ASTM D7184-20

Standard Test Method for Ultra Low Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection

SIGNIFICANCE AND USE
5.1 This test method is useful to detect and quantify nitrogen-containing compounds at a concentration of 0.1 to 1.2 mg N/kg in light aromatic hydrocarbons used or produced in manufacturing process. These nitrogen-containing compounds are undesirable in finished aromatic products and may be used in setting specification for determining the total nitrogen content in aromatic hydrocarbons.  
5.2 This test method requires the use of reduced pressure at the detector. Loss of vacuum or pressure fluctuations impact the sensitivity of the detector and the ability to determine nitrogen concentrations less than 1 mg N/kg.
SCOPE
1.1 This test method covers the determination of total nitrogen in aromatic hydrocarbons, such as benzene, toluene, and xylene.  
1.2 This test method is applicable to samples with nitrogen concentrations up to 1.2 mg/kg. The Limit of Detection (LOD) is 0.04 mg/kg N and the Limit of Quantitation (LOQ) is 0.13 mg/kg N. For higher nitrogen concentrations refer to Test Method D4629. With careful analytical technique, this method can be used to successfully analyze concentrations below the current scope (see Appendix X1).
Note 1: LOD and LOQ were calculated using data in ASTM Research Report RR:D16-1044.  
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 statements, 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: 31-May-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 D7184-19 - Standard Test Method for Ultra Low Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection
• Effective Date: 01-Jun-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 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 D3437-11 - Standard Practice for Sampling and Handling Liquid Cyclic Products
• Effective Date: 01-Jan-2011
• Refers: ASTM D4629-10 - Standard Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection
• Effective Date: 01-Jul-2010
• Refers: ASTM D3437-10 - Standard Practice for Sampling and Handling Liquid Cyclic Products
• Effective Date: 01-Jun-2010
• Refers: ASTM D4629-09 - Standard Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection
• Effective Date: 15-Apr-2009
• 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 E29-08 - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 01-Oct-2008
• Refers: ASTM D4629-08 - Standard Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection
• Effective Date: 01-Jul-2008
• Refers: ASTM D3437-08 - Standard Practice for Sampling and Handling Liquid Cyclic Products
• Effective Date: 01-Jun-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 D4629-02(2007) - Standard Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection
• Effective Date: 01-May-2007
• Refers: ASTM E29-06b - Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
• Effective Date: 15-Nov-2006

Overview

ASTM D7184-20 is the international standard test method that specifies procedures for determining ultra low nitrogen content in aromatic hydrocarbons, including benzene, toluene, and xylene. Utilizing oxidative combustion combined with reduced pressure chemiluminescence detection, this method enables sensitive detection and quantification of nitrogen-containing compounds at concentrations ranging from 0.1 to 1.2 mg N/kg. The presence of nitrogen compounds in aromatic hydrocarbons is undesirable in finished products, making this standard essential for quality control and specification compliance in manufacturing processes.

Key Topics

• Analytical Range: Detects total nitrogen in light aromatic hydrocarbons with concentrations from 0.1 to 1.2 mg N/kg. The method's Limit of Detection (LOD) is 0.04 mg N/kg, and the Limit of Quantitation (LOQ) is 0.13 mg N/kg.
• Testing Methodology: Involves injecting a sample into a high-temperature furnace for oxidative combustion, where nitrogen compounds are converted to nitric oxide (NO). Chemiluminescence detection at reduced pressure increases sensitivity, enabling trace analysis.
• Interferences: High halogen content (above 10% by weight) and moisture can interfere with the test results. Sample and reagent purity, as well as proper sample handling, are vital to avoid contamination and ensure accurate analysis.
• Calibration and Quality Control: Emphasizes calibration using gravimetrically prepared standards and the importance of regular quality assurance and instrument validation according to established protocols.
• SI Units: All results are reported in SI units, ensuring international consistency and comparability.

Applications

• Aromatic Hydrocarbons Manufacturing: Used to screen and control nitrogen content in key process intermediates and finished products, including benzene, toluene, and xylene. Helps manufacturers meet product specifications and industry standards.
• Quality Assurance: Critical for setting and verifying specifications for total nitrogen content in light aromatic hydrocarbons, ensuring compliance with environmental and market requirements.
• Regulatory Compliance: Supports adherence to global regulatory standards, including environmental and safety regulations related to nitrogenous impurities in petrochemicals.
• Laboratory Testing: Ideal for laboratory environments requiring detection of trace levels of nitrogen. The standard's procedures support repeatable and reproducible results, vital for inter-laboratory studies.

Related Standards

• ASTM D4629: For measuring higher nitrogen concentrations in liquid hydrocarbons by syringe/inlet oxidative combustion and chemiluminescence detection.
• ASTM D3437: Practice for sampling and handling of liquid cyclic products.
• ASTM D6809: Guide for quality control and 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 interlaboratory studies to determine test method precision.

Practical Value

ASTM D7184-20 is vital for chemical producers, testing laboratories, and quality control personnel involved in the production and certification of aromatic hydrocarbons. By enabling the accurate detection of ultra low levels of nitrogen compounds, it ensures product purity, supports regulatory compliance, and protects end-use applications where even trace nitrogen can lead to product degradation or process complications. The standard underscores the importance of rigorous calibration, sample handling, and adherence to best laboratory practices-ensuring reliable, repeatable, and internationally recognized results.

Keywords: ASTM D7184-20, ultra low nitrogen detection, aromatic hydrocarbons, oxidative combustion, chemiluminescence detection, benzene, toluene, xylene, nitrogen analysis, quality control standards.

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: D7184 − 20
Standard Test Method for
Ultra Low Nitrogen in Aromatic Hydrocarbons by Oxidative
Combustion and Reduced Pressure Chemiluminescence
Detection
This standard is issued under the fixed designation D7184; 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
2.1 ASTM Standards:
1.1 This test method covers the determination of total
D3437 Practice for Sampling and Handling Liquid Cyclic
nitrogen in aromatic hydrocarbons, such as benzene, toluene,
Products
and xylene.
D4629 Test Method for Trace Nitrogen in Liquid Hydrocar-
1.2 This test method is applicable to samples with nitrogen
bons by Syringe/Inlet Oxidative Combustion and Chemi-
concentrations up to 1.2 mg/kg. The Limit of Detection (LOD)
luminescence Detection
is 0.04 mg/kg N and the Limit of Quantitation (LOQ) is 0.13
D6809 Guide for Quality Control and Quality Assurance
mg/kg N. For higher nitrogen concentrations refer to Test
Procedures for Aromatic Hydrocarbons and Related Ma-
Method D4629. With careful analytical technique, this method
terials
can be used to successfully analyze concentrations below the
E29 Practice for Using Significant Digits in Test Data to
current scope (see Appendix X1).
Determine Conformance with Specifications
NOTE 1—LOD and LOQ were calculated using data inASTM Research
E691 Practice for Conducting an Interlaboratory Study to
Report RR:D16-1044.
Determine the Precision of a Test Method
1.3 In determining the conformance of the test results using 2.2 Other Documents:
this method to applicable specifications; results shall be OSHA Regulations, 29 CFR paragraphs 1910. 1000 and
rounded off in accordance with the rounding-off method of 1910.1200
Practice E29.
3. Terminology
1.4 The values stated in SI units are to be regarded as
3.1 Definitions:
standard. No other units of measurement are included in this
3.1.1 oxidative pyrolysis, n—a process in which a sample
standard.
undergoes combustion in an oxygen rich environment at
1.5 This standard does not purport to address all of the
temperatures greater than 900°C.
safety concerns, if any associated with its use. It is the
3.1.2 pyrolytic decomposition, n—combusting a compound
responsibility of the user of this standard to establish appro-
to decompose it to carbon dioxide, water and elemental oxides.
priate safety, health, and environmental practices and deter-
3.1.3 reduced pressure chemiluminescence, n—a chemical
mine the applicability of regulatory limitations prior to use.
reaction at pressure less than 760 mm mercury (Hg) in which
For specific hazard statements, see Section 9.
light is emitted.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
4. Summary of Test Method
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- 4.1 A specimen is introduced into a carrier gas stream, at a
mendations issued by the World Trade Organization Technical controlled rate, and incorporated into a high temperature
Barriers to Trade (TBT) Committee. furnace (900 to 1150°C) where an excess of oxygen is added.
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 June 1, 2020. Published June 2020. Originally AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
approved in 2007. Last previous edition approved in 2019 as D7184 – 19. DOI: 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
10.1520/D7184-20. 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
D7184 − 20
Pyrolysis converts hydrocarbons in the specimen to carbon 7.7 Boat Inlet System (Optional)—If the instrument is
dioxide and water. Organic nitrogen and inorganic nitrogen equipped with a boat inlet system, care must be taken to ensure
compounds, present in the specimen, are converted to nitric the boat is sufficiently cooled between analyses to prevent the
oxide (NO). Nitric oxide reacts with ozone in the detector sample from vaporizing as it is injected into the boat. The
producing nitrogen dioxide molecules in an excited state. As sample should start vaporizing as it enters the furnace. It is
the excited nitrogen dioxide molecules relax to ground state, critical that the sample vaporize at a constant and reproducible
light is emitted.This light is detected by a photomultiplier tube rate.
or by a photodiode with the resulting signal proportional to the
7.8 Automatic Boat Drive System—If the instrument is
concentration of nitrogen in the sample. Operating the detector
equipped with a boat inlet system, the boat should be intro-
at a reduced pressure lowers the probability of the excited
duced into the furnace at a controlled rate.
nitrogen dioxide molecule colliding with other molecules
7.9 Membrane Dryer—Removes moisture of combustion
before it undergoes chemiluminescence. Thus, reduced pres-
before the detector.
sure provides improved sensitivity and lower noise.
8. Reagents
5. Significance and Use
8.1 Purity of Reagents—Reagent grade chemicals shall be
5.1 This test method is useful to detect and quantify
used in all tests. It is intended that all reagents shall conform to
nitrogen-containing compounds at a concentration of 0.1 to 1.2
the specifications of the Committee on Analytical Reagents of
mg N/kg in light aromatic hydrocarbons used or produced in
the American Chemical Society, where such specifications are
manufacturing process. These nitrogen-containing compounds
available, unless otherwise indicated. Other grades may be
are undesirable in finished aromatic products and may be used
used, provided it is first ascertained that the reagent is of
in setting specification for determining the total nitrogen
sufficiently high purity to permit its use without lessening the
content in aromatic hydrocarbons.
accuracy of the determination.
5.2 This test method requires the use of reduced pressure at
8.2 Inert Gas—Either argon (Ar) or helium (He) may be
the detector. Loss of vacuum or pressure fluctuations impact
used. The purity shall be no less than 99.99 mol %.
the sensitivity of the detector and the ability to determine
nitrogen concentrations less than 1 mg N/kg.
8.3 Oxygen Gas—The purity shall be no less than 99.99
mol %.
6. Interferences
8.4 Solvent—The solvent of choice should be capable of
6.1 Chlorides,bromides,andiodidescaninterfereifanyone
dissolving the nitrogen sample. The solvent of choice should
or all of these elements are present in a sample in concentra-
have a boiling point similar to the sample being analyzed. The
tions greater than 10 % by total weight of halogen in the
solvent should contain less than 0.05 mg N/L. The blank value
sample.
must be determined for each new bottle of solvent. Suggested
6.2 Moisture in the sample produced during the combustion possibilities include, but not limited to methanol, iso-octane
step can interfere if not removed prior to the gas entering the
and p-xylene.
detector cell.
NOTE 2—A quick screening can be conducted by injecting the solvent
and sample once or twice and comparing relative area counts.
7. Apparatus
8.5 Nitrogen Stock Solution, approximately 1000 mg N/L—
7.1 Pyrolysis Furnace—Afurnace capable of maintaining a
Prepare a stock solution by weighing, to the nearest 0.1 mg
temperaturesufficienttovolatilizeandpyrolysethesampleand
approximately 0.57 g of pyridine into a 100 ml volumetric
oxidize organically bound nitrogen to NO.The actual tempera-
flask. Dilute to the mark with solvent. Calculate the actual
ture should be recommended by the specific instrument manu-
concentration of nitrogen using Eq 1. This standard may also
facturer.
be purchased.
7.2 Quartz Pyrolysis Tube—Capable of withstanding 900 to
~Wt. of pyridine in grams! 3 ~.1771! 3 ~10 !
1200°C. mgN/L 5 (1)
100 ml of solvent
7.3 Chemiluminescence Detector—Capable of operation at
where:
reduced pressure (less than 760 mm mercury) and able to
% nitrogen in pyridine = 17.71
measure light emitted from the reaction between NO and
ozone.
8.6 Nitrogen Working Standard Solution—Calculatethecor-
rect concentration obtained from the nitrogen stock solution
7.4 Microliter Syringe—5 to 250 µL or as recommended by
prepared in 8.5 and prepare the working standards by diluting
instrument manufacturer.
7.5 Constant Rate Injector System—If the sample is to be
introduced into the pyrolysis furnace via syringe, use a
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
constant rate injector or a liquid introduction module or as
Standard-Grade Reference Materials, American Chemical Society, Washington,
recommended by instrument manufacturer. DC. For suggestions on the testing of reagents not listed by theAmerican Chemical
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
7.6 Liquid Auto-Sampler—Capable of injecting 5 to 250 µL
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
of sample or as recommended by instrument manufacturer. copeial Convention, Inc. (USPC), Rockville, MD.
D7184 − 20
the stock solution with the solvent. Prepare approximately 10.0 11.3 Adjust gas flows and pyrolysis temperatures to the
mg N/L standard by accurately pipeting 1.0 mL of the stock operating conditions as recommended by the instrument manu-
solution into a 100 ml volumetric flask and dilute to mark with facturer.
solvent. This Standard is further diluted to 0.05, 0.10, 0.5 and
11.4 The actual operation of injecting a sample will vary
1.0 mg N/L by accurately pipeting 0.5, 1.0, 5 and 10.0 mL of
depending upon the instrument manufacturer and type of inlet
standardintofourseparate100mLvolumetricflasksanddilute
system used (see 7.5 – 7.8).
to the mark with solvent. The working standards will be
approximately blank, 0.05, 0.1, 0.5, and 1.0 mg N/L. Calculate
12. Calibration and Standardization
the correct concentrations using the calculation:
12.1 Prepare the working calibration standards using the
mg N/L 5 mg N/L in working standard 3 ml pipeted / 100 ml (2)
~ ! ~ ! ~ !
stock solution as described in 8.5 and 8.6.
or
12.2 Before injecting a standard or blank, refer to the
mg N/Kg 5 mg N/L in working standard
~ !
procedures (Section 13), to ensure proper technique for either
3 ~ml pipeted!/~100 ml!*~Density of solution g/ml! (3)
the direct injection system or the boat inlet system.
Alternate volumes of solutions may be prepared so long as
12.3 A calibration based on the four gravimetrically pre-
the preparation meets the concentration specified.
pared standards works well within the limited scope of this
procedure. This type of calibration can be used to quantitate
NOTE 3—Working standards should be prepared on a regular basis
nitrogen at the 0.1 to 1.2 mg N/kg concentration range.
depending upon the frequency of use and age. The stock solution can be
retained, if refrigerated, for up to three months. Do not refrigerate stock
12.4 Run a calibration program for linear regression in
solutionifpreparedinbenzeneasthebenzenewillfreezeandcauseerratic
accordance with the instrument manufacturer’s recommenda-
results.
tions.The correlation coefficient should be a minimum of 0.99.
8.7 Cupric Oxide (CuO or Platinum (Pt)—May be used as
12.5 Inject each standard and blank at least 3 times.
an oxidation catalyst in the combustion tube, as recommended
by the instrument manufacturer.
NOTE 4—The calibration corrects for residual nitrogen content of the
solvent used to make the standards (often greater than 0.05 mg N/L) by
8.8 Quartz Wool—May be needed if recommended by the
generating the regression line as a standard addition to the solvent blank.
instrument manufacturer.
The slope generated is used to create a calibration line starting at the
origin, that is, zero signal for nitrogen.
9. Hazards
13. Procedure
9.1 Consult current OSHA regulations, chemical suppliers’
Safet
...

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: D7184 − 19 D7184 − 20
Standard Test Method for
Ultra Low Nitrogen in Aromatic Hydrocarbons by Oxidative
Combustion and Reduced Pressure Chemiluminescence
Detection
This standard is issued under the fixed designation D7184; 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 nitrogen in aromatic hydrocarbons, such as benzene, toluene, and xylene.
1.2 This test method is applicable forto samples containingwith nitrogen from 0.1 to 1.2 mg N/kg. concentrations up to 1.2
mg/kg. The Limit of Detection (LOD) is 0.04 mg/kg N and the Limit of Quantitation (LOQ) is 0.13 mg/kg N. For higher nitrogen
concentrations refer to Test Method D4629. With careful analytical technique, this method can be used to successfully analyze
concentrations below the current scope (see Appendix X1).
NOTE 1—LOD and LOQ were calculated using data in ASTM Research Report RR:D16-1044.
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 statements, 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
D4629 Test Method for Trace Nitrogen in Liquid Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence
Detection
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 Other Documents:
OSHA Regulations, 29 CFR paragraphs 1910. 1000 and 1910.1200
3. Terminology
3.1 Definitions:
3.1.1 oxidative pyrolysis, n—a process in which a sample undergoes combustion in an oxygen rich environment at temperatures
greater than 900°C.
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 D16.04 on Instrumental Analysis.
Current edition approved Nov. 1, 2019June 1, 2020. Published November 2019June 2020. Originally approved in 2007. Last previous edition approved in 2019 as
ɛ1
D7184 – 15 (2019)D7184 – 19. . DOI: 10.1520/D7184-19.10.1520/D7184-20.
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 U.S. Government Printing Office Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
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
D7184 − 20
3.1.2 pyrolytic decomposition, n—combusting a compound to decompose it to carbon dioxide, water and elemental oxides.
3.1.3 reduced pressure chemiluminescence, n—a chemical reaction at pressure less than 760 mm mercury (Hg) in which light
is emitted.
4. Summary of Test Method
4.1 A specimen is introduced into a carrier gas stream, at a controlled rate, and incorporated into a high temperature furnace
(900 to 1150°C) where an excess of oxygen is added. Pyrolysis converts hydrocarbons in the specimen to carbon dioxide and water.
Organic nitrogen and inorganic nitrogen compounds, present in the specimen, are converted to nitric oxide (NO). Nitric oxide
reacts with ozone in the detector producing nitrogen dioxide molecules in an excited state. As the excited nitrogen dioxide
molecules relax to ground state, light is emitted. This light is detected by a photomultiplier tube or by a photodiode with the
resulting signal proportional to the concentration of nitrogen in the sample. Operating the detector at a reduced pressure lowers
the probability of the excited nitrogen dioxide molecule colliding with other molecules before it undergoes chemiluminescence.
Thus, reduced pressure provides improved sensitivity and lower noise.
5. Significance and Use
5.1 This test method is useful to detect and quantify nitrogen-containing compounds at a concentration of 0.1 to 1.2 mg N/kg
in light aromatic hydrocarbons used or produced in manufacturing process. These nitrogen-containing compounds are undesirable
in finished aromatic products and may be used in setting specification for determining the total nitrogen content in aromatic
hydrocarbons.
5.2 This test method requires the use of reduced pressure at the detector. Loss of vacuum or pressure fluctuations impact the
sensitivity of the detector and the ability to determine nitrogen concentrations less than 1 mg N/kg.
6. Interferences
6.1 Chlorides, bromides, and iodides can interfere if any one or all of these elements are present in a sample in concentrations
greater than 10 % by total weight of halogen in the sample.
6.2 Moisture in the sample produced during the combustion step can interfere if not removed prior to the gas entering the
detector cell.
7. Apparatus
7.1 Pyrolysis Furnace—A furnace capable of maintaining a temperature sufficient to volatilize and pyrolyse the sample and
oxidize organically bound nitrogen to NO. The actual temperature should be recommended by the specific instrument
manufacturer.
7.2 Quartz Pyrolysis Tube—Capable of withstanding 900 to 1200°C.
7.3 Chemiluminescence Detector—Capable of operation at reduced pressure (less than 760 mm mercury) and able to measure
light emitted from the reaction between NO and ozone.
7.4 Microliter Syringe—5 to 250 μL or as recommended by instrument manufacturer.
7.5 Constant Rate Injector System—If the sample is to be introduced into the pyrolysis furnace via syringe, use a constant rate
injector or a liquid introduction module or as recommended by instrument manufacturer.
7.6 Liquid Auto-Sampler—Capable of injecting 5 to 250 μL of sample or as recommended by instrument manufacturer.
7.7 Boat Inlet System (Optional)—If the instrument is equipped with a boat inlet system, care must be taken to ensure the boat
is sufficiently cooled between analyses to prevent the sample from vaporizing as it is injected into the boat. The sample should start
vaporizing as it enters the furnace. It is critical that the sample vaporize at a constant and reproducible rate.
7.8 Automatic Boat Drive System—If the instrument is equipped with a boat inlet system, the boat should be introduced into
the furnace at a controlled rate.
7.9 Membrane Dryer—Removes moisture of combustion before the detector.
8. Reagents
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. 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,
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.
D7184 − 20
unless otherwise indicated. 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 Inert Gas—Either argon (Ar) or helium (He) may be used. The purity shall be no less than 99.99 mol %.
8.3 Oxygen Gas—The purity shall be no less than 99.99 mol %.
8.4 Solvent—The solvent of choice should be capable of dissolving the nitrogen sample. The solvent of choice should have a
boiling point similar to the sample being analyzed. The solvent should contain less than 0.05 mg N/L. The blank value must be
determined for each new bottle of solvent. Suggested possibilities include, but not limited to methanol, iso-octane and p-xylene.
NOTE 2—A quick screening can be conducted by injecting the solvent and sample once or twice and comparing relative area counts.
8.5 Nitrogen Stock Solution, approximately 1000 mg N/L—Prepare a stock solution by weighing, to the nearest 0.1 mg
approximately 0.57 g of pyridine into a 100 ml volumetric flask. Dilute to the mark with solvent. Calculate the actual concentration
of nitrogen using Eq 1. This standard may also be purchased.
Wt. of pyridine in grams 3 .1771 3 10
~ ! ~ ! ~ !
mg N/L5 (1)
100 ml of solvent
where:
% nitrogen in pyridine = 17.71
8.6 Nitrogen Working Standard Solution—Calculate the correct concentration obtained from the nitrogen stock solution
prepared in 8.5 and prepare the working standards by diluting the stock solution with the solvent. Prepare approximately 10.0 mg
N/L standard by accurately pipeting 1.0 mL of the stock solution into a 100 ml volumetric flask and dilute to mark with solvent.
This Standard is further diluted to 0.05, 0.10, 0.5 and 1.0 mg N/L by accurately pipeting 0.5, 1.0, 5 and 10.0 mL of standard into
four separate 100 mL volumetric flasks and dilute to the mark with solvent. The working standards will be approximately blank,
0.05, 0.1, 0.5, and 1.0 mg N/L. Calculate the correct concentrations using the calculation:
mg N/L 5 mg N/L in working standard 3 ml pipeted / 100 ml (2)
~ ! ~ ! ~ !
or
mg N/Kg 5 ~mg N/L in working standard! 3~ml pipeted!/~100 ml!*~Density of solution g/ml! (3)
Alternate volumes of solutions may be prepared so long as the preparation meets the concentration specified.
NOTE 3—Working standards should be prepared on a regular basis depending upon the frequency of use and age. The stock solution can be retained,
if refrigerated, for up to three months. Do not refrigerate stock solution if prepared in benzene as the benzene will freeze and cause erratic results.
8.7 Cupric Oxide (CuO or Platinum (Pt)—May be used as an oxidation catalyst in the combustion tube, as recommended by
the instrument manufacturer.
8.8 Quartz Wool—May be needed if recommended by the instrument manufacturer.
9. Hazards
9.1 Consult current OSHA regulations, chemical suppliers’ Safety Data Sheets, and local regulations for all material used in this
test method.
9.2 High temperature is employed in this test method. Extreme care should be exercised when using flammable materials near
the pyrolysis furnace.
9.3 Ozone can be hazardous so use of a good vented room is necessary.
10. Sample Handling
10.1 Collect the sample in accordance with Practice D3437.
10.2 To preserve sample integrity and prevent the loss of volatile components, which may be in some samples, do not expose
samples to the atmosphere any longer than necessary. Analyze specimen as soon as possible after transferring from the sample
container to prevent loss of nitrogen or contamination.
10.3 Since this procedure is intended for trace level analysis, care must be taken to ensure that the sample container, and
working standards containers are clean and do not contaminate the sample.
11. Instrument Assembly and Preparation
11.1 Setup the instrument in accordance with the instrument manufacturer’s instructions.
11.2 Set instrument parameters in accordance with instrument manufacturer’s recommendations.
11.3 Adjust gas flows and pyrolysis temperatures to the operating conditions as recommended by the instrument manufacturer.
D7184 − 20
11.4 The actual operation of injecting a sample will vary depending upon the instrument man
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