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Designation: D 6069 – 96
Standard Test Method for
Trace Nitrogen in Aromatic Hydrocarbons by Oxidative
Combustion and Reduced Pressure Chemiluminescence
Detection1
This standard is issued under the fixed designation D 6069; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of total
nitrogen (organic and inorganic) in aromatic hydrocarbons,
their derivatives and related chemicals.
1.2 This test method is applicable for samples containing
nitrogen from 0.2 to 2 mgN/kg. For higher nitrogen concentrations
refer to Test Method D 4629.
1.2.1 The detector response of this technique within the
specified scope of this test method is linear with nitrogen
concentration.
1.3 The following applies to all specified limits in this test
method: for purposes of determining conformance with this
test method, an observed value or a calculated value shall be
rounded off “to the nearest unit” in the last right-hand digit
used in expressing the specification limit, in accordance with
the rounding-off method of Practice E 29.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate
safety and health practices and determine the applicability
of regulatory limitations prior to use. For specific hazard
statements, see Section 9.
2. Referenced Documents
2.1 ASTM Standards:
D 1555 Test Method for Calculation of Volume and Weight
of Industrial Aromatic Hydrocarbons2
D 3437 Practice for Sampling and Handling Liquid Cyclic
Products2
D 4629 Test Method for Organically Bound Trace Nitrogen
in Liquid Petroleum Hydrocarbons By Syringe/Inlet Oxidative
Combustion and Chemiluminescence Detection3
E 29 Practice for Using Significant Digits in Test Data to
Determine Conformance with Specifications4
E 691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method4
2.2 Other Documents:
OSHA Regulations, 29 CFR, paragraphs 1910.1000 and
1910.12005
3. Terminology
3.1 Definitions:
3.1.1 reduced pressure chemiluminescence—a chemical reaction
at pressure less than 760 mm mercury (Hg) in which
light is emitted.
3.1.2 oxidative pyrolysis—a process in which a sample
under goes combustion in an oxygen rich environment at
temperatures greater than of 650°C.
3.1.2.1 Discussion—Organic compounds pyrolytically decompose
to carbon dioxide, water and elemental oxides.
4. Summary of Test Method
4.1 A specimen is introduced into a gas stream, at a
controlled rate, and carried into a high temperature furnace
(>900°C) where an excess of oxygen is added. Pyrolysis
converts organic material 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 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 molecules
colliding with other molecules before it under goes
chemiluminescence. Thus, reduced pressure provides improved
sensitivity and lower noise.
5. Significance and Use
5.1 This method has been prepared to detect and quantitate
nitrogen-containing compounds such as N-formylmorpholine
(4-formylmorpholine, Chemical Abstract Service numbers
(CAS) No. 250-37-6) or 1-methyl-2-pyrrolidinone (NMP)
(CAS) No. 872-50-42 at a concentration of 1.0 mgN/kg or less
in aromatic hydrocarbons used or produced in manufacturing
1 This test method is under the jurisdiction of ASTM Committee D-16 on
Aromatic Hydrocarbons and Related Chemicals and is the direct responsibility of
Subcommittee D16.0E on Instrumental Analysis.
Current edition approved Dec. 10, 1996. Published February 1997.
2 Annual Book of ASTM Standards, Vol 06.04.
3 Annual Book of ASTM Standards, Vol 05.02.
4 Annual Book of ASTM Standards, Vol 14.02.
5 Available from the Superintendent of Documents, U.S. Government Printing
Office, Washington, DC 20402.
1
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
processes. These nitrogen-containing compounds are undesirable
in the finished aromatic products and may be the result of
the aromatic extraction process. This test method may be used
in setting specifications for determining the total nitrogen
content in aromatic hydrocarbons.
NOTE 1—Virtually all organic and inorganic nitrogen compounds will
be detected by this technique.
5.2 This technique will not detect diatomic nitrogen and it
will produce an attenuated response when analyzing compounds
(that is, s-triazine and azo compounds, etc.) that form
nitrogen gas (N2) when decomposed.
5.3 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/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 produced during the combustion step can
interfere if not removed prior to the detector cell.
7. Apparatus
7.1 Pyrolysis Furnace—A furnace capable of maintaining a
temperature sufficient to volatilize and pyrolyze the sample and
oxidize organically bound nitrogen to NO. The actual temperature(
s) should be recommended by the specific instrument
manufacturers.
7.2 Quartz Pyrolysis Tube—Capable of withstanding 900 to
1200°C.
7.2.1 Quartz Pyrolysis Tube—The suggested maximum
temperature for a quartz pyrolysis tube is 1200°C. Samples
containing alkali-metals (elements from the Periodic Group IA
(that is, Na, K, etc.)) or alkaline earths (elements from the
Periodic Group IIA (that is, Ca, Mg, etc.)) will cause quartz to
devitrify (that is, become milky white and brittle).
7.3 Chemiluminescent Detector—Capable of operation at
reduced pressures (less than 760 mm mercury) and able to
measure light emitted from the reaction between NO and
ozone.
7.4 Microlitre Syringe—Capable of delivering from 5 to 50
μL of sample. Check with the instrument manufacturer for
recommendations for specific sample needs.
7.5 Constant Rate Injector System (Optional)—If the
sample is to be introduced into the pyrolysis furnace via
syringe, a constant rate injector should be used.
7.6 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. This type of inlet system offers advantage when the
sample is viscous or contains heavy components not volatile at
temperatures of approximately 300°C, or for samples that
contain polymers or high concentrations of salts that could
result in plugging of the syringe needle.
7.7 Automatic Boat Drive System (Optional)—If the instrument
is equipped with a boat inlet system, a device for driving
the boat in to the furnace at a controlled and repeatable rate
may improve data repeatability and reproducibility.
7.8 Oxidation Catalyst (Optional)—Catalyst (that is, cupric
oxide (CuO) or Platinum (Pt)) may be packed into the pyrolysis
tube to aid in oxidation efficiencies (see manufacturer’s recommendations).
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,6 where such specifications are
available, 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 should be no less than 99.99 mol %.
8.3 Oxygen Gas—The purity should be no less than 99.99
mol %.
8.4 Solvent—The solvent chosen should be capable of
dissolving the nitrogen containing compound used to prepare
the standard and if necessary the samples. The solvent of
choice should have a boiling point similar to the samples being
analyzed and it should contain less nitrogen than the lowest
sample to be analyzed. Suggested possibilities include, but are
not limited to: toluene, methanol, tetrahydrofuran, iso-octane.
NOTE 2—A quick screening can be conducted by injecting the solvent
and sample once or twice and comparing relative area counts.
8.4.1 Solvent—Toluene, relative density at 60°F/60°F
0.8718 (see Test Method D 1555).
8.5 Nitrogen Stock Solution, 1000 μg N/mL—Prepare a
stock solution by accurately weighing, to the nearest 0.1 mg,
approximately 707.7 mg of 1-methyl-2-pyrrolidinone (NMP)
(CAS No. 872-50-4) into a 100-mL volumetric flask. Fill to
volume with solvent as follows:
μg N/mL 5
exact weight of NMP ~mg! 3 14.0 3 1000 ~μg/mg!
100 mL 3 99.1
(1)
where:
14.0 5 the atomic weight of nitrogen, and
99.1 5 the molecular weight of NMP.
8.6 Nitrogen Working Standard Solutions, 1.0 and 2.0 μg
N/mL—The working standards are prepared by dilution of the
stock solution with the solvent. Prepare a 100-μg N/mL
standard by accurately pipetting 10 mL of stock solution into a
100-mL volumetric flask and diluting to volume with solvent.
This standard is further diluted to 1.0 and 2.0-μg N/mL by
accurately pipetting 1 mL of the 100 μg-N/mL standard into a
6 Reagent Chemicals, American Chemical Society Specifications, 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.
D 6069
2
clean 100-mL volumetric flask and pipetting 2 mL of the
100-μg N/mL standard into a different clean 100-mL volumetric
flask and diluting each to volume with solvent.
NOTE 3—Working standards should be prepared on a regular basis
depending upon the frequency of use and age. Typically, standards have a
useful life of about 3 months.
8.7 Cupric Oxide (CuO) or Platinum (Pt)—May be used as
an oxidation catalyst, 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, suppliers’ Material
Safety Data Sheets, and local regulations for all materials used
in this test method.
9.2 High temperature is employed in this test method.
Warning—Extreme care should be exercised when using
flammable materials near the pyrolysis furnace.
10. Sample Handling
10.1 Collect the samples in accordance with Practice
D 3437.
10.2 To preserve sample integrity (consistency) and prevent
the loss of volatile components, which may be in some
samples, do not uncover samples 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 contamination,
care must be taken to ensure the containers used for
the sample, the specimen, and the working standard do not alter
the sample results.
11. Instrument Assembly and Preparation
11.1 Install the instrument in accordance with manufacturer’s
instructions. See Appendix X1 for typical set-up parameters.
11.2 Adjust gas flows and pyrolysis temperature(s) to the
operating conditions as recommended by the manufacturer.
11.3 The actual operation of injecting a sample will vary
depending upon the instrument manufacturer and the type of
inlet system used (see 7.5-7.8).
12. Calibration and Standardization
12.1 Prepare the working calibration standards using the
stock solution as described in 8.5 and 8.6.
12.1.1 Before injecting a standard or blank, refer to procedures
(see Section 13, Procedure), to ensure proper technique
for either the direct injection system or the boat inlet system.
12.2 A calibration based on the difference between two
gravimetrically prepared standards works well within the
limited scope of this procedure. This type of calibration can be
used to quantitate nitrogen at the 1.0 ppm (wt/wt) concentration
or to determine pass/fail compliance. Two standards are
prepared with concentrations that differ by the target specification.
Thus, for a 1.0 ppm nitrogen (wt/wt) maximum
specification, prepare two standards that differ in concentration
by 1.0 ppm (that is, 2.0 μg-N/mL and a 1.0 μg-N/mL standard).
12.2.1 Each standard should be injected in triplicate and the
integrator counts averaged and recorded.
13. Procedure
13.1 Sample sizes from 5 to 50 μL are acceptable. Although,
at the concentration range from 0.2 to 2 μg N/mL, it is
recommended that the same size sample be used for all
standards and samples analyses.
NOTE 4—When an organic sample is injected into the pyrolysis furnace
a pressure wave is formed. The initial flash vaporization forms a positive
pressure pulse, thus decreasing detector sensitivity. After pyrolysis of the
organic material in the high-temperature furnace a reduced pressure pulse
is formed, resulting in increased detector sensitivity. Thus, maintaining the
same sample size for all injections (that is, samples and standards) will
improve repeatability and reproducibility. As mentioned in 8.4, Solvent,
using a solvent with a boiling point similar to that of the sample being
analyzed is generally recommended.
13.1.1 Always flush the syringe several times with the
material to be injected. To prevent contamination do not return
the first couple of flushes back into the specimen bottle.
13.1.2 If the instrument is equipped with a pyrolysis tube for
direct syringe injection, see 13.2. If the instrument is equipped
with a boat inlet system, see 13.3.
13.2 Fill syringe to approximately 1.5 times the volume to
be injected (that is, to inject 10 μL, fill a 25-μL syringe with 15
to 20 μL of sample or standard), taking care not to pull air
bubbles into the syringe with the sample. With the syringe
needle pointed up, push the plunger in to the desired volume,
tap the last drop off the needle point, and pull the plunger back
until air can be seen in the syringe barrel.
NOTE 5—The inherent accuracy of this technique is dependent upon the
ability of the analyst to repeatability inject the same volume for each
injection. Air bubbles lodged between the syringe plunger and the
specimen will result in variable specimen volumes. If bubbles persist, try
cleaning the syringe with a different solvent or try inserting the needle into
a septum and gently putting pressure on the syringe plunger (this may
cause persistent bubbles to break free).
NOTE 6—If the detector response continuously increases or decreases,
this is indicative of contamination. If this occurs, continue injecting the
specimen until the detector signal shows a typical variance.
13.2.1 Insert the syringe needle through the inlet septum as
far as it will go (the syringe barrel should be touching the
septum). Allow the residual sample in the needle to burn-off.
When the instrument returns to a stable baseline, zero or clear
the detector display and inject the specimen or standard at a
constant rate of 0.5 to 1.0 μL/s.
13.2.2 If an autosampler is used the detector will be
automatically zeroed prior to injection.
13.2.3 Repeat 13.2 analyzing each standard and sample in
triplicate. Average the three results for each standard or sample
and record the results.
13.3 With the boat inlet system, a specimen is injected into
a cool boat and the boat carried into the pyrolysis furnace.
Before analyzing standards or samples introduce the boat into
the furnace to burn-off any possible contamination.
13.3.1 Fill the syringe as described in 13.2. Inject the
standard or specimen into the cooled boat. Move the boat
containing the specimen into the furnace at a controlled and
repeatable rate.
D 6069
3
NOTE 7—The boat may be stopped at the furnace inlet to permit
evaporation, if a controlled combustion is necessary. Although, if the boat
is stopped, it must then be stopped at the same place and for the same
length of time for all analyses (see Note 4, Note 5, and Note 6).
13.3.2 Repeat 13.3 analyzing each sample, or standard in
triplicate. Average the three results for each sample and record
the results.
14. Calculation
14.1 Calculate the concentration of nitrogen as follows:
Nitrogen, mg/kg 5
Isx 3 ~Cstd2 2 Cstd1! 3 Vstd
~Istd2 2 Istd1! 3 Vsx 3 Dsx
(2)
where:
Isx 5 detector response of sample, integration counts,
Istd2 5 highest standard’s average detector response, integration
counts,
Istd1 5 lowest standard’s average detector response, integration
counts,
Cstd2 5 concentration of higher standard, μg N/mL,
Cstd1 5 concentration of lower standard, μg N/mL,
Dsx 5 density of the sample, g/mL,
Vsx 5 volume of sample injected, μL, and
Vstd 5 volume of standard solution injected, μL.
15. Precision and Bias
15.1 Precision—The following criteria7, conducted under
the guidelines of Practice E 691, should be used to judge the
acceptability (95 % probability) of the results obtained by this
test method. The criteria were derived from a interlaboratory
study between ten laboratories. Standards and samples were
analyzed in duplicate on the same day by a single operator.
Each analysis represented triplicate injections.
15.1.1 Repeatability—Results within laboratory results by
the same operator with the same equipment over the shortest
practicable period of time should not be considered suspect
unless they differ by more than the amount shown in Table 1.
15.1.2 Reproducibility—Results submitted by two laboratories
should not be considered suspect unless they differ by
more than the amount shown in Table 1.
15.2 Bias—Systematic error that contributes to a difference
between the mean and an accepted reference value. Since all
organic solvents can contain nitrogen, an absolute statement of
bias could not be determined from this study. Although, an
estimate of bias was determined by spiking a single solvent
(xylene) with three different concentrations of nitrogen. These
three spiked samples were then analyzed as unknowns in the
interlaboratory study (see Table 2).
16. Keywords
16.1 chemiluminescence; nitrogen
7 Supporting data are available from ASTM Headquarters. Request RR:D
16–1024.
TABLE 1 Repeatability and ReproducibilityA
Nitrogen Concentration,
mg/kg
Repeatability Reproducibility
0.32 0.09 0.25
0.60 0.15 0.26
0.88 0.19 0.34
A Repeatability and Reproducibility determined at the 95 % confidence level.
TABLE 2 Estimated Bias
Solvent
Nitrogen Spike,
mg N/kg
Average of 10
Laboratories
Nitrogen Results
Based on the ILS,
mg N/kg
Absolute
Difference
Xylene 0.32 0.32 0.00
Xylene 0.60 0.60 0.00
Xylene 0.88 0.87 0.01
D 6069
4
APPENDIX
(Nonmandatory Information)
X1. TYPICAL SET-UP CONDITIONS
X1.1 Table X1.1 illustrates two instrument’s parameters
and settings.
TABLE X1.1 Typical Set-Up ConditionsA,B
Instrument 1 Parameters Instrument 1 Settings
Syringe Drive Rate for Direct
Injection
(700–750) 1 μL/second
Boat Drive Rate for Boat Inlet (700–750) 140–160 mm/min
Furnace Temperature 1050 6 25°C
Furnace Oxygen Flowmeter Setting (3.8–4.1) 450–500 cc/min
Inlet Oxygen Flowmeter Setting (0.4–0.8) 10–30 cc/min
Inlet Carrier Flowmeter Setting (3.4–3.6) 130–160 cc/min
Ozone Oxygen Flowmeter Setting (1.5–1.7) 35–45 cc/min
Pyro-tube Back Pressure 1–2.5 psi
Gain High
Attenuation 50
Sample Size 20 μL
Instrument 2 Parameters Instrument 2 Settings
Automatic Boat Control 1 Fuc FWD 140 Speed 10 Time 30
2 Fuc FWD 285 Speed 05 Time 30
5 Fuc Time 30
6 Fuc Time 90
AFuc Time 60
Furnace Temperatures
Inlet 600°C
Catalyst 950°C
Gas Flow Setting
Main Oxygen 400 cc/min
Inlet Oxygen 0.4 L/min
Inlet Argon 0.4 L/min
Range Low
Attenuation 2
Sample Size 20 μL
AThe sole source of supply of the apparatus for Instrument 1, Antek Model 7000 known to the committee at this time is Antek Instruments, Inc., Houston, TX. If you are
aware of alternative suppliers, please provide this information to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible
technical committee1, “which you may attend.”
BThe sole source of supply of the apparatus for Instrument 2, Mitsubishi Model TN-10 known to the committee at this time is COSA Instrument Corp., Norwood, NJ. If
you are aware of alternative suppliers, please provide this information to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the
responsible technical committee1, “which you may attend.”
D 6069
5
The American Society for Testing and Materials takes no position respecting the validity of any patent rights asserted in connection
with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such
patent rights, and the risk of infringement of such rights, are entirely their own responsibility.
This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and
if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards
and should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible
technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make your
views known to the ASTM Committee on Standards, 100 Barr Harbor Drive, West Conshohocken, PA 19428.
D 6069
6
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