1、Designation: D7882 13Standard Test Method forDetermination of 4-Carboxybenzaldehyde and p-Toluic Acidin Purified Terephthalic Acid by Capillary Electrophoresiswith Normal Voltage Mode1This standard is issued under the fixed designation D7882; the number immediately following the designation indicate
2、s 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of4-
3、carboxybenzaldehyde (4-CBA) and p-toluic acid (p-TOL) inpurified terephthalic acid (PTA) by capillary electrophoresis(CE) with normal voltage mode and UV detection. It isapplicable for 4-CBAfrom 5 to 400 mg/kg and for p-TOLfrom10 to 400 mg/kg, respectively.1.2 In determining the conformance of the t
4、est results usingthis method to applicable specifications, results shall berounded off in accordance with the rounding-off method ofPractice E29.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purp
5、ort 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.2. Referenced Documents2.1 ASTM Standards:2D11
6、93 Specification for Reagent WaterD4790 Terminology of Aromatic Hydrocarbons and RelatedChemicalsD6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and Related Ma-terialsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with Specifi
7、cationsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ISO Document:3EN ISO 8213 Chemical Products for Industrial UseSampling TechniquesSolid Chemical Products in theForm of P
8、articles Varying from Powders to Coarse Lumps2.3 Other Document:4OSHA Regulations 29 CFR paragraphs 1910.1000 and1910.12003. Terminology3.1 Definitions of Terms Specific to Normal Voltage Mode inthis Standard:3.1.1 capillary electrophoresis, nan electrophoretic tech-nique in which a sample is introd
9、uced into a 50 to 100 m i.d.fused-silica capillary filled with electrolyte solution and sub-jected to high voltage for separation.3.1.1.1 DiscussionNormal voltage, with the anode on theinjection side and the cathode on the detection side, is appliedacross the capillary causing electrolyte and analyt
10、es to migratetowards the cathode and through the capillarys UV detectorwindow. Analytes are separated based on the differential ratesof migration in the electric field. Analyte detection andquantitation are based on the principles of UV detection.3.1.2 electrolye, na combination of a buffer reagent
11、and anion-pair reagent dissolved in an aqueous solution and placedinside the capillary, used as a carrier for the analytes.3.1.3 electroosmotic flow (EOF), nthe directional velocityof electrolyte-solution flow within the capillary under anapplied voltage; the velocity and direction of flow are deter
12、-mined by electrolyte chemistry, capillary-wall chemistry, andapplied voltage (see Fig. 1).1This test method is under the jurisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.02 on Oxygenated Aromatics.Current edition ap
13、proved Aug. 15, 2013. Published October 2013. DOI:10.1520/D7882-13.2For 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 we
14、bsite.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from U.S. Government Printing Office Superintendent of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http:/www.access.gpo.gov.Copy
15、right ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.4 electropherogram, na graphical presentation of UVdetector response versus time of analysis; the x-axis is migra-tion time, which is used to identify the analyte qualitatively,and the y
16、-axis is UV response, which can be converted to peakarea or height for quantitation.3.1.5 electrophoretic mobility, nthe specific velocity of acharged analyte in the electrolyte under specificelectroosmotic-flow conditions.3.1.5.1 DiscussionThe mobility of an analyte is directlyrelated to the analyt
17、es equivalent ionic conductance andapplies voltage, and is the primary mechanism of separation.3.1.6 hydrodynamic sampling, na sample introductiontechnique in which the injection side of the capillary withelectrolyte is immersed into sample solution and then a positivepressure difference is applied.
18、3.1.6.1 DiscussionNanolitres of sample are introducedinto the capillary without analyte bias effects.3.1.7 migration time, nthe time required for a specificanalyte to migrate through the capillary to the detector.3.1.7.1 DiscussionThe migration time in capillary electro-phoresis is analogous to rete
19、ntion time in chromatography.4. Summary of Test Method4.1 A PTA sample is dissolved in ammonium hydroxidesolution. The 4-CBA, p-TOL and PTA dissociate and becomehomologous ions under basic conditions. A fixed amount ofthis solution is introduced into the capillary using hydrody-namic sampling. A vol
20、tage is applied to the capillary toseparate the impurities, 4-CBA, and p-TOL, from PTA. Exter-nal standard calibration is used for quantification.5. Significance and Use5.1 The presence of 4-CBA and p-TOL in PTA used for theproduction of polyester is undesirable because they can slowdown the polymer
21、ization process; and 4-CBAis also impartingcoloration to the polymer due to thermal instability.5.2 Determining the amount of 4-CBA and p-TOL remain-ing from the manufacture of PTA is often required. This testmethod is suitable for setting specifications and for use as aninternal quality control whe
22、re these products are produced orused.5.3 This test method is intended as an alternative to theHPLC method for determination of 4-CBA and p-TOL in PTA.The major benefits of CE are speed, simplicity, reduced reagentconsumption and operating costs.6. Apparatus6.1 Capillary Electrophoresis Systemthe sy
23、stem consistsof the following components, as shown in Fig. 2 or equivalent:6.1.1 High Voltage Power Supply, capable of generatingvoltage between 0 and 30 kV with the capability of working ina constant voltage mode.6.1.2 Covered Sample Carousel, to prevent environmentalcontamination of the samples an
24、d electrolytes during a multi-sample batch analysis.FIG. 1 Pictorial Diagram of Charged and Neutral Species Mobilities in CEFIG. 2 Typical Instrumental SetupD7882 1326.1.3 Sample Introduction Mechanism, capable of hydrody-namic sampling technique.6.1.4 Capillary Purge Mechanism, to purge the capilla
25、ryafter every analysis with fresh electrolyte to eliminate anyinterference from the previous sample matrix, and to clean thecapillary with sodium hydroxide solution and water.6.1.5 UV Detector, having the capability of monitoring 200nm, or equivalent.6.1.6 Fused Silica Capillary, a 50 to 100 m (inne
26、r diam-eter) by 375 m (outer diameter) by 60 cm (length) having apolymer coating for flexibility, with an uncoated section to actas the cell window for UV detection.6.1.7 Constant Temperature Compartment, to keep thesamples, capillary, and electrolytes at constant temperature.6.2 Data System, a comp
27、uter system that can acquire data at20 points/s minimum, express migration time in minutes tothree decimal places.6.3 Sample Filter, a disposable syringe filter made ofcellulose acetate, with a pore size between 0.22 and 0.45 m,and is chemically inert to aqueous solutions, is recommendedfor the remo
28、val of particulate matter from the sample solution.6.4 pH Meter, consisting of a glass-calomel doubleelectrode, used to determine pH values of the solutions.7. Reagents and Materials7.1 Purity of ReagentsUnless otherwise indicated, it isintended that all reagents shall conform to the reagent gradesp
29、ecification for analytical reagents of the American ChemicalSociety, where such specifications are available.5Other gradesmay be used, provided it is first ascertained that the reagent isof sufficiently high purity to permit its use without lesseningthe performance or accuracy of the determination.
30、Reagentchemicals shall be used for all tests.NOTE 1Calibration and detection limits of this test method can bebiased by the purity of the reagents.7.2 Sodium 1-heptanesulfonate.7.3 Sodium Phosphate Tribasic Dodecahydrate.7.4 Sodium Hydroxide.7.5 25 % (w/w) Ammonium Hydroxide Solution.7.6 Purity of W
31、aterUnless otherwise indicated, referencesto water shall be understood to mean Type 1 reagent waterconforming to or exceeding Specification D1193. Freshlydrawn water should be used for preparation of all stock andworking standards, electrolytes, and solutions.7.7 PTA Standard for CalibrationA certif
32、ied PTA calibra-tion standard with known amounts of 4-CBA and p-TOL isrequired. If it is not commercially available, please refer toAnnex A1 for determining the concentrations of 4-CBA andp-TOL in a PTA sample. The calibrated PTA sample can beserved as a PTA calibration standard.7.8 Sodium Hydroxide
33、 Solution (0.5 mol/L sodiumhydroxide)Dissolve approximately 20 g of sodium hydroxideina1Lplastic volumetric flask and dilute to 1 L with water.7.9 Ammonium Hydroxide Solution (2.5 % (m/m) ammo-nium hydroxide solution)Add approximately 50 mL 25 %(m/m) ammonium hydroxide solution in a 500-mL volumetri
34、cflask and dilute to 500 mL with water.7.10 Electrolyte Solution, Working in Normal Voltage Mode(50 mM sodium 1-heptanesulfonate and 10 mM trisodiumphosphate)Dissolve approximately 0.50 g sodium1-heptanesulfonate and 0.19 g sodium phosphate tribasicdodecahydrate in a 50-mL volumetric flask and dilut
35、e to 50 mLwith water. Filter and degas the solution before use.8. Hazards8.1 Consult current federal regulations, suppliers MaterialSafety Data Sheets, and local regulations for all materials usedin this test method.9. Sampling9.1 Use only representative samples obtained as describedin EN ISO 8213,
36、unless otherwise specified.10. Preparation of Apparatus10.1 Set up the CE and data system according to themanufacturers instructions and adjust the instrument to theconditions described in Table 1 with the following procedures.10.2 Program the CE system to maintain a constant tem-perature. Fill the
37、electrolyte reservoirs with fresh electrolyteworking solution, and allow 10 min for thermal equilibration.10.3 Condition a new capillary with 0.5 mol/L sodiumhydroxide solution for 5 min followed by water for 5 min.Purge the capillary with electrolyte for 3 min.10.4 Apply 15 kV voltage and test for
38、current. If no currentis observed, then there is a bubble, or blockage, or both, in thecapillary. Degas the electrolyte working solution and retry. Ifstill no current, replace the capillary.10.5 Set the UV detector to 200 nm detection, or equivalent.Zero the detector to 0.000 absorbance. UV offset i
39、s less than0.1 AU.10.6 Program the CE system with the constant voltage of+(15-25) kV for normal voltage mode.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society,
40、see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.TABLE 1 Recommended Operating ConditionsNormal Voltage ModeElectrolyte 50 mM sodium 1-heptanesulfonate and 1
41、0 mMtrisodium phosphateApplied voltage +(15-25) kVInjection technique Hydrodynamic sampling3.3 kPa*15 sCapillary purge program water 10 min; Electrolyte 6 minCapillary Inner diameter (50-100) m; length (40-70) cmDetector UV; 200 nm or equivalentCapillary temperature (20-30) CD7882 13310.7 Program th
42、e CE system for a hydrodynamic sampling.Different sampling times may be used provided that thesamples and standards are analyzed identically.10.8 Program the CE system for 10 min and 6 min, purgewith water and the electrolyte in series between each analysis.10.9 Program the data system for an acquis
43、ition rate of atleast 20 points/s. Program the data system to identify analytepeaks based on migration time, and to quantitate analyte peakresponse using peak area.11. Procedure11.1 Calibration:11.1.1 Accurately weigh, to the nearest 0.0001 g, about 0.5g of PTA standard in a 25 mL beaker, add 7 mL o
44、f ammoniumhydroxide solution (see 7.9), stir with heat or use an ultrasonicbath until PTA is completely dissolved. Then accuratelytransfer the resulting solution to a 25 mL volumetric flask anddilute with water to the mark. When the operating conditionsare steady, inject an amount of the calibration
45、 standard solutioninto the CE for analysis. Record electropherograms and thepeak area values for 4-CBAand p-TOL, respectively, using thedata system. Analyze the calibration standard a minimum ofthree times and calculate the average peak area.11.2 Analysis of Samples:11.2.1 Accurately weigh, to the n
46、earest 0.0001 g, about 0.5g PTA sample, repeat the remaining steps in 11.1, and recordpeak area values of 4-CBA adn p-TOL, respectively. Run thesample. After each analysis, rinse the capillary with water for10 min, and then with electrolyte for 6 min. Representativeelectropherogram of a PTA sample i
47、s shown in Fig. 3.12. Calculation12.1 Calculate the concentration of 4-CBA or p-TOL inmg/kg using the following equation:X 5ms A Csm As(1)where:X = concentraton of 4-CBA or p-TOL in the PTA sample,mg/kg,A = peak area of 4-CBA or p-TOL in the PTA sample,m = weight of the PTA sample, g,As= average pea
48、k area of 4-CBA or p-TOL in the PTAstandard,Cs= concentration of 4-CBA or p-TOL in the PTA standard,mg/kg,ms= weight of the PTA standard, g.13. Report13.1 Report the concentration of 4-CBA and p-TOL in thePTA sample to the nearest 1 mg/kg.13.2 Report the following information in the report:13.2.1 Th
49、e complete identification of the sample tested.13.2.2 Any deviation from the procedure specified (forexample, detailed description of column and operating condi-tions).13.2.3 Results of the test.13.2.4 Any abnormal situations observed during the test.14. Precision and Bias614.1 The precision of this test method is based on anintralaboratory study of Test Method D7882 conducted in2012. One laboratory tested one PTA sample and one qualifiedterephthalic acid (QTA) sample for 4-CBA and p-TOL. Everytest result represents an individual determination. T
