ASTM D7536-20

Standard Test Method for Chlorine in Aromatics by Monochromatic Wavelength Dispersive X-ray Fluorescence Spectrometry

SIGNIFICANCE AND USE
5.1 This test method provides for the precise measurement of the chlorine content of aromatics with minimal sample preparation and analyst involvement. The typical time for each analysis is five or ten minutes.  
5.2 Knowledge of the chlorine content of aromatics is important for process control as well as the prediction and control of operational problems such as unit corrosion and catalyst poisoning, and in the blending of products to commodity specifications.  
5.3 Various federal, state, and local agencies regulate the chlorine content of some petroleum products, including aromatics. Unbiased and precise determination of chlorine in aromatics is critical to compliance with regulatory standards.  
5.4 When the elemental composition of the samples differ significantly from the calibration standards used to prepare the calibration curve, the cautions and recommendation in Section 6 should be carefully observed.
SCOPE
1.1 This test method covers the determination of chlorine by monochromatic wavelength-dispersive X-ray fluorescence (MWDXRF) spectrometry in aromatic hydrocarbons, their derivatives, and related chemicals.  
1.2 This test method is applicable to samples with chlorine concentrations to 10 mg/kg. Higher chlorine concentrations can be determined by quantitatively diluting the sample with a suitable solvent. The limit of detection (LOD) is 0.2 mg/kg and the limit of quantitation is 0.7 mg/kg. With careful analytical technique or the measurement of replicates, or both, this method can be used to successfully analyze concentrations below the LOD.
Note 1: The maximum is the highest concentration from the interlaboratory study (ILS) and the LOD and LOQ were calculated from Performance Testing Program (PTP) data. See Table 3.  
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. For specific hazard information, see Section 9.  
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.

General Information

• Status: Published
• Publication Date: 14-Aug-2020
• ICS: 71.080.15 - Aromatic hydrocarbons
• Technical Committee: D16 - Aromatic, Industrial, Specialty and Related Chemicals
• Drafting Committee: D16.04 - Instrumental Analysis

Relations

• Replaces: ASTM D7536-16 - Standard Test Method for Chlorine in Aromatics by Monochromatic Wavelength Dispersive X-ray Fluorescence Spectrometry
• Effective Date: 15-Aug-2020
• 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 D4790-14 - Standard Terminology of Aromatic Hydrocarbons and Related Chemicals
• Effective Date: 01-Jul-2014
• 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 D4790-11 - Standard Terminology of Aromatic Hydrocarbons and Related Chemicals
• Effective Date: 01-Feb-2011
• Refers: ASTM D3437-11 - Standard Practice for Sampling and Handling Liquid Cyclic Products
• Effective Date: 01-Jan-2011
• Refers: ASTM D3437-10 - Standard Practice for Sampling and Handling Liquid Cyclic Products
• Effective Date: 01-Jun-2010
• 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 D3437-08 - Standard Practice for Sampling and Handling Liquid Cyclic Products
• Effective Date: 01-Jun-2008
• Refers: ASTM D4790-07 - Standard Terminology of Aromatic Hydrocarbons and Related Chemicals
• Effective Date: 15-Jul-2007
• 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

Overview

ASTM D7536-20, issued by ASTM International, specifies the standard test method for determining chlorine content in aromatic hydrocarbons and related chemicals using monochromatic wavelength-dispersive X-ray fluorescence spectrometry (MWDXRF). This method is designed for precise and unbiased chlorine analysis with minimal sample preparation and user intervention. Typical analysis times are five to ten minutes, making it efficient for both routine and high-throughput applications.

Measuring chlorine in aromatics is critical in petroleum refining, chemical processing, and where regulatory and product specifications must be met. Chlorine determination is essential for process control, the prediction and management of corrosion and catalyst poisoning, and ensuring regulatory compliance.

Key Topics

• Chlorine Analysis in Aromatics: Fast, accurate quantification of chlorine in aromatics, aromatic derivatives, and related compounds with concentrations from 0.2 mg/kg (limit of detection) up to 10 mg/kg. Higher concentrations are measurable with appropriate sample dilution.
• MWDXRF Technique: Utilizes a monochromatic X-ray source to excite chlorine atoms in the sample. The emitted characteristic X-ray radiation is measured and correlated to chlorine content using a well-defined calibration curve.
• Calibration and Quality Control: Requires careful calibration using standards matching the matrix of test samples and regular verification with known check samples. ASTM D7536-20 offers guidance on the use of calibration standards and quality control procedures to assure accuracy.
• Regulatory Compliance: Supports meeting federal, state, and local regulations concerning the maximum allowable chlorine in petroleum products and chemicals.
• Precision and Repeatability: Interlaboratory studies confirm the method's high precision and reproducibility over the specified measurement range.
• Sample Preparation and Safety: Minimal handling of chemicals, with specific recommendations for sample containment and handling to maximize safety and reliability.

Applications

• Petroleum Refining: Monitoring chlorine content in aromatics such as benzene, toluene, and xylene is essential to avoid unit corrosion, catalyst poisoning, and to meet commodity specifications for fuel and feedstock blending.
• Chemical Manufacturing: Used in quality assurance for producers and users of aromatic hydrocarbons and their derivatives to ensure purity and regulatory compliance.
• Regulatory Bodies and Environmental Agencies: Ensures unbiased, precise reporting of chlorine content for compliance with chlorinated compound regulations.
• Laboratory and Quality Control: Fast analysis cycle supports integration into QA/QC programs for continuous process monitoring and product release testing.
• Research and Development: Applied in R&D settings that require accurate chlorine measurement for process optimization or formulation work in specialty chemicals.

Related Standards

• ASTM D3437: Practice for Sampling and Handling Liquid Cyclic Products
• ASTM D4790: Terminology of Aromatic Hydrocarbons and Related Chemicals
• ASTM D6809: Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
• ASTM E29: Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• ASTM E691: Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

These referenced standards support best practices in sampling, terminology, QA/QC, and data handling, ensuring consistent and reliable implementation of ASTM D7536-20.

---

Keywords: ASTM D7536-20, chlorine in aromatics, monochromatic X-ray fluorescence, MWDXRF, aromatic hydrocarbon analysis, spectrometry, chlorine quantification, petroleum product testing, regulatory compliance, quality control.

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: D7536 − 20
Standard Test Method for
Chlorine in Aromatics by Monochromatic Wavelength
Dispersive X-ray Fluorescence Spectrometry
This standard is issued under the fixed designation D7536; 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* 2. Referenced Documents
1.1 Thistestmethodcoversthedeterminationofchlorineby 2.1 ASTM Standards:
monochromatic wavelength-dispersive X-ray fluorescence D3437 Practice for Sampling and Handling Liquid Cyclic
(MWDXRF) spectrometry in aromatic hydrocarbons, their Products
derivatives, and related chemicals. D4790 Terminology ofAromatic Hydrocarbons and Related
Chemicals
1.2 This test method is applicable to samples with chlorine
D6809 Guide for Quality Control and Quality Assurance
concentrations to 10 mg/kg. Higher chlorine concentrations
Procedures for Aromatic Hydrocarbons and Related Ma-
can be determined by quantitatively diluting the sample with a
terials
suitablesolvent.Thelimitofdetection(LOD)is0.2mg/kgand
E29 Practice for Using Significant Digits in Test Data to
the limit of quantitation is 0.7 mg/kg. With careful analytical
Determine Conformance with Specifications
technique or the measurement of replicates, or both, this
E691 Practice for Conducting an Interlaboratory Study to
method can be used to successfully analyze concentrations
Determine the Precision of a Test Method
below the LOD.
2.2 Other Documents:
NOTE 1—The maximum is the highest concentration from the inter-
OSHA Regulations, 29 CFR paragraphs 1910.1000 and
laboratory study (ILS) and the LOD and LOQ were calculated from
1910.1200
Performance Testing Program (PTP) data. See Table 3.
1.3 In determining the conformance of the test results using
3. Terminology
this method to applicable specifications, results shall be
3.1 See Terminology D4790 for definitions of terms used in
rounded off in accordance with the rounding-off method of
Practice E29. this test method.
1.4 The values stated in SI units are to be regarded as
4. Summary of Test Method
standard. No other units of measurement are included in this
standard. 4.1 A monochromatic X-ray beam with a wavelength suit-
able to excite the K-shell electrons of chlorine is focused onto
1.5 This standard does not purport to address all of the
a test specimen contained in a sample cell (see Fig. 1). The
safety concerns, if any, associated with its use. It is the
fluorescent Kα radiation at 0.473 nm (4.73Å) emitted by
responsibility of the user of this standard to establish appro-
chlorine is collected by a fixed monochromator (analyzer).The
priate safety, health, and environmental practices and deter-
intensity (counts per second) of the chlorine X-rays is mea-
mine the applicability of regulatory limitations prior to use.
sured using a suitable detector and converted to the concen-
For specific hazard information, see Section 9.
tration of chlorine (mg/kg) in a test specimen using a calibra-
1.6 This international standard was developed in accor-
tion equation. Excitation by monochromatic X-rays reduces
dance with internationally recognized principles on standard-
background, simplifies matrix correction and increases the
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee D16 on contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Aromatic, Industrial, Specialty and Related Chemicals and is the direct responsi- Standards volume information, refer to the standard’s Document Summary page on
bility of Subcommittee D16.04 on Instrumental Analysis. the ASTM website.
Current edition approved Aug. 15, 2020. Published August 2020. Originally AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
approved in 2009. Last previous edition approved in 2016 as D7356 – 16. DOI: 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
10.1520/D7536-20. 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
D7536 − 20
FIG. 1 Schematic of the MWDXRF Analyzer
signal/background ratio compared to polychromatic excitation 7. Apparatus
used in conventional WDXRF techniques.
7.1 Monochromatic Wavelength Dispersive X-ray Fluores-
cence (MWDXRF) Spectrometer , equipped for X-ray detec-
5. Significance and Use
tion at 0.473 nm (4.73Å).Any spectrometer of this type can be
used if it includes the following features, and the precision of
5.1 This test method provides for the precise measurement
test results are in accordance with the values described in
of the chlorine content of aromatics with minimal sample
Section 16.
preparation and analyst involvement.The typical time for each
7.1.1 X-ray Source, capable of producing X-rays to excite
analysis is five or ten minutes.
chlorine. X-ray tubes capable of producing Rh Lα,PdLα,Ag
5.2 Knowledge of the chlorine content of aromatics is
Lα,TiKα,ScKα, and Cr Kα radiation are recommended for
important for process control as well as the prediction and
this purpose.
control of operational problems such as unit corrosion and
7.1.2 Incident-beam Monochromator, capable of focusing
catalyst poisoning, and in the blending of products to com-
andselectingasinglewavelengthofcharacteristicX-raysfrom
modity specifications.
the source onto the specimen.
7.1.3 Optical Path, designed to minimize the absorption
5.3 Various federal, state, and local agencies regulate the
along the path of the excitation and fluorescent beams using a
chlorine content of some petroleum products, including aro-
vacuum or a helium atmosphere. The calibration and test
matics. Unbiased and precise determination of chlorine in
measurements must be done with identical optical paths,
aromatics is critical to compliance with regulatory standards.
including vacuum or helium pressure.
5.4 When the elemental composition of the samples differ
7.1.4 Monochromator, suitable for dispersing chlorine Kα
significantly from the calibration standards used to prepare the
X-rays.
calibration curve, the cautions and recommendation in Section
7.1.5 Detector, designed for efficient detection of chlorine
6 should be carefully observed.
Kα X-rays.
7.1.6 Single-Channel Analyzer, an energy discriminator to
6. Interferences
monitor only chlorine radiation.
6.1 Differences between the elemental composition of test
7.2 Removable Sample Cell, any specimen holder compat-
samples and the calibration standards can result in biased
ible with the geometry of the MWDXRF spectrometer and
chlorine determinations. For aromatics within the scope of this
designedtouseX-raytransparentfilm(see7.3)toholdaliquid
test method, matrix correction can be avoided with a proper
specimen with a minimum depth of 3 mm. The sample cell
choice of calibrants. To minimize any bias in the results, use
must not leak when fitted with X-ray transparent film. A
calibration standards prepared from chlorine-free base materi-
disposable cell is recommended.
als of the same or similar elemental composition as the test
samples.
The sole source of supply of the apparatus known to the committee at this time
is X-Ray Optical Systems, Inc., 15 Tech Valley Drive, East Greenbush, NY, 12061.
If you are aware of alternative suppliers, please provide this information to ASTM
Bertin, E. P., Principles and Practices of X-ray Spectrometric Analysis, Plenum International Headquarters. Your comments will receive careful consideration at a
Press, New York, 1975, pp. 115-118. meeting of the responsible technical committee, which you may attend.
D7536 − 20
determination, a lower cost material is suggested for daily use.Any stable
7.3 X-ray Transparent Film, for containing and supporting
material can be used for daily monitoring of drift.
the test specimen in the sample cell (see 7.2) while providing
NOTE 6—The effect of drift correction on the precision and bias of this
a low-absorption window for X-rays to pass to and from the
test method has not been studied.
sample. Any film resistant to chemical attack by the sample,
free of chlorine, and X-ray transparent may be used.
9. Hazards
7.4 Analytical balance capable of reading to 0.0001 g.
9.1 Warning—Exposure to excessive quantities of X-ray
radiation is injurious to health. The operator needs to take
8. Reagents and Materials
appropriate actions to avoid exposing any part of his/her body,
8.1 Purity of Reagents—Reagent grade chemicals shall be
not only to primary X-rays, but also to secondary or scattered
used in all tests. Unless otherwise indicated, it is intended that
radiation that might be present.The X-ray spectrometer should
all reagents conform to the specifications of the Committee on
be operated in accordance with the regulations governing the
Analytical Reagents of the American Chemical Society where
use of ionizing radiation.
such specifications are available. Other grades may be used,
9.2 Consult current OSHA regulations, suppliers’ Safety
provided it is first ascertained that the reagent is of sufficiently
Data Sheets and local regulations for all materials used in this
high purity to permit its use without lessening the accuracy of
test method.
the determination.
8.2 Calibration-Check Samples, for verifying the accuracy
10. Sampling and Handling
of a calibration. The check samples must have known chlorine
10.1 Sample the material in accordance with Practice
content and not be used in determining the calibration curve.A
D3437.
standard from the same reliable and consistent source of
calibration standards used to determine the calibration curve is
10.2 For each sample, an unused piece of X-ray transparent
convenient to check the calibration. film is required for the sample cell. Avoid touching the inside
of the sample cell, any portion of the film exposed to the liquid
8.3 2-Propanol, minimum 99 % purity, for cleaning of
or the X-ray beam, and also avoid touching the instrument
analyzer parts in the sample chamber that may become
window. Oil from fingerprints and wrinkles can generate errors
contaminated with spilled samples and other contaminants.
intheanalysisofchlorine.Therefore,makesurethefilmistaut
8.4 1,2,4-Trichlorobenzene, a high-purity liquid (minimum
and clean to ensure reliable results. It is recommended to use
99 % purity) with a certified chlorine concentration. Use the
canned air to ensure the film and sample cup is dust free prior
certified chlorine concentration when calculating the exact
to assembling sample cell. Use calibration-check samples (see
concentrations of chlorine in calibration standards.
8.2) to verify calibration integrity if the type and thickness of
the window film is changed. After the sample cell is filled,
8.5 Quality-Control Samples, for use in establishing and
monitoringthestabilityandprecisionofananalyticalmeasure- provide a vent above the sample to prevent bowing of the film
by accumulating vapors. When reusable sample cells are used,
ment system (see Section 17). Use homogeneous materials,
similar to samples of interest and available in sufficient thoroughly clean and dry cells before each use. Disposable
sample cells shall not be reused.
quantity to be analyzed regularly for a long period of time.
NOTE 2—Verification of system control through the use of QC samples
10.3 Because impurities and thickness variations can occur
and control charting is highly recommended.
in commercially available transparent films and vary from lot
NOTE 3—Suitable QC samples can be prepared by combining retains of
typical samples. to lot, use calibration-check samples (see 8.2) to verify
calibration integrity after starting each new batch of film.
8.6 Xylene, use a high purity p-xylene HPLC grade and
account for its chlorine content when calculating the chlorine
11. Preparation of Apparatus
concentration of the calibration standards.
11.1 Analyzer Preparation—Ensure that the MWDXRF
8.7 Drift-Monitor Sample (optional), to determine and cor-
analyzer has been installed and put into operation in accor-
rect instrument drift over time (see 12.4, 13.2, and 14.2).
dance with manufacturer’s instructions. Allow sufficient time
Various forms of stable chlorine-containing materials are
for instrument electronics to stabilize. Perform any instrument
suitable drift-correction samples, for example, liquid
checkout procedures required. When possible, the instrument
petroleum, solid, and pressed powder.The count rate displayed
should be run continuously to maintain optimum stability.
bythemonitorsample,incombinationwithaconvenientcount
11.1.1 Use the count time (T) recommended by the instru-
time(T),shallbesufficienttogivearelativestandarddeviation
ment manufacturer for the lowest chlorine concentration ex-
(RSD) of <1 % (see Appendix X1).
pected. The typical time for each measurement is five or ten
NOTE 4—Calibration standards may be used as drift-monitor samples.
minutes.
NOTE 5—Because it is desirable to discard test specimens after each
11.1.2 Alternatively, determine T expected for a desired
count precision by following the procedure in Appendix X1.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, American Chemical Society, Washington,
11.2 Minimizing Analyzer Contamination—Analyzer con-
DC. For suggestions on the testing of reagents not listed by theAmerican Chemical
tamination may lead to falsely high measurement results. To
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
minimize analyzer contamination, perform the following steps
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
copeial Convention, Inc. (USPC), Rockville, MD. at least once each day the analyzer is in use.
D7536 − 20
11.2.1 Clean the portion of the lid that is in contact with the second by dividing total counts by the count time (T) using
top of the sample cell with 2-propanol.Additionally, clean the units of seconds (see 11.1.1 and 11.1.2).
lid after measurement of a sample containing greater than 50
NOTE 7—Due to the linearity of the MWDXRF spectrometer
mg/kg chlorine and prior to the measurement of sample
calibration, it is recommended to calibrate beyond the scope of this test
containing less than 1 mg/kg chlorine. Residue from higher
method in order to minimize negative effects at the lower end of the
calibration of any errors in the preparation of calibration standards. For
concentration samples may contaminate subsequent low con-
example, if one assumes an absolute 1 mg/kg error in the preparation of
centration measurements. Wipe up any visible sample residue
each of the calibration standards, the relative error is minimized in the
after sample measurement.
higher calibration standards (2 % error in the 50 mg/kg standard versus
11.2.2 Clean the primary window with 2-propanol soaked
20 %errorinthe5mg/kgstandard).Ineffect,thehighercalibrationpoints
foam tipped or cotton swab. Shake excess alcohol from swab serve to stabilize the slope of the calibration.
prior to using it for cleaning, as excess alcohol on the swab
12.2.1 Alternately, commercially available calibration stan-
may leave a residue on the primary window when it dries. It is
dards may be used provided their relative uncertainty does not
recommended to use canned air to blow the windo
...

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: D7536 − 16 D7536 − 20
Standard Test Method for
Chlorine in Aromatics by Monochromatic Wavelength
Dispersive X-ray Fluorescence Spectrometry
This standard is issued under the fixed designation D7536; 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 Scope*
1.1 This test method covers the determination of chlorine by monochromatic,monochromatic wavelength-dispersive X-ray
fluorescence (MWDXRF) spectrometry in aromatic hydrocarbons, their derivatives, and related chemicals.
1.2 This test method is applicable to samples with chlorine concentrations from 0.66 mg/kg to 10.07to 10 mg/kg. Higher chlorine
concentrations can be determined by quantitatively diluting the sample with a suitable solvent. In an interlaboratory study, The
limit of detection (LOD) is 0.2 mg/kg and the limit of detection was determined to be 0.18 mg/kg.quantitation is 0.7 mg/kg. With
careful analytical technique or the measurement of replicates, or both, this method can be used to successfully analyze
concentrations below the LOD.
NOTE 1—The maximum is the highest concentration from the interlaboratory study (ILS) and the LOD and LOQ were calculated from Performance
Testing Program (PTP) data. See Table 3.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific hazard information, see Section 9.
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:
D3437 Practice for Sampling and Handling Liquid Cyclic Products
D4790 Terminology of Aromatic Hydrocarbons and Related Chemicals
D6809 Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
This test method is under the jurisdiction of ASTM Committee D16 on Aromatic Hydrocarbons Aromatic, Industrial, Specialty and Related Chemicals and is the direct
responsibility of Subcommittee D16.04 on Instrumental Analysis.
Current edition approved June 1, 2016Aug. 15, 2020. Published July 2016August 2020. Originally approved in 2009. Last previous edition approved in 20092016 as D7356
– 09.16. DOI: 10.1520/D7536-16.10.1520/D7536-20.
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.
*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
D7536 − 20
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 Other Documents:
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 A monochromatic X-ray beam with a wavelength suitable to excite the K-shell electrons of chlorine is focused onto a test
specimen contained in a sample cell (see Fig. 1). The fluorescent Kα radiation at 0.473 nm (4.73Å) emitted by chlorine is collected
by a fixed monochromator (analyzer). The intensity (counts per second) of the chlorine X-rays is measured using a suitable detector
and converted to the concentration of chlorine (mg/kg) in a test specimen using a calibration equation. Excitation by
monochromatic X-rays reduces background, simplifies matrix correction and increases the signal/background ratio compared to
polychromatic excitation used in conventional WDXRF techniques.
5. Significance and Use
5.1 This test method provides for the precise measurement of the chlorine content of aromatics with minimal sample preparation
and analyst involvement. The typical time for each analysis is five or ten minutes.
5.2 Knowledge of the chlorine content of aromatics is important for process control as well as the prediction and control of
operational problems such as unit corrosion and catalyst poisoning, and in the blending of products to commodity specifications.
5.3 Various federal, state, and local agencies regulate the chlorine content of some petroleum products, including aromatics.
Unbiased and precise determination of chlorine in aromatics is critical to compliance with regulatory standards.
5.4 When the elemental composition of the samples differ significantly from the calibration standards used to prepare the
calibration curve, the cautions and recommendation in Section 6 should be carefully observed.
FIG. 1 Schematic of the MWDXRF Analyzer
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.
Bertin, E. P., Principles and Practices of X-ray Spectrometric Analysis, Plenum Press, New York, 1975, pp. 115-118.
D7536 − 20
6. Interferences
6.1 Differences between the elemental composition of test samples and the calibration standards can result in biased chlorine
determinations. For aromatics within the scope of this test method, matrix correction can be avoided with a proper choice of
calibrants. To minimize any bias in the results, use calibration standards prepared from chlorine-free base materials of the same
or similar elemental composition as the test samples.
7. Apparatus
7.1 Monochromatic Wavelength Dispersive X-ray Fluorescence (MWDXRF) Spectrometer , equipped for X-ray detection at 0.473
nm (4.73Å). Any spectrometer of this type can be used if it includes the following features, and the precision of test results are
in accordance with the values described in Section 16.
7.1.1 X-ray Source, capable of producing X-rays to excite chlorine. X-ray tubes capable of producing Rh Lα, Pd Lα, Ag Lα, Ti
Kα, Sc Kα, and Cr Kα radiation are recommended for this purpose.
7.1.2 Incident-beam Monochromator, capable of focusing and selecting a single wavelength of characteristic X-rays from the
source onto the specimen.
7.1.3 Optical Path, designed to minimize the absorption along the path of the excitation and fluorescent beams using a vacuum
or a helium atmosphere. The calibration and test measurements must be done with identical optical paths, including vacuum or
helium pressure.
7.1.4 Monochromator, suitable for dispersing chlorine Kα X-rays.
7.1.5 Detector, designed for efficient detection of chlorine Kα X-rays.
7.1.6 Single-Channel Analyzer, an energy discriminator to monitor only chlorine radiation.
7.2 Removable Sample Cell, any specimen holder compatible with the geometry of the MWDXRF spectrometer and designed to
use X-ray transparent film (see 7.3) to hold a liquid specimen with a minimum depth of 3 mm. The sample cell must not leak when
fitted with X-ray transparent film. A disposable cell is recommended.
7.3 X-ray Transparent Film, for containing and supporting the test specimen in the sample cell (see 7.2) while providing a
low-absorption window for X-rays to pass to and from the sample. Any film resistant to chemical attack by the sample, free of
chlorine, and X-ray transparent may be used.
7.4 Analytical balance capable of reading to 0.0001 g.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents conform to the specifications of the Committee on 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 accuracy of the determination.
8.2 Calibration-Check Samples, for verifying the accuracy of a calibration. The check samples must have known chlorine content
and not be used in determining the calibration curve. A standard from the same reliable and consistent source of calibration
standards used to determine the calibration curve is convenient to check the calibration.
The sole source of supply of the apparatus known to the committee at this time is X-Ray Optical Systems, Inc., 15 Tech Valley Drive, East Greenbush, NY, 12061. If
you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting
of the responsible technical committee, which you may attend.
Reagent Chemicals, American Chemical Society Specifications,ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, American Chemical Society, Washington, D. C. DC. For suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards
for Laboratory Chemicals, BD Ltd., Pole, Dourest, U. K., BDH Ltd., Poole, Dorset, U.K., and the United States PharmacopoeiaPharmacopeia and National Formulary, U.
S. Pharmaceutical U.S. Pharmacopeial Convention, Inc. (SUPT.),(USPC), Rockville, MD.
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8.3 2-Propanol, minimum 99 % purity, for cleaning of analyzer parts in the sample chamber that may become contaminated with
spilled samples and other contaminants.
8.4 1,2,4-Trichlorobenzene, a high-purity liquid (minimum 99 % purity) with a certified chlorine concentration. Use the certified
chlorine concentration when calculating the exact concentrations of chlorine in calibration standards.
8.5 Quality-Control Samples, for use in establishing and monitoring the stability and precision of an analytical measurement
system (see Section 17). Use homogeneous materials, similar to samples of interest and available in sufficient quantity to be
analyzed regularly for a long period of time.
NOTE 2—Verification of system control through the use of QC samples and control charting is highly recommended.
NOTE 3—Suitable QC samples can be prepared by combining retains of typical samples.
8.6 Xylene, use a high purity p-xylene HPLC grade and account for its chlorine content when calculating the chlorine
concentration of the calibration standards.
8.7 Drift-Monitor Sample (optional), to determine and correct instrument drift over time (see 12.4, 13.2, and 14.2). Various forms
of stable chlorine-containing materials are suitable drift-correction samples, for example, liquid petroleum, solid, and pressed
powder. The count rate displayed by the monitor sample, in combination with a convenient count time (T), shall be sufficient to
give a relative standard deviation (RSD) of <1 % (see Appendix X1).
NOTE 4—Calibration standards may be used as drift-monitor samples.
NOTE 5—Because it is desirable to discard test specimens after each determination, a lower cost material is suggested for daily use. Any stable material
can be used for daily monitoring of drift.
NOTE 6—The effect of drift correction on the precision and bias of this test method has not been studied.
9. Hazards
9.1 Warning—WarningExposure—Exposure to excessive quantities of X-ray radiation is injurious to health. The operator needs
to take appropriate actions to avoid exposing any part of his/her body, not only to primary X-rays, but also to secondary or scattered
radiation that might be present. The X-ray spectrometer should be operated in accordance with the regulations governing the use
of ionizing radiation.
9.2 Consult current OSHA regulations, suppliers’ Safety Data Sheets and local regulations for all materials used in this test
method.
10. Sampling and Handling
10.1 Sample the material in accordance with Practice D3437.
10.2 For each sample, an unused piece of X-ray transparent film is required for the sample cell. Avoid touching the inside of the
sample cell, any portion of the film exposed to the liquid or the X-ray beam, and also avoid touching the instrument window. Oil
from fingerprints and wrinkles can generate errors in the analysis of chlorine. Therefore, make sure the film is taut and clean to
ensure reliable results. It is recommended to use canned air to ensure the film and sample cup is dust free prior to assembling
sample cell. Use calibration-check samples (see 8.2) to verify calibration integrity if the type and thickness of the window film is
changed. After the sample cell is filled, provide a vent above the sample to prevent bowing of the film by accumulating vapors.
When reusable sample cells are used, thoroughly clean and dry cells before each use. Disposable sample cells shall not be reused.
10.3 Because impurities and thickness variations can occur in commercially available transparent films and vary from lot to lot,
use calibration-check samples (see 8.2) to verify calibration integrity after starting each new batch of film.
11. Preparation of Apparatus
11.1 Analyzer Preparation—Ensure that the MWDXRF analyzer has been installed and put into operation in accordance with
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manufacturer’s instructions. Allow sufficient time for instrument electronics to stabilize. Perform any instrument checkout
procedures required. When possible, the instrument should be run continuously to maintain optimum stability.
11.1.1 Use the count time (T) recommended by the instrument manufacturer for the lowest chlorine concentration expected. The
typical time for each measurement is five or ten minutes.
11.1.2 Alternatively, determine T expected for a desired count precision by following the procedure in Appendix X1.
11.2 Minimizing Analyzer Contamination—Analyzer contamination may lead to falsely high measurement results. To minimize
analyzer contamination, perform the following steps at least once each day the analyzer is in use.
11.2.1 Clean the portion of the lid that is in contact with the top of the sample cell with 2-propanol. Additionally, clean the lid
after measurement of a sample containing greater than 50 mg/kg chlorine and prior to the measurement of sample containing less
than 1 mg/kg chlorine. Residue from higher concentration samples may contaminate subsequent low concentration measurements.
Wipe up any visible sample residue after sample measurement.
11.2.2 Clean the primary window with 2-propanol soaked foam tipped or cotton swab. Shake excess alcohol from swab prior to
using it for cleaning, as excess alcohol on the swab may leave a residue on the primary window when it dries. IIt is recommended
to use canned air to blow the window dry. For analyzers with disposable primary windows, change the window instead of cleaning
it.
11.2.3 Clean the sample basket with 2-propanol. Additionally, clean the sample basket any time the sample cell leaks in the
measurement chamber.
11.2.4 If the analyzer is equipped with a secondary window, change the film. It is recommended to use canned air to ensure the
film is dust free prior to reassembling the secondary window. Periodically inspect the secondary window and change if wrinkled,
dirty, torn, or if there is a sample cell leak in the measurement chamber. Additionally, change the secondary window after
measurement of a sample containing greater than 50 mg/kg chlorine prior to the measurement of samples containing less than 1
mg/kg chlorine. Residue vapors f
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