1、Designation: D 6953 03Standard Test Method forDetermination of Antioxidants and Erucamide Slip Additivesin Polyethylene Using Liquid Chromatography (LC)1This standard is issued under the fixed designation D 6953; the number immediately following the designation indicates the year oforiginal adoption
2、 or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a liquid-chromatographic pro-cedure for the separat
3、ion of some additives currently used inpolyethylene. These additives are extracted with either isopro-panol (resin densities 0.94 g/cm3) prior to liquid-chromatographic sepa-ration. The ultraviolet absorbance of the eluting compound(s)is measured and quantitation is performed using externalcalibrati
4、on.1.2 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 standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific pr
5、ecau-tionary statements are given in Section 9.NOTE 1There is no equivalent ISO standard.2. Referenced Documents2.1 ASTM Standards:D 883 Terminology Relating to Plastics2D 1600 Terminology for Abbreviated Terms Relating toPlastics2D 4697 Guide for Maintaining Test Methods in the UsersLaboratory3E 13
6、1 Terminology Relating to Molecular Spectroscopy4E 169 Practices for General Techniques of Ultraviolet-Visible, and Near-Infrared Spectrophotometers4E 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near-Infrared Spectrophotom-eters4E 691 Practice for Conducting an
7、Interlaboratory Study toDetermine the Precision of a Test Method5E 1657 Practice for Testing Variable-Wavelength Photomet-ric Detectors Used in Liquid Chromatography4IEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI): The Modern Metric System3. Terminology3.1 Definitions:3.1.1
8、 For definitions of plastic terms and detector terminol-ogy used in this test method, see Terminologies D 883, D 1600,and E 1657.3.1.2 For units and symbols used in this test method, refer toTerminology E 131 or IEEE/ASTM SI 10.3.2 Additives:3.2.1 BHEB, Prodox 5002,6-di-t-butyl-4-ethylphenol orbutyl
9、ated hydroxyethyl benzene, CAS No. 4130-42-1.3.2.2 BHT, CAO-3, Noclizer M-172,6-di-t-butylcresol orbutylated hydroxy toluene, CAS No. 128-37-0.3.2.3 Irgafos 168Tris(2,4-di-t-butylphenyl)-phosphite,CAS No. 31570-04-4.3.2.3.1 Oxidized Irgafos 168Tris(2,4-di-t-butylphenyl)-phosphate.3.2.4 Irganox 1010T
10、etrakismethylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate) methane CAS No. 6683-19-8.3.2.5 Irganox 1076Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate, CAS No. 2082-79-3.3.2.6 Isonox 1292,2-ethylidene bis(4,6-di-t-butylphenol), CAS No. 112-84-5.3.2.7 Kemamide-E, ErucamideCis-13-docosenamide,CA
11、S No. 112-84-5.3.2.8 TNPP, Weston 399Tris(nonylphenyl)phosphite,CAS No. 26523-78-4.3.2.8.1 Hydrolyzed TNPPNonylphenol, CAS No. 104-40-5.3.2.8.2 Oxidized TNPPTris(nonylphenyl)phosphate, CASNo. 26569-53-9 (available in small quantities from GE Spe-cialty Chemicals as XR2616).4. Summary of Test Method4
12、.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.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is
13、 the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved July 10, 2003. Published August 2003.2Annual Book of ASTM Standards, Vol 08.01.3Annual Book of ASTM Standards, Vol 07.02.4Annual Book of ASTM Standards, Vol 03.06.5Annual Book of ASTM Standards, Vol 14.0
14、2.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3 Additive concentrations are determined from externalcalibration curves using reverse phase chromatography (C-8 orC-18 column) with ultraviolet (UV) detection at wavelengthscorresp
15、onding to the wavelengths of an absorption apex ofeach additive (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 tocorre
16、late performance properties with polymer composition.This test method provides a means to determine BHT, BHEB,Isonox 129, erucamide slip, Irgafos 168, Irganox 1010, Irganox1076 and TNPP levels in polyethylene samples. This testmethod should be applicable for the determination of otherantioxidants su
17、ch as Ultranox 626, Ethanox 330, Santanox R,and Topanol CA, but the stability of these during extraction hasnot been investigated.5.2 The additive extraction procedure is made effective bythe relatively low solubility of the polymer sample in solventsgenerally used for liquid chromatographic analysi
18、s. 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 Methods other than refluxing that have been used toremove
19、 additives from the polymer matrix include microwave,ultrasonic, and supercritical fluid extractions. For the separa-tion of the extracted additives, SFC and GC have been usedsuccessfully for several of the additives.5.4 Under optimum conditions, the lowest level of detectionfor an antioxidant is ap
20、proximately 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 solvents should be exam
21、ined 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 Liquid Chromato
22、graph, equipped with a multiple wave-length (see Practices E 169 and E 275) or photodiode arrayultraviolet detector, heated column compartment, and gradientelution capabilities. The liquid chromatograph should beequipped with a means for a 10-L injection such as a sampleloop.7.2 Chromatographic Colu
23、mn, 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 is best accom
24、plished 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 flaskhaving a
25、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 Solvents:8.1.1 Iso
26、propanolHPLC 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, spectro-qual
27、ity 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 (see3.2).9. Precautions9.1 Isopropanol and cyclohexane are flammable. This ex-traction procedure should be carried out in a fume hood.10. Preparation o
28、f 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 in the polymer.
29、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 pre-weighed (to
30、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 extraction solvent for densities ofless than 0.94 g/cm3and cyclohexane for densities higher th
31、an 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).D695303210.1.5 Attach a filter disk assembly to a 5-mL Luer-Lok tiphypodermic syring
32、e.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 ofsolution, Samplesol:Sample#sol5106WsampleWflask
33、 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 0.2 g of each additive.10.2.3 Fill the bottle
34、 with either isopropanol or cyclohex-ane, cap and weigh the bottle on a top loading balance to thenearest 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 in mg/kg (that is, ppm) asfollows:Additive#
35、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 30-mL septum bottles, including septumand cap
36、, 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 weigh to the nearest 1 mg.10.3.4 Calculate the
37、 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 in con-centrated standard (see 10.2.5), andW
38、sol= 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 tR,1!W11 W2!(4)where:tR,1,tR,2= peak elution
39、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 containing anycombination (including degradation
40、 products) of those listed in3.2, 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 represents a peak overlap of approxi-mately 3 %
41、.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 in minutes as determined as outlined inSection 11
42、.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 Mobile Phase Condition100 % acetonitrileand 0 %
43、 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 conditions listed in 12.1 and 12.2have been used su
44、ccessfully 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 formulations typically analyzed (see Section 11 forperformance requirements).12.3
45、DetectorUltraviolet detector with a range setting ofabout 0.1 AUFS at the following wavelengths:200 nm for erucamide slip210 nm for oxidized Irgafos 168217 nm for TNPP and its degradation products270 nm for Irgafos 168280 nm for BHEB, BHT, Irganox 1010, Irganox 1076 and Isonox 129NOTE 7Erucamide doe
46、s 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
47、 detector response (that is, extinctionD6953033coefficient). 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 between 50Cand 60C is suggested.12.6 Sample Size10
48、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
49、 computer or anintegrator.13.4 Plot peak areas versus concentration for each additiveand fit the points to a linear regression line. This line shouldhave a zero intercept, that is, the general equation for theregression line should be A = kC, where A is the peak area ofthe additive in the standard, k is the slope of the regression line,and C is the solution concentration of the additive.14. Procedure14.1 Use liquid chromatographic conditions as prescribed inSection 12.14.2 Inject 10 L of each sample solution and, wit
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