1、Designation: D6953 18Standard Test Method forDetermination of Antioxidants and Erucamide Slip Additivesin Polyethylene Using Liquid Chromatography (LC)1This standard is issued under the fixed designation D6953; the number immediately following the designation indicates the year oforiginal adoption o
2、r, 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. Scope*1.1 This test method covers a liquid-chromatographic pro-cedure for the separatio
3、n of primary and secondary antioxidantand slip additives currently used in polyethylene plastics.These additives are extracted with either isopropanol (resindensities 0.94g/cm3) prior to liquid-chromatographic separation. The ultra-violet absorbance of the eluting compound(s) is measured andquantita
4、tion is performed using external calibration.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility o
5、f the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.Specific precautionary statements are given in Section 9.NOTE 1There is no known ISO equivalent to this standard.1.4 This internat
6、ional standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Comm
7、ittee.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD1600 Terminology forAbbreviated Terms Relating to Plas-ticsD4697 Guide for Maintaining Test Methods in the UsersLaboratory (Withdrawn 2009)3E131 Terminology Relating to Molecular SpectroscopyE169 Practices for Gen
8、eral Techniques of Ultraviolet-VisibleQuantitative AnalysisE275 Practice for Describing and Measuring Performance ofUltraviolet and Visible SpectrophotometersE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1657 Practice for Testing Variable-Wavelength
9、 Photomet-ric Detectors Used in Liquid ChromatographyIEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI): The Modern Metric System3. Terminology3.1 Definitions:3.1.1 For definitions of plastic terms and detector terminol-ogy used in this test method, see Terminologies D883, D16
10、00,and E1657.3.1.2 For units and symbols used in this test method, refer toTerminology E131 or IEEE/ASTM SI 10.4. Summary of Test Method4.1 The polyethylene sample is ground to a 1-mm (20mesh) or 0.5-mm (40 mesh) particle size and extracted byrefluxing with either isopropanol or cyclohexane.4.2 The
11、solvent extract is analyzed by liquid chromatogra-phy.4.3 Additive concentrations are determined from externalcalibration curves using reverse phase chromatography (C-8 orC-18 column) with ultraviolet (UV) detection at wavelengthscorresponding to the wavelengths of an absorption apex ofeach additive
12、 (except erucamide which does not have anabsorption maximum in the accessible UV region).5. Significance and Use5.1 Separation and identification of stabilizers used in themanufacture of polyethylene resins are necessary in order tocorrelate performance properties with polymer composition.1This test
13、 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 Nov. 1, 2018. Published November 2018. Originallyapproved in 2003. Last previous edition approved in 2011 as D6953 - 11.DOI:10.152
14、0/D6953-18.2For 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.3The last approved version of this historical stan
15、dard is referenced onwww.astm.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized
16、principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1This test method provides a means to determine the polymeradditives li
17、sted in Table 1 in polyethylene samples. This testmethod is capable of the determination of other antioxidants,but the stability of these during extraction has not beeninvestigated.5.2 The additive extraction procedure is made effective bythe relatively low solubility of the polymer sample in solven
18、tsgenerally used for liquid chromatographic analysis. In thismethod, isopropanol and cyclohexane were chosen because oftheir excellent extraction efficiencies as well as for safetyreasons. Other solvents including ethylacetate, isobutanol,chloroform and methylene chloride can also be used.5.3 Method
19、s other than refluxing that have been used toremove additives from the polymer matrix including pressur-ized liquid, microwave, ultrasonic, and supercritical fluidextractions. For the separation of the extracted additives, SFCand GC have been used successfully for several of theadditives.5.4 Under o
20、ptimum conditions, the lowest level of detectionfor an antioxidant is approximately 2 ppm.6. Interferences6.1 Any material eluting at or near the same retention timeas the additive can cause erroneous results. This includesdegradation products of the additives.6.2 A major source of interferences can
21、 be from solventimpurities. For this reason, the solvents shall be examined byHPLC using the same analysis conditions as for the samples(see Section 12).6.3 The grinding process may cause a low bias. Forexample, some erucamide slip is known to be lost to thegrinder surface and excessive grinding may
22、 cause degradationof the antioxidants.7. Apparatus7.1 Liquid Chromatograph, equipped with a multiple wave-length (see Practices E169 and E275) or photodiode arrayultraviolet detector, heated column compartment, and gradientelution capabilities. The liquid chromatograph shall beequipped with a means
23、for a 10-L injection such as a sampleloop.7.2 Chromatographic Column, C-8 or C-18 reverse phase,5-m particle size, 15 cm by 4.6 mm or equivalent, capable ofseparating the additives and their degradation products.7.3 Data Acquisition/Handling System, providing the meansfor determining chromatographic
24、 peak areas and for handlingand reporting data. This is best accomplished using a computerwith appropriate software.7.4 MillCutting Mill or Centrifugal Grinding Mill,equipped with 1-mm (20 mesh) and 0.5-mm (40 mesh)screens.7.5 Reflux Extraction Apparatus, consisting of a condenser,(24/40 ground-glas
25、s joint), a round-bottom 125-mL flaskhaving a 24/40 ground-glass joint, and a heating mantle.7.6 Boiling Chips.7.7 Filter System, (PTFE ), for non-aqueous solutions (poresize of 0.22 m).7.8 Analytical Balance, capable of weighing to 60.0001 g.7.9 Top Loading Balance, capable of weighing to 60.01 g.8
26、. Reagents and Materials8.1 Solvents:8.1.1 IsopropanolHPLC grade, spectro-quality or chro-matography quality reagent.8.1.2 CyclohexaneHPLC grade, spectro-quality or chro-matography quality reagent.8.1.3 WaterHPLC, or UV quality reagent, degassed bysparging with high-purity helium or by filtration un
27、dervacuum.8.1.4 AcetonitrileHPLC, spectro-quality or chromatogra-phy quality reagent (a reagent whose UV cutoff is about 190nm).8.2 Additives:8.2.1 High purity additives and degradation products (seeTable 1).9. Precautions9.1 Isopropanol and cyclohexane are flammable. This ex-traction procedure shou
28、ld be carried out in a fume hood.TABLE 1 Common Polyolefin AdditivesChemical Name ChemicalFormulaClassification CAS NumberBHEB, 2,6-di-t-butyl-4-ethylphenol or butylated hydroxyethylbenzeneC16H26O 1 Antioxidant 4130-42-1BHT, 2,6-di-t-butylcresol or butylated hydroxy toluene C15H24O 1 Antioxidant 128
29、-37-0Tris (2,4-di-t-butylphenyl)-phosphite C42H63O3P 2 Antioxidant 31570-04-4Tris(2,4-di-t-butylphenyl)-phosphate C30H39O4P Degradation product 78-33-1Tetrakismethylene(3,5-di-t-butyl-4- hydroxyhydrocinnamate)methaneC73H108O121 Antioxidant 6683-19-8Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)- propi
30、onate C35H62O31 Antioxidant 2082-79-32,2-ethylidene bis(4,6-di-t-butylphenol) C30H46O21 Antioxidant 35958-30-6ErucamideCis-13-docosenamide C28H43NO Fatty acid amide, slip agent 112-84-5TNPP,Tris(nonylphenyl)phosphite C45H69O3P 2 Antioxidant 26523-78-4Nonylphenol C15H24O 2 Antioxidant 104-40-5Tris(no
31、nylphenyl)phosphate C45H69O4P Degradation product 26569-53-9D6953 18210. Preparation of Solutions10.1 Polymer Samples:10.1.1 Grind the sample to a particle size of 1 mm, that is,20 mesh (density 0.94 g/cm3).NOTE 2Unless sample amount is limited, grind a minimum of 10 g.It is important to minimize th
32、e time of grinding to prevent any thermaldegradation of the additives in the polymer. Some erucamide is known tobe lost during grinding.NOTE 3A cutting-type mill is needed for film samples. Because of itshigher efficiency, a centrifugal-type mill is recommended for pelletsamples.10.1.2 Weigh, to the
33、 nearest 0.01 g, approximately5gofthesample, that is, Wsample, into a pre-weighed (to the nearest 0.01g) 125-mL flat-bottom flask containing boiling chips, that is,Wflask. Add approximately 50.0 mL of isopropanol or cyclo-hexane and boil for a minimum of 2 h.NOTE 4Isopropanol is used as the extracti
34、on solvent for densities ofless than 0.94 g/cm3and cyclohexane for densities higher than 0.94 g/cm3.10.1.3 Cool the solution to room temperature by raising theflask from the heating mantle while still attached to thecondenser.10.1.4 Weigh the cooled flask to the nearest 0.01 g, that is,W(flask + sol
35、).10.1.5 Attach a filter disk assembly to a 5-mL Luer-Lok tiphypodermic syringe.10.1.6 Decant approximately 4 mL of the solvent extractinto the above syringe.10.1.7 Insert the plunger and carefully apply pressure toforce the solvent extract through the filter into a sample vial.10.1.8 Calculate the
36、amount (mg) of sample per kg ofsolution, Samplesol:Sample#sol5106WsampleWflask1sol!2 Wflask!(1)10.2 Concentrated Additive Standards:10.2.1 Prepare two to three mixtures in 125-mL septumbottles by weighing the bottles, including septum and cap, tothe nearest 0.1 mg.10.2.2 Weigh into a bottle, to the
37、nearest 0.1 mg, approxi-mately 0.2 g of each additive.10.2.3 Fill the bottle with either isopropanol orcyclohexane, cap and weigh the bottle on a top loading balanceto the nearest 10 mg.10.2.4 Agitate the bottle to speed up dissolution.10.2.5 Calculate the concentration, Additiveconc, of eachadditiv
38、e in the concentrated standard in mg/kg (that is, ppm) asfollows:Additive#conc5106WaddWTadd1Wsol!(2)where:Wadd= weight (g) of individual additive,WTadd= total weight (g) of all additives, andWsol= weight (g) of solvent.10.3 Dilute Additive Standards:10.3.1 Prepare four dilute standards of each conce
39、ntratedstandard by weighing 30-mL septum bottles, including septumand cap, to the nearest 0.1 mg.10.3.2 Add with a 5-mL syringe, 0.5 mL, 1.0 mL, 2.0 mL,and 5.0 mL of a concentrated solution to each of four of the30-mL bottles and weigh to the nearest 0.1 mg.10.3.3 Fill the bottles with isopropanol o
40、r cyclohexane, cap,mix and weigh to the nearest 1 mg.10.3.4 Calculate the concentration, Additivedil, of eachadditive in the dilute standards in mg/kg (that is, ppm) asfollows:Additive#dil5WconcAdditive#concWconc1Wsol!(3)where:Wconc= weight (g) of concentrated standardsolution,Additiveconc= concentr
41、ation (mg/kg) of additive in con-centrated standard (see 10.2.5), andWsol= weight (g) of solvent used for dilution.11. Performance Requirements11.1 ResolutionThe resolution (R) provides an indicationof the component separation and band broadening of a column.For Gaussian-shaped peaks, the resolution
42、 is defined as:R 52tR,22 tR,1!W11W2!(4)where:tR,1,tR,2= peak elution time in minutes of Additives 1 and2, andW1,W2= peak width in minutes of Additives 1 and 2determined by measuring the distance betweenthe baseline intercepts of lines drawn tangent tothe peak inflection points.11.1.1 For an extracte
43、d additives mixtures containing anycombination (including degradation products) of those listed inTable 1, the resolution of any two peaks measured at a singlewavelength must be greater than one, that is, R 1. For peakswith R 1, two wavelengths are needed to measure the twocomponents (see 15.2).NOTE
44、 5A resolution of R = 1 represents a peak overlap of approxi-mately 3 %.11.2 Plate Count NumberA 10-cm column packed with5-m particles is expected to have a plate count in excess of60 000 plates calculated in accordance with the followingexpression:N 5 16StRWD2(5)where:tR= peak elution time in minut
45、es, andW = peak width in minutes as determined as outlined inSection 11.11.2.1 No minimum number is required as long as theresolution requirement of 11.1 is met.D6953 18312. Preparation of Liquid Chromatograph12.1 Flow Rate2.0 mL/min.12.2 Mobile Phase Gradient:12.2.1 Initial Mobile Phase60 % acetoni
46、trile and 40 %water.12.2.2 Final Mobile Phase Condition100 % acetonitrileand 0 % water.12.2.3 Gradient Length6 min.12.2.4 Gradient CurveLinear.12.2.5 Hold at 100 % acetonitrile and 0 % water for 3 min.12.2.6 Return to 60 % acetonitrile and 40 % water at 9 minat a flow rate of 2 mL/min for 4 min.NOTE
47、 6The flow rate and gradient conditions listed in 12.1 and 12.2have been used successfully with a 15-cm by 4.6-mm column packed with5-m C-8 reverse phase particles (see Fig. 1). The optimum flow rate (thatis, 1.0 to 2.0 mL/min) and the exact gradient will depend on the columnused and the additive fo
48、rmulations typically analyzed (see Section 11 forperformance requirements).12.3 DetectorUltraviolet detector with a range setting ofabout 0.1 AUFS at the following wavelengths:200 nm for erucamide slip210 nm for CAS 78-33-1217 nm for TNPP and its degradation products270 nm for CAS 31570-04-4280 nm f
49、or BHEB, BHT, CAS 6683-19-8. CAS 2082-79-3, and CAS35958-30-6NOTE 7Erucamide does not have an absorption peak in the accessibleUV region. The absorption at 200 nm represents the tailing end of anabsorption peak at a wavelength of less than 190 nm. Because of the steepslope of the shoulder, a wavelength precision of better than 1 nm is neededto avoid unacceptable fluctuations in detector response (that is, extinctioncoefficient). Frequent injections of an erucamide standard are recom-mended.12.4 ColumnC-8 or C-18 reverse
