1、Designation: D 4526 96 (Reapproved 2001)e1Standard Practice forDetermination of Volatiles in Polymers by Static HeadspaceGas Chromatography1This standard is issued under the fixed designation D 4526; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase 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.e1NOTESeveral sections were changed and added editorially in March 2001.1. Scope1.1 Headspace gas ch
3、romatography (GC) involves the de-termination of volatile components in a polymer solution bygas chromatography of a vapor phase in thermal equilibriumwith the sample matrix. Volatiles in finely ground insolublepolymers can also be determined with and without an extract-ing solvent.1.2 This practice
4、 provides two procedures:1.2.1 Procedure AAutomatic headspace analysis.1.2.2 Procedure BManual injection headspace analysis.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 standard to establish appr
5、o-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in Section 6.NOTE 1There is no equivalent ISO standard.2. Referenced Documents2.1 ASTM Standards:D 4322 Test Method for Residual Acrylonitrile Mo
6、nomer inStyrene-Acrylonytrile Copolymers and Nitrile Rubber byHeadspace Gas Chromatography2E 260 Practice for Packed Column Gas Chromatography3E 355 Practice for Gas Chromatography Terms and Rela-tionships3E 594 Practice for Testing Flame Ionization Detectors Usedin Gas Chromatography33. Significanc
7、e and Use3.1 For various reasons, one may want to measure the levelof unreacted or residual monomer, water, or other volatilecomponents in a polymer sample.3.2 Volatiles of interest are often at trace concentrations.Headspace analysis is suited for determination of these tracecomponents which often
8、cannot be determined by conventionalgas chromatography because of sample decomposition orinterferences.3.3 For polymer analysis, sample treatment for headspaceanalysis is simpler than conventional gas chromatography,where precipitation steps may be required to prevent polymercontamination of the chr
9、omatographic column.3.4 This headspace practice will be able to determinequalitatively any component with sufficient vapor pressure. Itis capable of yielding semiquantitative results and can be usedfor relative comparisons between samples.4. Apparatus4.1 Gas Chromatograph, equipped with an appropria
10、tedetector and backflush valve.4.1.1 For Procedure A, an Automated Headspace Sampler,4including backflush capability, thermostated sample tray, andassociated accessories fulfill these requirements while provid-ing for automatic sequential sampling of headspace vapors.4.1.2 Procedure B requires the f
11、ollowing additional equip-ment:4.1.2.1 Constant-Temperature Bath, capable of maintaining90 6 1C.4.1.2.2 Gas-Tight Gas Chromatographic Syringes, whichcan be heated to 90C for sampling and injection.4.1.2.3 Valve, 6-port for backflush assembly.NOTE 2Appropriate detectors could include the following:(a
12、) Flame ionization (FID) for general organic volatiles,(b) Electron capture (EC) for halogenated species,(c) Nitrogen-phosphorous (NPD) for acrylonitrile,(d) Thermal conductivity (TC) for water, and(e) Hall electroconductivity or photoionization (PID) for vinyl chlo-ride.4.2 Chromatographic Columns:
13、1This practice is under the jurisdiction of ASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved Nov. 10, 1996. Published May 1997. Originallypublished as D 4526 85. Last previous edition D 4526 85 (1991)e1.2Annual Book
14、of ASTM Standards, Vol 08.02.3Annual Book of ASTM Standards, Vol 14.01.4Available from Perkin-Elmer Corp., Main Ave., Norwalk, CT 06856.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2.1 Packed Column AnalysisColumn packings5found
15、to be useful for residual monomers (for example, acrylonitrile,vinyl chloride) include Chromosorb or Porapak porous poly-mer packings, 0.4 % Carbowax 1500 liquid phase on CarbopakC support, or 0.19 % picric acid on Carbopak C support. Othercolumns can be used after it is determined that they give th
16、erequired resolution and accuracy for the component of interest.4.2.2 Capillary Column AnalysisChoose a column ca-pable of achieving the required resolution for the componentsof interest. For example, for acrylonitrile monomer, the columnof choice is a Quadrex 0072, 25m 3 0.32mm internaldiameter fus
17、ed silica.64.3 Integrator, recorder (5mV full scale), computing inte-grator or appropriate computer data station and softwarecapable of measuring and storing peak area data.4.4 Headspace Vials, septa, ring closures, and vial sealer.4.5 Analytical Balance, capable of weighing to 60.0001 g.4.6 Soap Fi
18、lm Flowmeter and Stopwatch, or other means ofmeasuring gas flow rates.4.7 Pressure Regulators for all required gas cylinders.4.8 Filter-Dryer Assemblies for each required gas cylinder.5. Reagents and Materials5.1 Solvent, Reagent Grade, or Best AvailableThe solventshould be free of interferences at
19、the retention time of volatilecompounds determined by this technique. Typical polymersolvents include water, dimethylformamide (DMF), dimethy-lacetamide (DMAC), propylene carbonate, ando-dichlorobenzene. These solvents are readily backflushedfrom most chromatographic columns.NOTE 3Volatile contamina
20、nts can often be removed by sparging withan inert gas for 24 to 48 h.5.2 Nitrogen, oxygen-free.NOTE 4Helium may also be used as the carrier gas and argon/methaneis the preferred carrier gas for use with electron capture detectors.5.3 Hydrogen, prepurified, for use with flame ionizationdetectors.5.4
21、Air, breathing or water pumped, for use with flameionization or nitrogen-phosphorus detectors.5.5 Standards, best available, for volatile compounds to beanalyzed using this technique.6. Safety Precautions6.1 Volatiles such as vinyl chloride and acrylonitrile shouldnot be released to the laboratory a
22、tmosphere. Prepare standardsand handle samples in a well-ventilated fume hood.6.2 Some of the recommended solvents are flammable.Dimethylacetamide is also absorbed through the skin, so avoidcontact.6.3 Be careful not to come into contact with heated chro-matograph parts, such as the detector, column
23、, rotating sampletray, hot sample bottles, etc.6.4 Once heated, sample vials containing polymer volatilesare under pressure. After analysis, vent the pressure with ahypodermic syringe needle connected to a charcoal slug orvented hood before removing vials from the constant tempera-ture bath.7. Stora
24、ge and Sampling7.1 To prevent loss of volatiles from polymer pellets, orresin, store in tightly sealed jars with minimal headspace orheat-sealed pouches constructed of an outer polyester layer, analuminum foil middle layer, and a polyolefin inner sealinglayer.7.2 For rolled polymer film samples, dis
25、card 3 to5moffilmbefore taking the sample for headspace analysis becausevolatiles can be lost by diffusion through the outer film layers.7.3 Powdered resin samples (for example, poly(vinyl chlo-ride) can be weighed directly into a tared headspace vial. A4-g sample (weighed to the nearest 0.0001 g) s
26、hould beadequate for determination of many volatiles at the parts permillion (ppm) levels using sensitive ionization detectors.7.4 Polymer pellets or granules and film samples can bedissolved, depending on chemistry of polymer, to facilitateattaining thermal equilibrium in a reasonable period of tim
27、e.These samples are weighed (0.56 0.001 g) into headspacevials, then dissolved in 10 mL of an appropriate solvent. Usingionization detection, these 5 % solutions provide sensitivity formany volatiles at ppm levels. Sample size can be increased toattain sensitivity at lower levels.NOTE 5Freeze grindi
28、ng polymer pellets or granules with liquidnitrogen and screening through a thirty-mesh screen often works as wellas testing powdered resin. However, some volatiles may be lost even atthese low temperatures.NOTE 6This technique of sample preparation requires analysis of thesolvent blank to ensure fre
29、edom from interferences at volatile componentretention times.NOTE 7Increased sample sizes can result in viscous solutions. Warm-ing these solutions is often necessary to ensure complete sample dissolu-tion.8. Preparation of the Gas Chromatograph8.1 Refer to Recommended Practice E 260 and the operato
30、rand service manuals of the instrument being used for detailsregarding column installation, flow rate adjustment, and opti-mization of detector sensitivity.8.2 Refer to Practices E 355 and E 594 for information onterms, relationships, and procedures for testing flame ioniza-tion detectors.8.3 Instal
31、l the chromatographic column in the instrumentoven. If solvent backflush is to be used, the front portion of thecolumn consists of a short length (3 ft) connected with a lowdead volume tee to the longer analytical column section. Fig. 1shows a typical backflush assembly for a gas chromatographdesign
32、ed for manual headspace analysis.8.4 Adjust the carrier gas flow rate to obtain the samecolumn flow in the analysis and backflush chromatographicmodes.8.5 Switch off the detector combustion gases before discon-necting the column from the detector to avoid buildup of anexplosive gas mixture in the GC
33、 oven.5Available from Supelco, Inc., P.O. Box 628, 146 S. Water St., Bellefonte, PA16823.6Available form Quadrex Corp., P.O. Box 3881, Woodbridge, CT 06525.D 452628.6 Condition the column at a temperature that is 10 to 20Cabove the expected operating temperature. With ionizationdetectors, the column
34、 should not be connected to the detectorduring the overnight conditioning period.8.7 After conditioning, connect the column to the detectorand optimize detector gas flow (air, hydrogen) for maximumsensitivity.8.8 Set temperatures as follows:8.8.1 Chromatograph Oven (Column), as appropriate.8.8.2 Dos
35、ing Needle, 10C above column temperature.8.8.3 Injection Block, 10C above column temperature.8.8.4 Detector, 10C above column temperature.8.8.5 Temperature Bath, 90 to 120C (depending on com-ponent volatility and rated bath temperature).9. Procedures9.1 Procedure AAutomated Sample Analysis:9.1.1 Pre
36、pare sample solutions in accordance with thecriteria of Section 7, then equilibrate solutions for at least 1 hin the thermostatted sample tray.9.1.2 Optimize analyzer injection time to give maximumsignal. Injection times from 6 to 9 s are suitable for mostdeterminations at the ppm level.9.1.3 Adjust
37、 the analysis and backflush times consistentwith fast analysis time and freedom from solvent interferences.9.2 Procedure BManual Injection:9.2.1 Prepare sample solutions in accordance with thecriteria of Section 7, then equilibrate solutions for at least 1 hin a constant-temperature bath.9.2.2 Using
38、 a warm gas syringe, inject 1.0 mL of theequilibrated sample headspace into the gas chromatographprepared in Section 8.NOTE 8The syringe can be kept warm in a 90C oven betweensamplings.9.2.3 Switch backflush valve to VENT position 1 min afterelution of the latest volatile component of interest. Back
39、flushtime should be four times as long as the forward flow time.9.2.4 At the end of the predetermined backflush time, returnthe valve to the ANALYSIS position.FIG. 1 Typical 6-Port Valve Backflush AssemblyD 452639.2.5 Allow at least 2 min for baseline equilibration be-tween samples.10. Report10.1 Re
40、port the following information:10.1.1 Sample identification,10.1.2 Sample preparation; equilibration time and tempera-ture,10.1.3 Method of calibration, and10.1.4 Concentration of desired volatile components.11. Keywords11.1 gas chromatography; headspace; polymers; volatilesSUMMARY OF CHANGESCommitt
41、ee D20 has identified the location of selected changes to this standard since the last issue(D 4526 - 96) that may impact the use of this standard.(1) Five year review with editorial changes.ASTM International takes no position respecting the validity of any patent rights asserted in connection with
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