. Materials must have
49、reliable elemental assays or knownstoichiometry prior to use.NOTE 11One laboratory has prepared polymer calibration standardsby dissolving organometallic compounds in xylenes and adding knownamounts to low density polyethylene dissolved in xylenes in TFE-flurocarbon beakers at 100C with stirring. After removal of the solvents,the solids were ground in an ultracentrifugal mill and melt pressed.9. Reference Materials9.1 Users can prepare reference materials in house. Atechnique that offers consistent elemental dispersion through-out the calibration standard m
