1、Designation: D7881 13Standard Test Method forDetermination of 4-Carboxybenzaldehyde and p-Toluic Acidin Purified Terephthalic Acid by Capillary Electrophoresiswith Reverse Voltage Mode1This standard is issued under the fixed designation D7881; the number immediately following the designation indicat
2、es 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 method2covers the determination of4
3、-carboxybenzaldehyde (4-CBA) and p-toluic acid (p-TOL) inpurified terephthalic acid (PTA) by capillary electrophoresis(CE) with reverse voltage mode and UV detection. It isapplicable for 4-CBAfrom 3 to 400 mg/kg and for p-TOLfrom8 to 400 mg/kg, respectively.1.2 In determining the conformance of the
4、test results usingthis method to applicable specification, results shall be roundedoff in accordance with the rounding-off method of PracticeE29.1.3 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:3D11
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 Documents:4EN ISO 8213 Chemical Products for Industrial UseSampling TechniquesSolid Chemical Products in theForm of
8、Particles Varying from Powders to Coarse Lumps2.3 Other Document:5OSHA Regulations, 29 CFR paragraphs 1910.1000 and1910.12003. Terminology3.1 Definitions of Terms Specific to Reverse Voltage Mode inthis Standard:3.1.1 capillary electrophoresis, nan electrophoretic tech-nique in which a sample is int
9、roduced into a 50 m to 100 mi. d. fused-silica capillary filled with electrolyte solution andsubjected to high voltage for separation.3.1.1.1 DiscussionReverse voltage, with the cathode onthe injection side and the anode on the detection side, is appliedacross the capillary causing electrolyte and a
10、nalytes to migratetowards the anode and through the capillarys UV detectorwindow. Analytes are separated based upon the differentialrates of migration in the electrical field. Analyte detection andquantitation are based upon the principles of UV detection.3.1.2 electrolyte, na combination of a buffe
11、r reagent, anion-pair reagent and an electroosmotic-flow modifier placedinside the capillary, used as a carrier for the analytes, and fordetection and quantitation.1This test method is under the jurisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct respon
12、sibility ofSubcommittee D16.02 on Oxygenated Aromatics.Current edition approved Aug. 15, 2013. Published October 2013. DOI:10.1520/D7881-13.2This standard is based on SH/T 16872000 Purified terephthalic acid forindustrial usedetermination of 4-Carboxybenzaldehyde and p-Toluic Acid-Highperformance ca
13、pillary electrophoresis (HPCE), copyright SINOPEC, 22 Chaoyang-men North Street, Chaoyang District, Beijing, China 100728. A copy of SH/T16872000 may be obtained from China Petrochemical Press, www.sinopec-.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
14、 Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from Available from American National Standards Institute (ANSI),25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.5Available f
15、rom U.S. Government Printing Office Superintendent of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http:/www.access.gpo.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.3 electroosmotic flow (EOF), nt
16、he directional velocityof electrolyte-solution flow within the capillary under anapplied voltage; the velocity and direction of flow are deter-mined by electrolyte chemistry, capillary-wall chemistry, andapplied voltage.3.1.4 electroosmotic-flow modifier (OFM), na cationicquaternary amine in the ele
17、ctrolyte that dynamically coats thenegatively charged silica wall giving it a net positive charge.3.1.4.1 DiscussionThis modifier reverses the direction ofthe electrolytes natural electroosmotic flow and directs ittowards the anode and detector. This modifier augments theanalytes migration and enhan
18、ces speed of analysis (see Fig. 1).3.1.5 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-axis is UV response, which can be converted to peakarea or height for quan
19、titation.3.1.6 electrophoretic mobility, nthe specific velocity of acharged analyte in the electrolyte under specificelectroosmotic-flow conditions.3.1.6.1 DiscussionThe mobility of an analyte is directlyrelated to the analytes equivalent ionic conductance andapplied voltage, and is the primary mech
20、anism of separation.3.1.7 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.3.1.7.1 DiscussionNanolitres of sample are introducedinto the capillary wit
21、hout analyte bias effects.3.1.8 electrokinetic sampling, na sample introductiontechnique in which the injection side of the capillary withelectrolyte and the electrode are inserted into the samplesolution.Avoltage is then applied, causing analytes to enter thecapillary by electrophoretic migration a
22、nd EOF.3.1.8.1 DiscussionNanolitres of sample are injected intothe capillary with analyte bias effects. It has considerablebenefit in terms of increased sensitivity when attempting toquantify trace levels of analytes.3.1.9 migration time, nthe time required for a specificanalyte to migrate through t
23、he capillary to the detector.3.1.9.1 DiscussionThe migration time in capillary electro-phoresis is analogous to retention 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 b
24、asic conditions. A fixed amount ofthis solution is introduced into the capillary using hydrody-namic sampling or electrokinetic sampling. A voltage is ap-plied to the capillary to separate the impurities, 4-CBA andp-TOL, from PTA. External standard calibration is used forquantification.5. Significan
25、ce 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 polymerization 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 t
26、he manufacture of PTA is often required. This testmethod is suitable for setting specifications and for use as aninternal quality control where these products are produced orused.5.3 This test method is intended as an alternative to theHPLC method for the determination of 4-CBA and p-TOL inPTA. The
27、major benefits of CE are speed, simplicity, reducedreagent consumption, and operating costs.FIG. 1 Pictorial Diagram of Anion Mobility and Electroosmotic Flow ModifierD7881 1326. Apparatus6.1 Capillary Electrophoresis SystemThe system consistsof the following components, as shown in Fig. 2, or equiv
28、alent: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 and electrolytes during a multi-sample batch analysis.6.1.3 Sample Intr
29、oduction Mechanism, capable of hydrody-namic sampling or electrokinetic sampling technique.6.1.4 Capillary Purge Mechanism, to purge the capillaryafter every analysis with fresh electrolyte to eliminate anyinterference from the previous sample matrix, and to clean thecapillary with sodium hydroxide
30、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 (inner 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 d
31、etection.6.1.7 Constant Temperature Compartment, to keep thesamples, capillary, and electrolytes at constant temperature.6.2 Data System, a computer system that can acquire data at20 points/s minimum, express migration time in minutes tothree decimal places.6.3 Sample Filter, a disposable syringe fi
32、lter made ofcellulose acetate, with a pore size between 0.22 and 0.45 m,and is chemically inert to aqueous solutions, is recommendedfor the removal 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
33、.7. Reagents and Materials7.1 Purity of ReagentsUnless otherwise indicated, it isintended that all reagents shall conform to the reagent gradespecification for analytical reagents of the American ChemicalSociety, where such specifications are available.6Other gradesmay be used, provided it is first
34、ascertained that the reagent isof sufficiently high purity to permit its use without lesseningthe performance or accuracy the determination. 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 Tetradec
35、yltrimethylAmmonium Chloride.7.3 Sodium 1-hexanesulfonate.7.4 3-(Cyclohexylamino)-1-propanesulfonic Acid.7.5 Sodium Phosphate Dibasic Dodecahydrate.7.6 Sodium Hydroxide.7.7 25 % (w/w) Ammonium Hydroxide Solution.7.8 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to
36、 mean Type 1 reagent waterconforming or exceeding Specification D1193. Freshly drawnwater should be used for preparation of all stock and workingstandards, electrolytes, and solutions.7.9 PTA Standard for CalibrationsA certified PTA cali-bration standard with known amounts of 4-CBA and p-TOL isrequi
37、red. 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.7.10 OFM Concentrate Solution (0.05 mol/L tetradecyltrim-ethyl ammonium chloride)Dissolve appro
38、ximately 0.75 g oftetradecyltrimethyl ammonium chloride (TTAC) in a 50-mLvolumetric flask and dilute to 50 mL with water.7.11 Sodium Hydroxide Solution (0.5 mol/L sodiumhydroxide)Dissolve approximately 20 g of sodium hydroxideina1Lplastic volumetric flask and dilute to 1 L with water.7.12 Ammonium H
39、ydroxide Solution (2.5 % (m/m) ammo-nium hydroxide solution)Add approximately 50 mL 25 %(m/m) ammonium hydroxide solution in a 500-mL volumetricflask and dilute to 500 mL with water.7.13 Electrolyte Solution, working in reverse voltage mode.7.13.1 Electrolyte solution A (50 mm sodium1-hexanesulfonat
40、e, 10 mM disodium hydrogen phosphate and1mM OFM)Weigh approximately 0.50 g sodium1-hexanesulfonate and 0.18 g sodium phosphate dibasic do-decahydrate in a 50-mL volumetric flask, add 1 mL OFMconcentrate solution and dilute to 50 mL with water.Adjust thesolution pH to 10.5 to 11.0 using 7.11 sodium h
41、ydroxidesolution. Filter and degas the solution before use.7.13.2 Electrolyte Solution B (50 mM sodium1-hexanesulfonate, 5 mM CAPS and 1 mM OFM)Weighapproximately 0.50 g sodium 1-hexanesulfonate and 0.06 g6Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washing
42、ton, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, 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.FIG. 2 Typic
43、al Instrumental SetupD7881 1333-(cyclohexylamino)-1-propanesulfonic acid (CAPS) in a50-mL volumetric flask, add 1 mL OFM concentrate solutionand dilute to 50 mL with water. Adjust the solution pH to 10.5to 11.0 using 7.11 sodium hydroxide solution. Filter and degasthe solution before use.8. Hazards8
44、.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, unless otherwise specified.10. Preparation of Apparatus10.1 Set up the CE
45、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 electrolyte reservoirs with fresh electrolyteworking solution and allow 10
46、 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 current. If no currentis observed, then there is a bubble or blockage, or b
47、oth, 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 is less than0.1 AU.10.6 Program the CE system with constant voltage of-(15-25
48、) kV for reverse voltage mode.10.7 Program the CE system for a hydrodynamic samplingor electrokinetic sampling. Different sampling times may beused provided that the samples and standards are analyzedidentically.10.8 Program the CE system for 1 min, 2 min, and 3 min,and purge with sodium hydroxide s
49、olution, water and theelectrolyte in series between each analysis.10.9 Program the data system for an acquisition 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 of ammoniumhydroxide solution (see 7.12), stir with heat or use an ultrasonicbath until PTA is completely dissolved. Then accurate
