ASTM D7883-20

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: D7883 − 19 D7883 − 20
Standard Test Method for
Determination of 4-Carboxybenzaldehyde and p-Toluic Acid
in Purified Terephthalic Acid by Weak Anion Exchange High
Performance Liquid Chromatography
This standard is issued under the fixed designation D7883; 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 the 4-Carboxybenzaldehyde (4-CBA) and p-Toluic acid (p-TOL) in purified
terephthalic acid (PTA) by weak anion exchange high performance liquid chromatography (HPLC). This method is applicable for
4-CBA from 2 to 500 mg/kg and for p-TOL from 10 to 500 mg/kg, respectively.
1.2 In determining the conformance of the test results using this method to applicable specification, 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
E682 Practice for Liquid Chromatography Terms and Relationships
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 D7883 – 13.D7883 – 19. DOI: 10.1520/D7883-19.10.1520/D7883-20.
This standard is based on SH/T 1612.7-1995 Purified terephthalic acid for industrial use—determination of p-Toluic Acid, 4-Carboxybenzaldehyde-HPLC, copyright
SINOPEC, 22 Chaoyangmen North Street, Chaoyang District, Beijing, China 100728. A copy of SH/T 1612.7-1995 may be obtained from China Petrochemical Press,
www.sinopec-press.com.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
D7883 − 20
2.3 Other Document:
OSHA Regulations, 29 CFR paragraphs 1910.1000 and 1910.1200
3. Summary of Test Method
3.1 Weak Anion Exchange HPLC Method—PTA sample is dissolved in ammonium hydroxide solution. After pH adjustment, a
fixed volume of this solution is injected into a high performance liquid chromatograph equipped with a UV detector. An
anion-exchange column is used to separate the impurities 4-CBA and p-TOL from PTA. The external standard calibration is used
for quantification.
4. Significance and Use
4.1 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.
4.2 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 could be used as an internal quality control tool where these products are produced or are
used.
5. Apparatus
5.1 High Performance Liquid Chromatograph (HPLC)—anyAny HPLC capable of pumping the mobile phase at flow rates
between 0.1 and 2.0 mL/min, with a pressure between 0 and 40 MPa and a pulsation of less than 1 % 1 % full scale deflection
under the test conditions described in Table 1. The S/N (signal to noise) ratio should be 3:1 or greater for 2 mg/kg 4-CBA and 10
mg/kg p-TOL.
5.2 Sample Injection System—System, capable of injecting 1 to 25 μL, using either partial or full loop mode, with a repeatability
of 61 %.61 %.
5.3 Detector, Variable Wavelength Ultraviolet Photometric Detector (VWD), Multi-wavelength Detector, or Photometric Diode
Array Detector (PDA), capable of operating at 236 and 258 nm.
5.4 Column Oven—Oven, any suitable HPLC column oven (block heating or air circulating) capable of maintaining a constant
temperature of 61°C within the range of 20 to 70°C.
5.5 Chromatography Data System.
5.6 HPLC Columns:
TABLE 1 Recommended Operating Conditions
Column Weak Alkali Anion Exchange
Stationary phase (-NMe ) chemically bonded silica
Particle size 3 μm
Material of column stainless steel
Length of column 50 mm
Inner diameter 4–5 mm
0.1 mol/L NH H PO
4 2 4
Mobile phase solution:acetonitrile
(or methanol) =9:1
Flow rate 0.8–1.2 mL/min
258 nm for 4-CBA
UV detector
236 nm for p-TOL
Injection amount 20 μL
Column temperature 30–40°C
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D7883 − 20
5.6.1 Guard Column—aA stainless steel column placed in front of the analytical column is recommended. A column, packed with
the same stationary phase as the analytical column, 3 to 5 mm ID and 50 to 100 mm length, has been found to be satisfactory. Other
hydrophilic chemically-bonded silica stationary phases can also be used.
5.6.2 Analytical Column—aA stainless steel HPLC column packed with amino-bonded silica stationary phase is suitable. See
Table 1 for recommended operating conditions.
5.7 Analytical Balance—Balance, readable to 60.0001 g.
5.8 pH Meter.
5.9 Sample Filter—aA 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.
5.10 Vacuum Filter—Filter, capable of filtering mobile phase.
6. Reagents and Materials
6.1 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.
6.2 Ammonium Dihydrogen Phosphate—(Warning—Ammonium dihydrogen phosphate may cause irritation with only minor
residual injury.)
6.3 Ammonium Hydroxide, 25 to 28 % (wt).
6.4 Phosphoric Acid, ≥82 % (wt).
6.5 Acetonitrile—HPLC grade. (Warning—Acetonitrile is flammable and hazardous in case of skin and eye contact, ingestion or
inhalation.)
6.6 Methanol—HPLC grade. (Warning—Methanol is highly flammable and toxic by inhalation, ingestion or skin contact.)
6.7 Water—HPLC grade.
6.8 Ammonium Hydroxide Solution—ammoniumAmmonium hydroxide mixed with water as 1:1 (V:V).
6.9 Phosphoric Acid Solution—phosphoricPhosphoric acid mixed with water as 1:4 (V:V).
6.10 PTA Calibration Standard—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.
6.11 Mobile Phase:
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.
D7883 − 20
6.11.1 0.1 Mol/L NH H PO Solution: Acetonitrile (or Methanol) = 9:1 (v/v)—Dissolve approximately 11.50 g of ammonium
4 2 4
dihydrogen phosphate in 850 mL of water, adjust pH to 4.3 by using phosphoric acid solution. Transfer the resulting solution to
a 1000 mL volumetric flask, add 100 mL of acetonitrile or methanol, dilute with water to the mark.
NOTE 2—It is recommended to degas and filter the mobile phase before use. Degassing can be done conveniently, on-line or off-line by helium sparging,
vacuum degassing or ultrasonic agitation.
7. Hazards
7.1 Consult current federal regulations, supplier’s Safety Data Sheets, and local regulations for all materials used in this test
method.
8. Sampling, Test Specimens, and Test Units
8.1 Use only representative samples obtained as described in EN ISO 8213, unless otherwise specified.
9. Preparation of Apparatus
9.1 Set up the pump, sample injection system, column, oven, detector, and chromatography data system in accordance with the
manufacturer’s instructions. Adjust the instrument to the conditions described in Table 1, allowing sufficient time for the equipment
to reach equilibrium which is indicated by a stable horizontal baseline. For a new column, four to six hours of equilibration time
may be required.
NOTE 3—A gradient mobile phase can also be used for improving chromatograph.
10. Calibration
10.1 Weigh, to the nearest 0.0001 g, about 0.5 g of PTA standard in a 25 mL beaker, add 3 mL of ammonium hydroxide solution
and 7 mL water, to dissolve PTA completely. Adjust the pH value of the solution
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