1、Designation: F 2013 05Standard Test Method forDetermination of Residual Acetaldehyde in PolyethyleneTerephthalate Bottle Polymer Using an Automated StaticHead-Space Sampling Device and a Capillary GC with aFlame Ionization Detector1This standard is issued under the fixed designation F 2013; the numb
2、er immediately following the designation indicates the year oforiginal adoption 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. Scope
3、1.1 This test method covers a gas chromatographic proce-dure for the determination of the ppm residual acetaldehyde(AA) present in poly(ethylene terephthalate) (PET) homo-polymers and co-polymers which are used in the manufactureof beverage bottles. This includes sample types of bothamorphous and so
4、lid-stated pellet and preform samples, asopposed to the bottle test, Test Method D 4509, an acetalde-hyde test requiring 24 h of desorption time at 23C into thebottle headspace and then the concentration of the headspacequantified by a similar GC method.1.2 This standard does not purport to address
5、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.2. Referenced Documents2.1 ASTM Standards:2D 4509 Test Method
6、s for Determining the 24-Hour Gas(AIR) Space Acetaldehyde Content of Freshly Blown PETBottles3E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 The terms employed in this test method are commonlyused in normal laboratory practice and r
7、equire no specialcomment.4. Summary of Test Method4.1 A specified size (800 to 1000 m) of granulated sampleis weighed into a 20-mL head-space vial, sealed, and thenheated at 150C for 60 min. After heating, the gas above thesealed sample of PET polymer is injected onto a capillary GCcolumn. The aceta
8、ldehyde is separated, and the ppm ofacetaldehyde is calculated.5. Significance and Use5.1 This test method is of particular use as a quality controltool for a molding or synthesis operation. Acetaldehyde is avolatile degradation product generated during melt processingof PET. Thus, it becomes trappe
9、d in the sidewalls of a moldedarticle and desorbs slowly into the contents packaged therein.In some foods and beverages AA can impart an off-taste that isundesirable, thus, it is important to know its concentration inPET articles that are to be used in food contact applications.5.2 The desorption co
10、nditions of 150 C for 60 min are suchthat no measurable AA is generated by the sample during thedesorption process.6. Sources of Error6.1 Abias is known to exist if the ratio of sample mass (mg)to head-space vial volume (mL) exceeds a value of ten.6.2 Acetaldehyde is very volatile and must be handle
11、dcarefully to avoid sample loss during the calibration procedure.Storing the standard vials in a refrigerator is a must tominimize the error due to volatility.6.3 Failure to achieve a tight seal on the head-space vial willresult in the loss of acetaldehyde during storage and desorp-tion, producing a
12、 false low value.6.4 Failure to grind the sample to the appropriate particlesize may lead to a false low value for residual AA due to theincreased path length for desorption.6.5 Samples submitted for “residual AA measurement”should be stored in a freezer until they are tested. Failure to doso can re
13、sult in lower than expected results.1This test method is under the jurisdiction of ASTM Committee F02 on FlexibleBarrier Materials and is the direct responsibility of Subcommittee F02.15 onChemical/Safety Properties.Current edition approved April 1, 2005. Published September 2005. Originallyapproved
14、 in 2000 as published as F 201300. Last previous edition approved in2001 as F 201301.2For 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
15、page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.6 Excessive grinding of samples can cause residual AAcontained therein to be desorbed. Extensive excessive grindingcan lead to actual melting of the
16、 polymer and AA generation.Samples which have been chilled in liquid nitrogen properlyshould only be in the grinder for ;30 s or less.7. Apparatus7.1 Gas Chromatograph.7.2 Integrator.7.3 Head-Space Sampler.7.4 Column, 30-m by 0.53-mm inside diameter (megaborecapillary column).7.5 Vials, 20-mL, head-
17、space, with 20-mm septa, 20-mmaluminum caps, and crimper for 20-mm caps.7.6 Crimper, 20-mm.7.7 Decrimper, 20-mm.7.8 Wiley Mill, equipped with an 800 to 1000-m screen, orequivalent.7.9 Syringe, calibrated, with certificate of calibration.7.10 Small Vacuum Cleaner, with hose attachment forcleaning.7.1
18、1 Analytical Balance, capable of accurately weighing toat least 60.0001 g.7.12 Hammer.8. Reagents and Materials8.1 Acetaldehyde (AA), 500 ppm AA in water (or 1000ppm), purchased certified standard.8.2 Liquid Nitrogen, plant grade (R-3, S-3).9. Calibration and StandardizationNOTE 1The following proce
19、dure should be performed and recordedonce every three months.9.1 Break open a certified AA standard ampule (ampulesmust be stored in a refrigerator) or prepare AA standard by theattached supplemental procedure. (See Appendix X5.)9.2 Using the syringe, fill it by placing the tip in the liquidstandard
20、 and quickly moving the plunger up and down severaltime to evacuate any bubbles, then pull the plunger back pastthe 2.000-L mark to 2.200 to 2.250 L.9.3 Wipe the syringe needle with a tissue.9.4 Depress the plunger until the digital readout is 2.000 L.9.5 Smear the excess liquid that is on the syrin
21、ge tip on theOUTSIDE of the headspace vial.9.6 Place the syringe inside of the vial so that the tip justtouches the bottom of the vial.9.7 Quickly inject the liquid standard into the vial and swirlthe syringe tip around the inside of the vial to smear all liquidon the vial walls.9.8 Remove the syrin
22、ge and IMMEDIATELY cap the vial.9.9 Calculate the weight of AA based on the standardscertified value and a 2.000-L injection volume.NOTE 2Acetaldehyde is very volatile. The AA ampules must bestored in a refrigerator, and the standards prepared immediately afterbreaking open an ampule.9.10 Analyze th
23、e working standard by the procedure de-scribed in Section 11, starting with 11.2.11.9.11 Calculate an AA response factor for the standard usingthe following equation:response factor of AA 5 Wt of AA in g/area of AA (1)NOTE 3Due to the error associated with the certified standard,9.1-9.11 should be p
24、erformed five times using five different standardampules.9.12 Average the five response factors obtained, and use thisvalue for the sample analyses.9.13 Manually enter the calculated response factor in thecalibration list of the integrator or data system.NOTE 4During a series of sample analyses, a p
25、eriodic check ofinstrument performance is recommended by placing a few liquid standardsamples throughout the sample set. If these values fall out of theacceptable range as specified by the certificate of analysis, recalibration(9.1-9.12) should be performed.10. Sample Preparation10.1 Parisons or Pre
26、forms or PlaquesMay be cryogeni-cally ground whole, or can be broken into small pieces with ahammer (using liquid nitrogen) and then ground with the aid ofgrinding mill equipped with a 20-mesh or 850-m screen. Thegrind should be thoroughly homogenized before sampling forAA. If the appropriate size s
27、creen is not available on the largegrinding mill, then it is suggested that the sample be ground to3 to 6 mm on the large mill and the sample thoroughlyhomogenized. A portion can then be taken to a smaller millequipped with the 20-mesh or 850-m screen and cryogeni-cally ground again before analysis.
28、 Again the final sampleshould be thoroughly homogenized.10.2 PelletsMay be cryogenically ground in a smallgrinding mill using liquid nitrogen. The final sample should bethoroughly homogenized before sampling for analysis.NOTE 5Samples, either preforms, plaques, or pellets, should bechilled in the li
29、quid nitrogen for several minutes until the liquid nitrogenstops boiling and then dropped immediately into the grinder. Sampleshould be sufficiently ground in a few seconds. The grinder should not beallowed to operate more than 20 to 30 s as in such cases undesirablesample heating can occur.11. Proc
30、edureNOTE 6Refer to the general operating manual for gas chromatograph,the head-space sampler, and the series integrator for instructions inperforming steps in this procedure.11.1 Adjust the gas chromatograph to the conditions speci-fied in Appendix X1. Adjust the head-space sampler to theconditions
31、 in Appendix X2. Set the series integrator to theconditions in Appendix X3.11.2 Sample Analysis:11.2.1 Place 2 to 3 of polymer pellets (or crushed preform)into a small Dewar flask.11.2.2 Cover the polymer with 20 to 40 mL of liquidnitrogen.11.2.3 Allow the polymer to chill under the liquid nitrogenf
32、or approximately 3 min (or until most of the liquid N2 hasevaporated).11.2.4 Turn on the Wiley mill equipped with a 800 to1000-m screen.F201305211.2.5 Slowly pour the remaining liquid nitrogen from theDewar flask through the Wiley mill, followed by the chilledpolymer sample (tapping the sample may b
33、e required).11.2.6 Collect the ground polymer in a small glass jar orsmall manila envelope.11.2.7 Turn off the Wiley mill and clean it with a vacuumcleaner.11.2.8 Allow the ground polymer sample to come to roomtemperature (approximately 10 min).11.2.9 Weigh approximately 0.2000 (6 0.0200) g, recorde
34、dto the nearest 0.0001 g, into a 20-mL head-space vial.11.2.10 Place a septum (with TFE-fluorocarbon side downtowards the inside of the vial) on the vial. Place an aluminumcap on top of the septum, and crimp the cap with a crimperUNTIL THE CAP CANNOT BE TURNED. Remove thecenter piece of the aluminum
35、 cap (if it exists).11.2.11 Place the vial in the appropriate position in thehead-space sampler.11.2.12 Press the “Vial Parameter” key on the H-P 7964head-space sampler, and enter the starting and stopping vialpositions.11.2.13 Press the “START” button on the H-P 7694 head-space sampler.11.2.14 The
36、head-space sampler will heat the sample for 60min at 150C and then automatically inject the head-space gasand start the gas chromatograph and integrator.11.2.15 The final report will appear on the H-P 6890integrator or the data system when the GC is finished. Thisreport will give the micrograms of A
37、A.11.2.16 To determine the concentration in ppm of AA in thepolymer sample, divide the micrograms of AA (reported in11.2.15) by the sample weight in the vial (recorded in 11.2.9 asgrams of polymer).12. Calculation12.1 The AA response factor is calculated as described in9.11 and 9.12. The ppm of AA c
38、an be calculated manually bymultiplying the response factor and the area of the AA peak,and then dividing this number by the sample weight in the vial(in grams).13. Report13.1 Report the ppm of AA to two decimal places.14. Precision and Bias14.1 The following was taken from work completed by theInte
39、rnational Society of Beverage Technologists (ISBT) sub-committee concerning standardization of method to determineresidual AA in PET.14.2 The number of laboratories, materials, and determina-tions in this study meets the minimum requirements fordetermining precision in accordance with Practice E 691
40、.Acomplete report is on file at ASTM Headquarters.414.3 This round robin was conducted by having one labo-ratory mold PET preforms on a 48-cavity injection moldingmachine and selecting 6 of those cavities as the sample set.Even though these preforms all came from one PET sample(material), each cavit
41、y has its own unique AA value, and thus,were treated as six different materials.Also, two different typesof precision and bias were calculated, one based on eachlaboratory using their own calibration standard solution andanother when each laboratory calibrated with a “common”calibration standard.Pra
42、ctice E 691 Study MinimumLaboratories: 6 6Materials: 6 4Determinations: 3 214.4 Precision and Bias With Each Laboratory Using TheirOwn Calibration StandardPrecision, characterized by re-peatability, Sr and r, and reproducibility, SR and R, has beendetermined for the materials to be as follows:Materi
43、als Average Sr SR r RMaterial A 5.21 0.1812 0.6403 0.5074 1.7928Material B 6.25 0.4060 0.7464 1.1368 2.0899Material C 6.37 0.2880 0.6713 0.8066 1.8796Material D 7.21 0.3285 0.7743 0.9198 2.1680Material E 7.01 0.4217 0.8350 1.1808 2.3380Material F 5.88 0.3930 0.7168 1.1003 2.007114.4.1 Since the mate
44、rials used in this study are all from onespecific type of material (PET), but have different AA levelsbecause they are from different cavities, it makes more sense tohave one set of precision values rather than one for each cavity.This will be derived by squaring each Sr and SR, averagingeach of Sr2
45、and SR2across materials and taking the square root.Sr SR r R0.3466 0.7335 0.9705 2.053814.4.1.1 Standard Deviation (Sr)Sr is the square root ofthe average within laboratory variance.14.4.1.2 Standard Deviation (SR)SR is the square root ofthe sum of the within laboratory variance and between labo-rat
46、ory variance of the laboratory means.14.4.1.3 Repeatabilityr is the interval representing thelargest expected difference between two test results for thesame material, obtained by the same operator using the sameequipment on the same day in the same laboratory.Adifferencelarger than r indicates more
47、 variation is present than expected.14.4.1.4 ReproducibilityR is the interval representing thelargest expected difference between two test results for thesame material, obtained by different operators using differentequipment in different laboratories, not necessarily on the sameday. A difference la
48、rger than R indicates more variation ispresent than expected.14.5 Precision and Bias When Each Laboratory Uses aCommon Calibration StandardPrecision, characterized byrepeatability, Sr and r, and reproducibility, SR and R, has beendetermined for the materials to be as follows:4Supporting data have be
49、en filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:F021015.F2013053Materials Average Sr SR r RMaterial A 5.42 0.1849 0.4128 0.5178 1.1596Material B 6.47 0.4123 0.6438 1.1545 1.8026Material C 6.59 0.2703 0.5020 0.7567 1.4057Material D 7.45 0.3113 0.6333 0.8716 1.7732Material E 7.26 0.4014 0.5747 1.1240 1.6090Material F 6.10 0.3854 0.5085 1.0792 1.423714.5.1 Since the materials used in this study are all from onespecific type of material (PET), but have different AA levelsbecause they are from different cavities,
