ASTM D7504-23

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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: D7504 − 21 D7504 − 23
Standard Test Method for
Trace Impurities in Monocyclic Aromatic Hydrocarbons by
Gas Chromatography and Effective Carbon Number
This standard is issued under the fixed designation D7504; 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 total nonaromatic hydrocarbons and monocyclic aromatic hydrocarbons in
benzene, toluene, ethylbenzene, p-xylene, o-xylene, styrene and mixed xylenes by gas chromatography. The purity of benzene,
toluene, ethylbenzene, p-xylene, o-xylene, styrene and mixed xylenes is also calculated. Similar test methods, using the internal
standard calibration technique and the external standard calibration technique, are Test Methods D2360, D3797, D4492, D5060,
D5135, D5917, andand D5917 D6563respectively.
1.2 The limit of detection (LOD) is 0.0002 mass % and limit of quantitation (LOQ) is 0.0006 mass % for impurities in toluene,
mixed xylenes, p-xylene, o-xylene, ethylbenzene, benzene, and styrene.
1.3 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.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
1.6 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:
D1555M Test Method for Calculation of Volume and Weight of Industrial Aromatic Hydrocarbons and Cyclohexane [Metric]
D2360 Test Method for Trace Impurities in Monocyclic Aromatic Hydrocarbons by Gas Chromatography (Withdrawn 2016)
D3437 Practice for Sampling and Handling Liquid Cyclic Products
D3797 Test Method for Analysis of o-Xylene by Gas Chromatography (Withdrawn 2014)
D4492 Test Method for Analysis of Benzene by Gas Chromatography (Withdrawn 2018)
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 D16.01 on Benzene, Toluene, Xylenes, Cyclohexane and Their Derivatives.
Current edition approved July 1, 2021May 1, 2023. Published August 2021May 2023. Originally approved in 2009. Last previous edition approved in 20202021 as
D7504 – 20.D7504 – 21. DOI: 10.1520/D7504-21.10.1520/D7504-23.
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.
The last approved version of this historical standard is referenced on www.astm.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
D7504 − 23
D4790 Terminology of Aromatic Hydrocarbons and Related Chemicals
D5060 Test Method for Determining Impurities in High-Purity Ethylbenzene by Gas Chromatography
D5135 Test Method for Analysis of Styrene by Capillary Gas Chromatography
D5136 Specification for High Purity p-Xylene
D5211 Specification for Xylenes for p-Xylene Feedstock
D5917 Test Method for Trace Impurities in Monocyclic Aromatic Hydrocarbons by Gas Chromatography and External
Calibration
D6563 Test Method for Benzene, Toluene, Xylene (BTX) Concentrates Analysis by Gas Chromatography (Withdrawn 2018)
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
E260 Practice for Packed Column Gas Chromatography
E355 Practice for Gas Chromatography Terms and Relationships
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E1510 Practice for Installing Fused Silica Open Tubular Capillary Columns in Gas Chromatographs
2.2 Other Document:
OSHA Regulations, 29 CFR paragraphs 1910.1000 and 1910.1200
3. Terminology
3.1 See Terminology D4790 for definitions of terms used in this test method.
4. Summary of Test Method
4.1 The specimen to be analyzed is injected into a gas chromatograph equipped with a flame ionization detector (FID) and a
capillary column. The peak area of each component is measured and adjusted using effective carbon number (ECN) correction
factors. The concentration of each component is calculated based on its relative percentages of total adjusted peak area and
normalized to 100.0000 %.
5. Significance and Use
5.1 Determining the type and amount of hydrocarbon impurities remaining from the manufacture of toluene, mixed xylenes,
p-xylene, o-xylene, ethylbenzene, benzene, and styrene used as chemical intermediates and solvents is often required. This test
method is suitable for setting specifications and for use as an internal quality control tool where these products are produced or
are used. Typical impurities are: alkanes containing 1 to 10 carbons atoms, benzene, toluene, ethylbenzene (EB), xylenes, and
aromatic hydrocarbons containing nine carbon atoms or more.
5.2 This method may not detect all components and there may be unknown components that would be assigned inappropriate
correction factors and thus, the results may not be absolute.
6. Interferences
6.1 The complete separation of p-xylene from ethylbenzene, or ethylbenzene and m-xylene from p-xylene can be difficult when
either ethylbenzene or p-xylene is analyzed, respectively. The separation can be considered adequate if the distance from the
baseline to the valley between the two peaks is not greater than 50 % of the peak height of lower of the two peaks.
7. Apparatus
7.1 Chromatographic data system is required.
7.2 Columns—The choice of column is based on resolution requirements. Any column may be used that is capable of resolving
all significant impurities from the major component. The column and conditions described in Table 1 have been used successfully
and shall be used as a referee in cases of dispute. A 60 m column with an internal diameter of 0.32 mm and a film thickness of
0.50 μm crosslinked polyethylene glycol may improve resolution.
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.
Scanlon, J. T. and Willis, D. E., “Calculation of Flame Ionization Detector Relative Response Factors Using the Effective Carbon Number Concept,” Journal of
Chromatographic Science, Vol. 23, August 1985, pp. 333–339.
D7504 − 23
TABLE 1 Recommended Method Parameters
Inlet Split
Temperature, °C 270
Column:
Tubing fused silica
Length, m 60
Internal diameter, mm 0.32
Stationary phase crosslinked polyethylene
glycol
Film thickness, μm 0.25
Column temperature program
Initial temperature, °C 60
Initial time, min 10
Programming rate, °C/min 5
Final, °C 150
Time 2, min 10
Carrier gas helium or hydrogen
Linear velocity, cm/s at 145°C 20 helium or 45 hydrogen
Linear velocity, cm/s at 145 °C 20 helium or 45 hydrogen
Split ratio 100:1
Sample size, μL 0.6
Detector: flame ionization
Temperature, °C 300
Analysis time, min 38
7.3 Gas Chromatograph—Any instrument having a flame ionization detector and a splitter injector suitable for use with a fused
silica capillary column may be used, provided the system has sufficient sensitivity, linearity, and range to determine 0.0001 mass %,
while not exceeding the full scale of either the detector or the electronic integration for the major component. It shall have a split
injection system that will not discriminate over the boiling range of the samples analyzed. The system should be capable of
operating at conditions given in Table 1.
7.4 Injector—The specimen must be precisely and repeatably injected into the gas chromatograph. An automatic sample injection
devise is highly recommended.
7.5 Syringe—Chromatographic, capable of delivering appropriate μL volumes.
8. Reagents and Materials
8.1 Purity of Reagent—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Reagents with an establish purity greater than ACS reagent grade may be used.
8.1.1 Alpha-methylstyrene (AMS) CAS 98-83-9,
8.1.2 Benzene CAS 71-43-2,
8.1.3 Cumene (isopropylbenzene) CAS 98-82-8,
8.1.4 1,4-dioxane CAS 123-91-1,
8.1.5 Ethylbenzene CAS 100-41-4,
8.1.6 Ethyltoluene CAS 622-96-8,
8.1.7 m-xylene CAS 108-38-3,
8.1.8 n-propylbenzene CAS 103-65-1,
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.
D7504 − 23
8.1.9 o-xylene CAS 95-47-6,
8.1.10 p-diethylbenzene (PDEB) CAS 105-05-5,
8.1.11 p-xylene CAS 106-42-3,
8.1.12 Phenylacetylene (ethynylbenzene) CAS 536-74-3,
8.1.13 2-propenylbenzene CAS 300-57-2,
8.1.14 sec-butylbenzene CAS 135-98-8,
8.1.15 Styrene CAS 100-42-5,
8.1.16 tert-butylbenzene CAS 98-06-6,
8.1.17 Toluene CAS 108-88-3, and
8.1.18 Trimethylbenzene CAS 108-67-8.
8.2 Carrier Gas, Makeup Gas and Detector Gases 99.999 % Pure. Oxygen in carrier gas less than 1 ppm, less than 0.5 ppm is
preferred. Purify carrier, makeup and detector gases to remove oxygen, water, and hydrocarbons.
8.3 Air for the FID should contain less than 0.1 ppm total hydrocarbon.
8.4 Equipment Set-up Check Sample
8.4.1 High Purity p-xylene (99.9999 mass % or greater purity)—Most p-xylene is available commercially at a purity less than 99.9
mass %, but should be purified by recrystallization. To prepare 2 L of high-purity p-xylene, begin with approximately 6 L of
1 3
reagent-grade p-xylene and cool in an explosion-proof freezer at between –10 °C to +10 °C until approximately ⁄2 to ⁄4 of the
p-xylene has frozen. Remove the sample and decant the liquid portion. Allow the p-xylene to thaw and repeat the crystallization
step on the remaining sample until the p-xylene is free of contamination (no peaks detected other than p-xylene) as indicated by
gas chromatography.
8.4.2 Prepare peak identification material by pipetting the following amounts into a 250 mL flask:
100 mL m-xylene,
10 mL alpha methylstyrene,
10 mL benzene,toluene,
10 mL cumene,
10 mL 1,4-dioxane,
10 mL ethylbenzene,
10 mL phenylacetylene,
10 mL styrene,
10 mL o-xylene,
Mix thoroughly.
8.4.3 Prepare sensitivity check material by:
8.4.3.1 Partially fill a 500 mL volumetric flask with high purity p-xylene.
8.4.3.2 Add 1 mL of toluenebenzene to the 500 mL volumetric flask.
8.4.3.3 Fill the 500 mL volumetric flask to the mark with high purity p-xylene and mix thoroughly.
8.4.4 Preparation of the final equipment set-up check sample:
D7504 − 23
8.4.4.1 Partially fill a 500 mL volumetric flask with high purity p-xylene.
8.4.4.2 Pipette 1 mL of the peak identification material prepared in 8.4.2 into the 500 mL volumetric flask.
8.4.4.3 Use a 10 mL burette to add 1.1 mL of the sensitivity check material prepared in 8.4.3 to the 500 mL volumetric flask.
8.4.4.4 Dilute to volume with high purity p-xylene and mix thoroughly.
8.4.5 Impurities that are not present in the samples being analyzed may be omitted from the check sample. Impurities not included
in the check sample may be added. However, m-xylene and toluene must be included.
8.4.6 The equipment set-up check sample may be purchased if available.
8.4.7 The purpose of the set-up check sample is to help determine the retention time of the various components and that the
p-xylene and m-xylene are adequately separated. This sample should not be used for calibration.
NOTE 1—The benzene,toluene, cumene, 1,4-dioxane, alpha methylstyrene, phenylacetylene, o-xylene, and styrene are included to aid in peak
identification.
NOTE 2—The amount of benzene was increased to help ensure the retention time of benzene is properly determined. There are a number of non-aromatics
with retention times near benzene.
NOTE 2—The m-xylene is included to determine that adequate resolution of m-xylene from p-xylene occurs.
NOTE 3—TolueneBenzene is included to determine that the equipment set-up has the sensitivity specified in this standard.
9. Hazards
9.1 Consult current OSHA regulations, supplier’s Safety Data Sheets, and local regulations for all materials used in this test
method.
10. Sampling
10.1 Sample the material in accordance with Practice D3437.
11. Preparation of Apparatus
11.1 Follow manufacturer’s instructions for mounting and conditioning the column into the chromatograph and adjusting the
instrument to the conditions described in Table 1, allowing sufficient time for the equipment to reach equilibrium. See Practices
E260, E355, and E1510 for additional information on gas chromatography practices and terminology.
12. Calibration
12.1 Prior to implementation of the ECN method, a laboratory should demonstrate that the equipment is set up properly using an
equipment set-up check sample. This sample should be used to determine:determine retention times of each component, and that
the separation of m-xylene from p-xylene is satisfactory. See 6.1 for the definition of an adequate separation.
12.2 The LOD for this standard is 0.0002 mass %. The equipment set-up check sample contains 0.0004 mass % toluene.benzene.
Acceptable results are 0.0001 mass % to 0.0008 mass %.
NOTE 4—TolueneBenzene was chosen because there are no other peaks near the toluene peak.this is the trace impurity that typically is the lowest level
impurity and is of significant environmental concern.
13. Procedure
13.1 Warning—It is important to check the column resolution. When different types of samples, particularly low purity samples
are injected, the front of the column will become contaminated. Eventually the column resolution will be reduced to the point that
the integration system will not separate some peaks, particularly m-xylene from p-xylene.
D7504 − 23
NOTE 5—Contamination on the front end of the column can be minimized by baking out the column on a periodic basis or eliminated by cutting off a
few inches from the front end.
NOTE 6—It is helpful to dedicate GCs for each high purity product and others GCs for samples with significant impurities.
13.2 Bring the sample to room temperature.
13.3 Analyze the equipment set-up check sample as needed to ensure adequate resolution of m-xylene from p-xylene, that the gas
chromatograph has the sensitivity specified by this standard, and that all the peaks are properly identified.
13.4 Inject an appropriate amount of sample into the instrument.
13.5 Review the chromatographic data system result. Measure the area of all peaks. The non-aromatics fraction includes all peaks
TABLE 2 Effective Carbon Number Correction Factors and
Density
ECN
Component Correction Density at 20°C20 °C
A
Factor
B
Non-Aromatics 1.0000 0.7255 (average)
C
Benzene 0.9095 0.8780
C
Toluene 0.9195 0.8658
D
1,4-dioxane 3.0774 1.0329
C
Ethylbenzene 0.9271 0.8658
C
p-xylene 0.9271 0.8597
C
m-xylene 0.9271 0.8630
C
Cumene 0.9329 0.8605
C
o-xylene 0.9271 0.8786
H
n-propylbenzene 0.9329 0.8620
E
C Aromatics 0.9329 0.8715 average
tert-butylbenzene 0.9376 0.867
I
tert-butylbenzene 0.9376 0.8669
sec-butylbenzene 0.9376 0.863
J
sec-butylbenzene 0.9376 0.8580
C
Styrene 0.9210 0.9048
K
Ethyltoluene 0.9329 0.861
E
C Aromatics 0.9376 0.8694 average
E
p-diethylbenzene 0.9376 0.8620
(PDEB)
F
Phenylacetylene 0.8296 0.9300
F
Alpha-methylstyrene 0.9276 0.9077
(AMS)
Trimethylbenzene 0.9329 0.8637
L
Trimethylbenzene 0.9329 0.8758
2-propenylbenzene 0.9276 0.893
G
Unknown 0.931
A
Correction factors are relative to n-heptane.
B
DS # 4A Physical Constants of Hydrocarbons C through C , ASTM, 1971.
1 10
Average of hexane, methylcyclopentane, methylcyclohexane, heptane, and
ethylcyclopentane.
C
Test Method D1555M.
D
Keith, L. H., Walters, DD. B., Compendium of Safety Data Sheets for Res
...