1、Designation: D6953 11Standard 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 and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in Section 9.NOTE 1There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM
6、 Standards:2D883 Terminology Relating to PlasticsD1600 Terminology for Abbreviated Terms Relating toPlasticsD4697 Guide for Maintaining Test Methods in the UsersLaboratory3E131 Terminology Relating to Molecular SpectroscopyE169 Practices for General Techniques of Ultraviolet-Visible Quantitative Ana
7、lysisE275 Practice for Describing and Measuring Performanceof Ultraviolet and Visible SpectrophotometersE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1657 Practice for Testing Variable-Wavelength Photomet-ric Detectors Used in Liquid ChromatographyI
8、EEE/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, D1600,and E1657.3.1.2 For units and symbols used in this
9、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 solvent extract is analyzed by liquid chromatogra-phy.
10、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 (except erucamide which does not have anabsorption ma
11、ximum 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.This test method provides a means to determine the polymeradditi
12、ves listed 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
13、solventsgenerally used for liquid chromatographic analysis. In this1This 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 Sept. 1, 2011. Published September 2011. Originallyap
14、proved in 2003. Last previous edition approved in 2003 as D6953 - 03.DOI:10.1520/D6953-11.2For 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 Sum
15、mary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1*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 St
16、ates.method, 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 Methods other than refluxing that have been used toremove addi
17、tives 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 optimum conditions, the lowest level of detectionfor an a
18、ntioxidant 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 be from solventimpurities. For this reason, the solvent
19、s 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. For ex-ample, some erucamide slip is known to be lost to the grindersurface and excessive grinding may cause degradation of theantioxidants.7. Apparatus7.1
20、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 for a 10-L injection such as a sampleloop.7.2 Chromato
21、graphic 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 peak areas and for handlingand reporting data. This i
22、s best accomplished using a computerwith appropriate software.7.4 MillCutting Mill (Wiley) or Centrifugal Grinding Mill(Brinkmann), 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-glass joint), a round-bottom 125-mL fl
23、askhaving 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. Reagents and Materials8.1 Solven
24、ts: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 undervacuum.8.1.4 AcetonitrileHPLC,
25、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 should be carried out in a fume hood.1
26、0. 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. Itis important to minimize the time of grinding to prevent any thermaldegradation of the additives
27、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 nearest 0.01 g, approximately5gofthesample, that is, Wsample, into a
28、pre-weighed (to the nearest 0.01TABLE 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)- propio
30、nate 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(non
31、ylphenyl)phosphate C45H69O4P Degradation product 26569-53-9D6953 112g) 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 extraction solvent for densities ofless th
32、an 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).10.1.5 Attach a filter disk asse
33、mbly 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 amount (mg) of sample per kg ofsol
34、ution, Samplesol:Sample#sol5106WsampleWflask 1 sol!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 nearest 0.1 mg, approxi-mately 0
35、.2 g of each additive.10.2.3 Fill the bottle with either isopropanol or cyclo-hexane, cap and weigh the bottle on a top loading balance tothe nearest 10 mg.10.2.4 Agitate the bottle to speed up dissolution.10.2.5 Calculate the concentration, Additiveconc, of eachadditive in the concentrated standard
36、 in mg/kg (that is, ppm) asfollows:Additive#conc5106WaddWTadd1 Wsol!(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 concentratedstandard by weighing 3
37、0-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 or cyclohexane, cap,mix and we
38、igh 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#concWconc1 Wsol!(3)where:Wconc= weight (g) of concentrated standard solu-tion,Additiveconc= concentration (mg/kg) of additive
39、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 is defined as:R 52tR,22 t
40、R,1!W11 W2!(4)where:tR,1,tR,2= peak elution time in minutes of Additives 1and 2, andW1,W2= peak width in minutes of Additives 1 and 2determined by measuring the distance betweenthe baseline intercepts of lines drawn tangentto the peak inflection points.11.1.1 For an extracted additives mixtures cont
41、aining 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 5A resolution of R = 1
42、 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 minutes, andW = peak width i
43、n 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.12. Preparation of Liquid Chromatograph12.1 Flow Rate2.0 mL/min.12.2 Mobile Phase Gradient:12.2.1 Initial Mobile Phase60 % acetonitrile and 40 %water.12.2.2 Final
44、 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 6The flow rate and gradient con
45、ditions 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 columnD6953 113used and the additive formulations typically an
46、alyzed (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 for BHEB, BHT, CAS 6683-
47、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
48、 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 phase, 5-m particlesize, 15 cm by 4.6 mm or equivalent.12.5 TemperatureA column temperature of be
49、tween 50Cand 60C is suggested.12.6 Sample Size10 L.13. Calibration13.1 Identify the retention time of each additive/degradationproduct by referring to Fig. 1 or by injecting single componentsolutions.13.2 Inject 10 L of each of the four dilute standardmixtures prepared in 10.3 into the liquid chromatographsystem.13.3 Measure the peak areas using a computer or anintegrator.13.4 Plot peak areas versus concentration for each additiveand fit the points to a linear regression line. This line shall havea zero intercept,
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