ASTM D7882-20

Standard Test Method for Determination of 4-Carboxybenzaldehyde and <emph type="bdit" >p</emph>-Toluic Acid in Purified Terephthalic Acid by Capillary Electrophoresis with Normal Voltage Mode

SIGNIFICANCE AND USE
5.1 The presence of 4-CBA and p-TOL in PTA used for the production of polyester is undesirable because they can slow down the polymerization process; and 4-CBA is also imparting coloration to the polymer due to thermal instability.  
5.2 Determining the amount of 4-CBA and p-TOL remaining from the manufacture of PTA is often required. This test method is suitable for setting specifications and for use as an internal quality control where these products are produced or used.  
5.3 This test method is intended as an alternative to the HPLC method for determination of 4-CBA and p-TOL in PTA. The major benefits of CE are speed, simplicity, reduced reagent consumption and operating costs.
SCOPE
1.1 This test method covers the determination of 4-carboxybenzaldehyde (4-CBA) and p-toluic acid (p-TOL) in purified terephthalic acid (PTA) by capillary electrophoresis (CE) with normal voltage mode and UV detection. It is applicable for 4-CBA from 5 to 400 mg/kg and for p-TOL from 10 to 400 mg/kg, respectively.  
1.2 In determining the conformance of the test results using this method to applicable specifications, results shall be rounded off in accordance with the rounding-off method of Practice E29.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 71.080.40 - Organic acids
• Technical Committee: D16 - Aromatic, Industrial, Specialty and Related Chemicals
• Drafting Committee: D16.02 - Oxygenated Aromatics

Relations

• Refers: ASTM D6809-02(2016) - Standard Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
• Effective Date: 01-Nov-2016
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM E29-08 - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 01-Oct-2008
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM D6809-02(2007) - Standard Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
• Effective Date: 01-Jun-2007
• Refers: ASTM E29-06b - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 15-Nov-2006
• Refers: ASTM E29-06a - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 15-Sep-2006
• Refers: ASTM E29-06 - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 01-May-2006
• Refers: ASTM D1193-06 - Standard Specification for Reagent Water
• Effective Date: 01-Mar-2006
• Refers: ASTM E691-05 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2005
• Refers: ASTM E29-04 - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 01-Dec-2004
• Refers: ASTM D6809-02 - Standard Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
• Effective Date: 10-Jun-2002
• Refers: ASTM E29-02e1 - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 10-May-2002
• Refers: ASTM E691-99 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 10-May-1999

Overview

ASTM D7882-20 is the standard test method for determining 4-carboxybenzaldehyde (4-CBA) and p-toluic acid (p-TOL) in purified terephthalic acid (PTA) using capillary electrophoresis (CE) in normal voltage mode with UV detection. This analytical method is essential for the polyester industry, where the presence of 4-CBA and p-TOL in PTA is undesirable, as these impurities can slow down polymerization and, in the case of 4-CBA, cause coloration in the final product. ASTM D7882-20 provides an alternative to the traditional HPLC method, offering benefits in terms of speed, simplicity, and reduced reagent consumption.

Key Topics

• Substances Detected: 4-carboxybenzaldehyde (4-CBA) and p-toluic acid (p-TOL) are impurities that must be strictly controlled in PTA used for polyester production.
• Test Method: The standard specifies capillary electrophoresis with normal voltage mode and UV detection, covering:
  • 4-CBA determination in the range of 5 to 400 mg/kg
  • p-TOL determination in the range of 10 to 400 mg/kg
• Sample Preparation: Dissolving PTA samples in ammonium hydroxide, hydrodynamic injection into the capillary, and separation by applying voltage.
• Significance: Monitoring impurities in PTA helps maintain product quality, assure compliance with industry specifications, and supports internal quality control programs.
• Benefits of CE Method:
  • Faster analysis times compared to HPLC
  • Lower reagent and operating costs
  • Enhanced simplicity and reduced environmental impact

Applications

ASTM D7882-20 is most relevant in industries involved in the production, quality control, and use of purified terephthalic acid, with practical applications including:

• Polyester Manufacturing: Ensuring raw material (PTA) quality for polymerization processes, preventing unwanted delays and color issues in polyester fibers, resins, and films.
• Internal Quality Control: Regular in-process and finished product testing in PTA production facilities.
• Specification Setting and Compliance: Validating that PTA supplied or purchased meets international standards and customer requirements on impurity levels.
• Analytical Testing Laboratories: Providing an efficient, cost-effective alternative to HPLC for high-throughput testing scenarios.

Related Standards

Several ASTM and international standards complement or support the implementation of ASTM D7882-20:

• ASTM D1193: Specification for reagent water, relevant for preparing solutions and calibration standards.
• ASTM D6809: Guide for quality control procedures for aromatic hydrocarbons and related materials.
• ASTM E29: Practice for using significant digits when reporting test data to ensure consistency with specifications.
• ASTM E691: Practice for conducting interlaboratory studies to determine test method precision.
• EN ISO 8213: ISO standard for sampling techniques of chemical products in particulate form.
• OSHA 29 CFR 1910.1000 and 1910.1200: U.S. regulations on safety and handling of chemicals.

Practical Value

ASTM D7882-20 delivers significant value by enabling consistent and rapid testing of PTA quality through robust capillary electrophoresis. This ensures production efficiency, cost savings, and regulatory compliance for polyester manufacturers and chemical producers globally. The method’s adaptability, speed, and lower resource consumption position it as a preferred technique for routine quality assurance of PTA. Employing this standard helps organizations achieve higher confidence in product purity, supporting both in-house quality protocols and external supply chain requirements.

Keywords: ASTM D7882-20, capillary electrophoresis, purified terephthalic acid, 4-carboxybenzaldehyde, p-toluic acid, PTA analysis, polyester production, quality control, impurity determination, standard test method.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:D7882 −20
Standard Test Method for
Determination of 4-Carboxybenzaldehyde and p-Toluic Acid
in Purified Terephthalic Acid by Capillary Electrophoresis
with Normal Voltage Mode
This standard is issued under the fixed designation D7882; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* Procedures for Aromatic Hydrocarbons and Related Ma-
terials
1.1 This test method covers the determination of
E29 Practice for Using Significant Digits in Test Data to
4-carboxybenzaldehyde (4-CBA) and p-toluic acid (p-TOL) in
Determine Conformance with Specifications
purified terephthalic acid (PTA) by capillary electrophoresis
E691 Practice for Conducting an Interlaboratory Study to
(CE) with normal voltage mode and UV detection. It is
Determine the Precision of a Test Method
applicablefor4-CBAfrom5to400mg/kgandforp-TOLfrom
2.2 ISO Document:
10 to 400 mg/kg, respectively.
EN ISO 8213 Chemical Products for Industrial Use—
1.2 In determining the conformance of the test results using
Sampling Techniques—Solid Chemical Products in the
this method to applicable specifications, results shall be
Form of ParticlesVarying from Powders to Coarse Lumps
rounded off in accordance with the rounding-off method of
2.3 Other Document:
Practice E29.
OSHA Regulations 29 CFR paragraphs 1910.1000 and
1.3 The values stated in SI units are to be regarded as 1910.1200
standard. No other units of measurement are included in this
3. Terminology
standard.
3.1 Definitions of Terms Specific to Normal Voltage Mode in
1.4 This standard does not purport to address all of the
this Standard:
safety concerns, if any, associated with its use. It is the
3.1.1 capillary electrophoresis, n—an electrophoretic tech-
responsibility of the user of this standard to establish appro-
nique in which a sample is introduced into a 50 to 100 µm i.d.
priate safety, health, and environmental practices and deter-
fused-silica capillary filled with electrolyte solution and sub-
mine the applicability of regulatory limitations prior to use.
jected to high voltage for separation.
1.5 This international standard was developed in accor-
3.1.1.1 Discussion—Normal voltage, with the anode on the
dance with internationally recognized principles on standard-
injection side and the cathode on the detection side, is applied
ization established in the Decision on Principles for the
across the capillary causing electrolyte and analytes to migrate
Development of International Standards, Guides and Recom-
towards the cathode and through the capillary’s UV detector
mendations issued by the World Trade Organization Technical
window. Analytes are separated based on the differential rates
Barriers to Trade (TBT) Committee.
of migration in the electric field. Analyte detection and
quantitation are based on the principles of UV detection.
2. Referenced Documents
2 3.1.2 electrolye,n—acombinationofabufferreagentandan
2.1 ASTM Standards:
ion-pair reagent dissolved in an aqueous solution and placed
D1193 Specification for Reagent Water
inside the capillary, used as a carrier for the analytes.
D6809 Guide for Quality Control and Quality Assurance
3.1.3 electroosmotic flow (EOF), n—the directional velocity
of electrolyte-solution flow within the capillary under an
applied voltage; the velocity and direction of flow are deter-
This test method is under the jurisdiction of ASTM Committee D16 on
Aromatic, Industrial, Specialty and Related Chemicals and is the direct responsi-
mined by electrolyte chemistry, capillary-wall chemistry, and
bility of Subcommittee D16.02 on Oxygenated Aromatics.
applied voltage (see Fig. 1).
Current edition approved Oct. 1, 2020. Published December 2020. Originally
approved in 2013. Last previous edition approved in 2019 as D7882 – 19. DOI:
10.1520/D7882-20. Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 4th Floor, New York, NY 10036, http://www.ansi.org.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
Standards volume information, refer to the standard’s Document Summary page on 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
the ASTM website. www.access.gpo.gov.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7882−20
FIG. 1Pictorial Diagram of Charged and Neutral Species Mobilities in CE
3.1.4 electropherogram, n—a graphical presentation of UV method is suitable for setting specifications and for use as an
detector response versus time of analysis; the x-axis is migra- internal quality control where these products are produced or
tion time, which is used to identify the analyte qualitatively, used.
and the y-axis is UVresponse, which can be converted to peak
5.3 This test method is intended as an alternative to the
area or height for quantitation.
HPLC method for determination of 4-CBAand p-TOLin PTA.
3.1.5 electrophoretic mobility, n—the specific velocity of a
ThemajorbenefitsofCEarespeed,simplicity,reducedreagent
charged analyte in the electrolyte under specific
consumption and operating costs.
electroosmotic-flow conditions.
6. Apparatus
3.1.5.1 Discussion—The mobility of an analyte is directly
related to the analyte’s equivalent ionic conductance and
6.1 Capillary Electrophoresis System—The system consists
applies voltage, and is the primary mechanism of separation.
of the following components, as shown in Fig. 2 or equivalent:
3.1.6 hydrodynamic sampling, n—a sample introduction 6.1.1 High Voltage Power Supply, capable of generating
technique in which the injection side of the capillary with voltage between 0 and 30 kV with the capability of working in
electrolyteisimmersedintosamplesolutionandthenapositive a constant voltage mode.
pressure difference is applied. 6.1.2 Covered Sample Carousel, to prevent environmental
3.1.6.1 Discussion—Nanolitres of sample are introduced contamination of the samples and electrolytes during a multi-
into the capillary without analyte bias effects. sample batch analysis.
3.1.7 migration time, n—the time required for a specific
analyte to migrate through the capillary to the detector.
3.1.7.1 Discussion—Themigrationtimeincapillaryelectro-
phoresis is analogous to retention time in chromatography.
4. Summary of Test Method
4.1 A PTA sample is dissolved in ammonium hydroxide
solution. The 4-CBA, p-TOL and PTA dissociate and become
homologous ions under basic conditions. A fixed amount of
this solution is introduced into the capillary using hydrody-
namic sampling. A voltage is applied to the capillary to
separate the impurities, 4-CBA, and p-TOL, from PTA. Exter-
nal standard calibration is used for quantification.
5. Significance and Use
5.1 The presence of 4-CBAand p-TOL in PTAused for the
production of polyester is undesirable because they can slow
down the polymerization process; and 4-CBAis also imparting
coloration 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 test FIG. 2Typical Instrumental Setup
D7882−20
6.1.3 Sample Introduction Mechanism, capable of hydrody- p-TOL in a PTA sample. The calibrated PTA sample can be
namic sampling technique. served as a PTA calibration standard.
6.1.4 Capillary Purge Mechanism, to purge the capillary
7.8 Sodium Hydroxide Solution (0.5 mol/L sodium
after every analysis with fresh electrolyte to eliminate any
hydroxide)—Dissolveapproximately20gofsodiumhydroxide
interference from the previous sample matrix, and to clean the
ina1L plastic volumetric flask and dilute to 1 L with water.
capillary with sodium hydroxide solution and water.
7.9 Ammonium Hydroxide Solution (2.5 % (m/m) ammo-
6.1.5 UV Detector, having the capability of monitoring 200
nium hydroxide solution)—Add approximately 50 mL 25 %
nm, or equivalent.
(m/m) ammonium hydroxide solution in a 500-mL volumetric
6.1.6 Fused Silica Capillary, a 50 to 100 µm (inner diam-
flask and dilute to 500 mL with water.
eter) by 375 µm (outer diameter) by 60 cm (length) having a
polymer coating for flexibility, with an uncoated section to act
7.10 Electrolyte Solution, Working in Normal Voltage Mode
as the cell window for UV detection. (50 mM sodium 1-heptanesulfonate and 10 mM trisodium
6.1.7 Constant Temperature Compartment, to keep the
phosphate)—Dissolve approximately 0.50 g sodium
samples, capillary, and electrolytes at constant temperature. 1-heptanesulfonate and 0.19 g sodium phosphate tribasic
dodecahydrateina50-mLvolumetricflaskanddiluteto50mL
6.2 Data System, a computer system that can acquire data at
with water. Filter and degas the solution before use.
20 points/s minimum, express migration time in minutes to
three decimal places.
8. Hazards
6.3 Sample Filter, a disposable syringe filter made of
8.1 Consult current federal regulations, supplier’s Safety
cellulose acetate, with a pore size between 0.22 and 0.45 µm,
Data Sheets, and local regulations for all materials used in this
and is chemically inert to aqueous solutions, is recommended
test method.
for the removal of particulate matter from the sample solution.
6.4 pH Meter, consisting of a glass-calomel double 9. Sampling
electrode, used to determine pH values of the solutions.
9.1 Use only representative samples obtained as described
in EN ISO 8213, unless otherwise specified.
7. Reagents and Materials
10. Preparation of Apparatus
7.1 Purity of Reagents—Unless otherwise indicated, it is
intended that all reagents shall conform to the reagent grade
10.1 Set up the CE and data system according to the
specification for analytical reagents of theAmerican Chemical
manufacturer’s instructions and adjust the instrument to the
Society, where such specifications are available. Other grades
conditions described in Table 1 with the following procedures.
may be used, provided it is first ascertained that the reagent is
10.2 Program the CE system to maintain a constant tem-
of sufficiently high purity to permit its use without lessening
perature. Fill the electrolyte reservoirs with fresh electrolyte
the performance or accuracy of the determination. Reagent
working solution, and allow 10 min for thermal equilibration.
chemicals shall be used for all tests.
10.3 Condition a new capillary with 0.5 mol/L sodium
NOTE 1—Calibration and detection limits of this test method can be
hydroxide solution for 5 min followed by water for 5 min.
biased by the purity of the reagents.
Purge the capillary with electrolyte for 3 min.
7.2 Sodium 1-heptanesulfonate.
10.4 Apply 15 kV voltage and test for current. If no current
7.3 Sodium Phosphate Tribasic Dodecahydrate.
is observed, then there is a bubble, or blockage, or both, in the
capillary. Degas the electrolyte working solution and retry. If
7.4 Sodium Hydroxide.
still no current, replace the capillary.
7.5 25 % (w/w) Ammonium Hydroxide Solution.
10.5 SettheUVdetectorto200nmdetection,orequivalent.
7.6 Purity of Water—Unless otherwise indicated, references
Zero the detector to 0.000 absorbance. UV offset is less than
to water shall be understood to mean Type 1 reagent water
0.1 AU.
conforming to or exceeding Specification D1193. Freshly
drawn water should be used for preparation of all stock and 10.6 Program the CE system with the constant voltage of
+(15-25) kV for normal voltage mode.
working standards, electrolytes, and solut
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7882 − 19 D7882 − 20
Standard Test Method for
Determination of 4-Carboxybenzaldehyde and p-Toluic Acid
in Purified Terephthalic Acid by Capillary Electrophoresis
with Normal Voltage Mode
This standard is issued under the fixed designation D7882; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method covers the determination of 4-carboxybenzaldehyde (4-CBA) and p-toluic acid (p-TOL) in purified
terephthalic acid (PTA) by capillary electrophoresis (CE) with normal voltage mode and UV detection. It is applicable for 4-CBA
from 5 to 400 mg/kg and for p-TOL from 10 to 400 mg/kg, respectively.
1.2 In determining the conformance of the test results using this method to applicable specifications, results shall be rounded off
in accordance with the rounding-off method of Practice E29.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D6809 Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 ISO Document:
EN ISO 8213 Chemical Products for Industrial Use—Sampling Techniques—Solid Chemical Products in the Form of Particles
Varying from Powders to Coarse Lumps
This test method is under the jurisdiction of ASTM Committee D16 on Aromatic, Industrial, Specialty and Related Chemicals and is the direct responsibility of
Subcommittee D16.02 on Oxygenated Aromatics.
Current edition approved Nov. 1, 2019Oct. 1, 2020. Published December 2019December 2020. Originally approved in 2013. Last previous edition approved in 20132019
as D7882 – 13.D7882 – 19. DOI: 10.1520/D7882-19.10.1520/D7882-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7882 − 20
2.3 Other Document:
OSHA Regulations 29 CFR paragraphs 1910.1000 and 1910.1200
3. Terminology
3.1 Definitions of Terms Specific to Normal Voltage Mode in this Standard:
3.1.1 capillary electrophoresis, n—an electrophoretic technique in which a sample is introduced into a 50 to 100 μm i.d.
fused-silica capillary filled with electrolyte solution and subjected to high voltage for separation.
3.1.1.1 Discussion—
Normal voltage, with the anode on the injection side and the cathode on the detection side, is applied across the capillary causing
electrolyte and analytes to migrate towards the cathode and through the capillary’s UV detector window. Analytes are separated
based on the differential rates of migration in the electric field. Analyte detection and quantitation are based on the principles of
UV detection.
3.1.2 electrolye, n—a combination of a buffer reagent and an ion-pair reagent dissolved in an aqueous solution and placed inside
the capillary, used as a carrier for the analytes.
3.1.3 electroosmotic flow (EOF), n—the directional velocity of electrolyte-solution flow within the capillary under an applied
voltage; the velocity and direction of flow are determined by electrolyte chemistry, capillary-wall chemistry, and applied voltage
(see Fig. 1).
3.1.4 electropherogram, n—a graphical presentation of UV detector response versus time of analysis; the x-axis is migration time,
which is used to identify the analyte qualitatively, and the y-axis is UV response, which can be converted to peak area or height
for quantitation.
3.1.5 electrophoretic mobility, n—the specific velocity of a charged analyte in the electrolyte under specific electroosmotic-flow
conditions.
3.1.5.1 Discussion—
The mobility of an analyte is directly related to the analyte’s equivalent ionic conductance and applies voltage, and is the primary
mechanism of separation.
3.1.6 hydrodynamic sampling, n—a sample introduction technique in which the injection side of the capillary with electrolyte is
immersed into sample solution and then a positive pressure difference is applied.
3.1.6.1 Discussion—
Nanolitres of sample are introduced into the capillary without analyte bias effects.
FIG. 1 Pictorial Diagram of Charged and Neutral Species Mobilities in CE
Available 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.
D7882 − 20
3.1.7 migration time, n—the time required for a specific analyte to migrate through the capillary to the detector.
3.1.7.1 Discussion—
The migration time in capillary electrophoresis is analogous to retention time in chromatography.
4. Summary of Test Method
4.1 A PTA sample is dissolved in ammonium hydroxide solution. The 4-CBA, p-TOL and PTA dissociate and become homologous
ions under basic conditions. A fixed amount of this solution is introduced into the capillary using hydrodynamic sampling. A
voltage is applied to the capillary to separate the impurities, 4-CBA, and p-TOL, from PTA. External standard calibration is used
for quantification.
5. Significance and Use
5.1 The presence of 4-CBA and p-TOL in PTA used for the production of polyester is undesirable because they can slow down
the polymerization process; and 4-CBA is also imparting coloration to the polymer due to thermal instability.
5.2 Determining the amount of 4-CBA and p-TOL remaining from the manufacture of PTA is often required. This test method is
suitable for setting specifications and for use as an internal quality control where these products are produced or used.
5.3 This test method is intended as an alternative to the HPLC method for determination of 4-CBA and p-TOL in PTA. The major
benefits of CE are speed, simplicity, reduced reagent consumption and operating costs.
6. Apparatus
6.1 Capillary Electrophoresis System—The system consists of the following components, as shown in Fig. 2 or equivalent:
6.1.1 High Voltage Power Supply, capable of generating voltage between 0 and 30 kV with the capability of working in a constant
voltage mode.
6.1.2 Covered Sample Carousel, to prevent environmental contamination of the samples and electrolytes during a multi-sample
batch analysis.
6.1.3 Sample Introduction Mechanism, capable of hydrodynamic sampling technique.
FIG. 2 Typical Instrumental Setup
D7882 − 20
6.1.4 Capillary Purge Mechanism, to purge the capillary after every analysis with fresh electrolyte to eliminate any interference
from the previous sample matrix, and to clean the capillary with sodium hydroxide solution and water.
6.1.5 UV Detector, having the capability of monitoring 200 nm, or equivalent.
6.1.6 Fused Silica Capillary, a 50 to 100 μm (inner diameter) by 375 μm (outer diameter) by 60 cm (length) having a polymer
coating for flexibility, with an uncoated section to act as the cell window for UV detection.
6.1.7 Constant Temperature Compartment, to keep the samples, capillary, and electrolytes at constant temperature.
6.2 Data System, a computer system that can acquire data at 20 points/s minimum, express migration time in minutes to three
decimal places.
6.3 Sample Filter, a disposable syringe filter made of cellulose acetate, with a pore size between 0.22 and 0.45 μm, and is
chemically inert to aqueous solutions, is recommended for the removal of particulate matter from the sample solution.
6.4 pH Meter, consisting of a glass-calomel double electrode, used to determine pH values of the solutions.
7. Reagents and Materials
7.1 Purity of Reagents—Unless otherwise indicated, it is intended that all reagents shall conform to the reagent grade specification
for analytical reagents of the American Chemical Society, where such specifications are available. Other grades may be used,
provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the performance or
accuracy of the determination. Reagent chemicals shall be used for all tests.
NOTE 1—Calibration and detection limits of this test method can be biased 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 Water—Unless otherwise indicated, references to water shall be understood to mean Type 1 reagent water conforming
to or exceeding Specification D1193. Freshly drawn water should be used for preparation of all stock and working standards,
electrolytes, and solutions.
7.7 PTA Standard for Calibration—A certified PTA calibration standard with known amounts of 4-CBA and p-TOL is required.
If it is not commercially available, please refer to Annex A1 for determining the concentrations of 4-CBA and p-TOL in a PTA
sample. The calibrated PTA sample can be served as a PTA calibration standard.
7.8 Sodium Hydroxide Solution (0.5 mol/L sodium hydroxide)—Dissolve approximately 20 g of sodium hydroxide in a 1 L plastic
volumetric flask and dilute to 1 L with water.
7.9 Ammonium Hydroxide Solution (2.5 % (m/m) ammonium hydroxide solution)—Add approximately 50 mL 25 % (m/m)
ammonium hydroxide solution in a 500-mL volumetric flask and dilute to 500 mL with water.
7.10 Electrolyte Solution, Working in Normal Voltage Mode (50 mM sodium 1-heptanesulfonate and 10 mM trisodium
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D7882 − 20
phosphate)—Dissolve approximately 0.50 g sodium 1-heptanesulfonate and 0.19 g sodium phosphate tribasic dodecahydrate in a
50-mL volumetric flask and dilute to 50 mL with water. Filter and degas the solution before use.
8. Hazards
8.1 Consult current federal regulations, supplier’s Safety Data Sheets, and local regulations for all materials used in this test
method.
9. Sampling
9.1 Use only representative samples obtained as described in EN ISO 8213, unless otherwise specified.
10. Preparation of Apparatus
10.1 Set up the CE and data system according to the manufacturer’s instructions and adjust the instrument to the conditions
described in Table 1 with the following procedures.
10.2 Program the CE system to maintain a constant temperature. Fill the electrolyte reservoirs with fresh electrolyte working
solution, and allow 10 min for thermal equilibrat
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