ASTM D2268-93(2017)

Standard Test Method for Analysis of High-Purity <emph type="ital">n</emph>-Heptane and <emph type="ital">Iso</emph>octane by Capillary Gas Chromatography

SIGNIFICANCE AND USE
3.1 This test method is used for specification analysis of high-purity n-heptane and  isooctane, which are used as ASTM Knock Test Reference Fuels. Hydrocarbon impurities or contaminants, which can adversely affect the octane number of these fuels, are precisely determined by this method.
SCOPE
1.1 This test method covers and provides for the analysis of high-purity (greater than 99.5 % by volume) n-heptane and isooctane (2,2,4-trimethylpentane), which are used as primary reference standards in determining the octane number of a fuel. Individual compounds present in concentrations of less than 0.01 % can be detected. Columns specified by this test method may not allow separation of all impurities in reference fuels.  
1.2 The values stated in SI units are to be regarded as the standard.  
1.2.1 Exception—The values given in parentheses are for information only.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 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: Historical
• Publication Date: 30-Sep-2017
• ICS: 71.080.10 - Aliphatic hydrocarbons
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.04.0L - Gas Chromatography Methods

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D2268 − 93 (Reapproved 2017)
Standard Test Method for
Analysis of High-Purity n-Heptane and Isooctane by
Capillary Gas Chromatography
This standard is issued under the fixed designation D2268; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope sponse from each impurity is then compared with that of a
known quantity of an internal standard. After determining the
1.1 This test method covers and provides for the analysis of
total impurity concentration, the n-heptane, or isooctane purity
high-purity (greater than 99.5 % by volume) n-heptane and
is obtained by difference.
isooctane (2,2,4-trimethylpentane), which are used as primary
reference standards in determining the octane number of a fuel.
3. Significance and Use
Individual compounds present in concentrations of less than
0.01 % can be detected. Columns specified by this test method 3.1 This test method is used for specification analysis of
may not allow separation of all impurities in reference fuels.
high-purity n-heptane and isooctane, which are used asASTM
Knock Test Reference Fuels. Hydrocarbon impurities or
1.2 The values stated in SI units are to be regarded as the
contaminants, which can adversely affect the octane number of
standard.
these fuels, are precisely determined by this method.
1.2.1 Exception—The values given in parentheses are for
information only.
4. Apparatus
1.3 This standard does not purport to address all of the
4.1 Chromatograph—Gas chromatograph should be
safety concerns, if any, associated with its use. It is the
equipped with a split-stream inlet device for introducing
responsibility of the user of this standard to establish appro-
minute quantities of sample without fractionation, a capillary
priate safety, health, and environmental practices and deter-
column, and a hydrogen flame ionization detector. An elec-
mine the applicability of regulatory limitations prior to use.
trometertoamplifythelowoutputsignalofthehydrogenflame
1.4 This international standard was developed in accor-
ionization detector, and a strip-chart recorder for recording the
dance with internationally recognized principles on standard-
detector signal are needed. The time constant of neither the
ization established in the Decision on Principles for the
electrometernortherecordershouldexceed1 s.Aballanddisk
Development of International Standards, Guides and Recom-
integrator or electronic integrator for peak area measurements
mendations issued by the World Trade Organization Technical
should be used. The detection system must have sufficient
Barriers to Trade (TBT) Committee.
sensitivity to produce a recorder deflection for cyclohexane of
2. Summary of Test Method
at least 8 divisions on a standard 0–100 scale chart using
0.10 % by volume of cyclohexane in n-heptane as defined in
2.1 The sample is injected into a capillary gas chromato-
7.1.
graphic column consisting of at least 61 m (200 ft) of stainless
steel tubing (0.25 mm (0.010 in.) inside diameter), the inner
4.2 Microsyringe—A microsyringe is needed for injecting
walls of which are coated with a thin film of stationary liquid. the sample into the split-stream inlet device.
An inert gas transports the sample through the column, in
4.3 Volumetric Pipet, 0.1 mL capacity.
which it is partitioned into its individual components. As each
4.4 Analytical Balance, 200 g capacity.
component is eluted from the column, it is detected with a
hydrogen flame ionization detector and recorded on a conven-
5. Reagents and Materials
tional strip-chart recording potentiometer. The detector re-
5.1 Carrier Gas—Argon, Nitrogen, or Helium; 99.99 % or
greater purity. (Warning—Compressed gases under high pres-
This test method is under the jurisdiction of ASTM Committee D02 on
sure.)
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.04.0L on Gas Chromatography Methods.
5.2 Fuel Gas—Hydrogen; 99.99 % or greater purity.
Current edition approved Oct. 1, 2017. Published November 2017. Originally
(Warning—Compressed gas under high pressure. Extremely
approved in 1964. Last previous edition approved in 2013 as D2268 – 93 (2013).
DOI: 10.1520/D2268-93R17. flammable gas.)
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2268 − 93 (2017)
5.3 Oxidant Gas—Air; 99.99 % or greater purity.
(Warning—Compressed gases under high pressure.)
5.4 Cyclohexane—At least 99 mol % pure, to be used as
internalstandard.(Warning—Flammableliquidandharmfulif
ingested or inhaled.)
5.5 n-Pentane—Commercial grade. (Warning—Volatile
and flammable liquid, and harmful if ingested or inhaled.)
5.6 Isooctane (2,2,4-trimethylpentane)—(Warning—
Flammable liquid and harmful if ingested or inhaled.)
FIG. 1 Column Resolution (R).
5.7 Squalane—Liquid phase for gas chromatographic col-
umns.
Resolution (R), using the above equation, must exceed a
5.8 Tubing—Type 316, 321, or 347 stainless steel; 0.25 mm
value of 10.
(0.010 in.) inside diameter.
7. Sample Preparation
6. Preparation of Resolving Column
7.1 Place 20 mL to 30 mL of the reference fuel (n-heptane
NOTE 1—There are many different procedures for coating capillary
columns.Asuitable procedure is given in 6.1 through 6.3. Other columns or isooctane) into a 100 mL volumetric flask which has been
may be used provided they meet resolution and repeatability requirements
previously weighed.
of the method.
7.2 Weigh the sample. Using a 0.10 mL volumetric pipet,
6.1 Connect a 229 mm (9 in.) section of stainless steel
add 0.10 mL of the internal standard cyclohexane (99 mol %,
tubing 6.4 mm ( ⁄4 in.) outside diameter, total volume of
min) and reweigh. Dilute to the mark with the n-heptane or
approximately 5 mL) to a high-pressure cylinder of argon,
isooctane sample and weigh. Use a 200 g analytical balance
helium, or nitrogen through a pressure regulator. Connect at
accurate to 60.0002 g. From these weights (masses) and the
least 61 m (200 ft) of Type 316, 321, or 347 stainless steel
relative density (specific gravities) of cyclohexane and
tubing (0.25 mm (0.010 in.) inside diameter) to the 229 mm
n-heptane or isooctane, calculate the volume percent of the
section of 64 mm tubing which is to be used as a reservoir for
cyclohexane internal standard to the nearest 0.001 volume
the coating solution. The capillary column is generally coiled
percent. (Relative density (specific gravity) of cyclohexane at
on a suitable mandrel before coating. To the other end of the
20 °C = 0.7786; n-heptane = 0.6838, and 2,2,4-trimethylpen-
capillary column, connect an additional 30 m to 9 m to 12 m
tane = 0.6919.)
(40 ft) of capillary tubing through a 1.6 mm ( ⁄16 in.) Swagelok
Cyclohexane, volume% 5 wt cyclohexane/rel dens cyclohexane (2)
union.
6.2 Clean the tubing by passing 25 mL to 30 mL (5 to 6 ÷ wt reference fuel/rel dens reference fuel 3100
~ !
reservoir volumes) of n-pentane through the tubing with about
8. Procedure
1.7 MPa to 2.1 MPa (250 psig to 300 psig gage) of inert gas.
After the column has been cleaned, disconnect the upstream
8.1 Adjust the operating variables to optimum conditions.
end of the reservoir tube and allow the pressure in the tubing
Temperatures should be as follows: Injection port and splitter
to return to atmospheric.
150 °Cto250 °C,columnatoptimumtemperatureanddetector
greater than 100 °C. Adjust the excess gas flow through the
6.3 Prepare a solution containing 6 volume percent of
splitter to provide a proper sample size to the column.
squalane in n-pentane. Fill the reservoir tube with the coating
solution and promptly connect to the gas cylinder. Pass the
8.2 Usingthemicrosyringe,injectsufficientsamplecontain-
coating solution through the column at 500 psig (3.5 MPa
ing the internal standard. Both the sample volume and the split
gage) until the solution begins issuing from the end of the
ratio must be considered in choosing the c
...

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: D2268 − 93 (Reapproved 2013) D2268 − 93 (Reapproved 2017)
Standard Test Method for
Analysis of High-Purity n-Heptane and Isooctane by
Capillary Gas Chromatography
This standard is issued under the fixed designation D2268; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers and provides for the analysis of high-purity (greater than 99.5 % by volume) n-heptane and
isooctane (2,2,4-trimethylpentane), which are used as primary reference standards in determining the octane number of a fuel.
Individual compounds present in concentrations of less than 0.01 % can be detected. Columns specified by this test method may
not allow separation of all impurities in reference fuels.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.2.1 Exception—The values given in parentheses are for information only.
1.3 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.
1.4 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. Summary of Test Method
2.1 The sample is injected into a capillary gas chromatographic column consisting of at least 61 m (200 ft) 61 m (200 ft) of
stainless steel tubing (0.25-mm (0.010-in.)(0.25 mm (0.010 in.) inside diameter), the inner walls of which are coated with a thin
film of stationary liquid. An inert gas transports the sample through the column, in which it is partitioned into its individual
components. As each component is eluted from the column, it is detected with a hydrogen flame ionization detector and recorded
on a conventional strip-chart recording potentiometer. The detector response from each impurity is then compared with that of a
known quantity of an internal standard. After determining the total impurity concentration, the n-heptane, or isooctane purity is
obtained by difference.
3. Significance and Use
3.1 This test method is used for specification analysis of high-purity n-heptane and isooctane, which are used as ASTM Knock
Test Reference Fuels. Hydrocarbon impurities or contaminants, which can adversely affect the octane number of these fuels, are
precisely determined by this method.
4. Apparatus
4.1 Chromatograph—Gas chromatograph should be equipped with a split-stream inlet device for introducing minute quantities
of sample without fractionation, a capillary column, and a hydrogen flame ionization detector. An electrometer to amplify the low
output signal of the hydrogen flame ionization detector, and a strip-chart recorder for recording the detector signal are needed. The
time constant of neither the electrometer nor the recorder should exceed 1 s. 1 s. A ball and disk integrator or electronic integrator
for peak area measurements should be used. The detection system must have sufficient sensitivity to produce a recorder deflection
for cyclohexane of at least 8 divisions on a standard 0–100 scale chart using 0.10 0.10 % by volume percent of cyclohexane in
n-heptane as defined in 7.1.
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.04.0L on Gas Chromatography Methods.
Current edition approved Oct. 1, 2013Oct. 1, 2017. Published October 2013November 2017. Originally approved in 1964. Last previous edition approved in 20082013
as D2268 – 93 (2013).(2008). DOI: 10.1520/D2268-93R13.10.1520/D2268-93R17.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2268 − 93 (2017)
4.2 Microsyringe—A microsyringe is needed for injecting the sample into the split-stream inlet device.
4.3 Volumetric Pipet, 0.1-mL0.1 mL capacity.
4.4 Analytical Balance, 200-g200 g capacity.
5. Reagents and Materials
5.1 Carrier Gas—Argon, Nitrogen, or Helium; 99.99%99.99 % or greater purity. (Warning—Compressed gases under high
pressure.)
5.2 Fuel Gas—Hydrogen; 99.99%99.99 % or greater purity. (Warning—Compressed gas under high pressure. Extremely
flammable gas.)
5.3 Oxidant Gas—Air; 99.99%99.99 % or greater purity. (Warning—Compressed gases under high pressure.)
5.4 Cyclohexane—At least 99 mol % pure, to be used as internal standard. (Warning—Flammable liquid and harmful if
ingested or inhaled.)
5.5 n-Pentane—Commercial grade. (Warning—Volatile and flammable liquid, and harmful if ingested or inhaled.)
5.6 Isooctane (2,2,4-trimethylpentane)—(Warning—Flammable liquid and harmful if ingested or inhaled.)
5.7 Squalane—Liquid phase for gas chromatographic columns.
5.8 Tubing—Type 316, 321, or 347 stainless steel; 0.25 mm (0.010 in.) 0.25 mm (0.010 in.) inside diameter.
6. Preparation of Resolving Column
NOTE 1—There are many different procedures for coating capillary columns. A suitable procedure is given in 6.1 through 6.3. Other columns may be
used provided they meet resolution and repeatability requirements of the method.
6.1 Connect a 229 mm (9-in.) 229 mm (9 in.) section of stainless steel tubing 6.4 mm 6.4 mm ( ⁄4-in.) in.) outside diameter, total
volume of approximately 5 mL) 5 mL) to a high-pressure cylinder of argon, helium, or nitrogen through a pressure regulator.
Connect at least 61 m (200 ft) 61 m (200 ft) of Type 316, 321, or 347 stainless steel tubing (0.25-mm (0.010-in.)(0.25 mm
(0.010 in.) inside diameter) to the 229-mm229 mm section of 64 mm 64 mm tubing which is to be used as a reservoir for the
coating solution. The capillary column is generally coiled on a suitable mandrel before coating. To the other end of the capillary
column, connect an additional 3030 m to 9 to 12 m (40 ft) 9 m to 12 m (40 ft) of capillary tubing through a 1.6 mm 1.6 mm
( ⁄16-in.) in.) Swagelok union.
6.2 Clean the tubing by passing 2525 mL to 30 mL 30 mL (5 to 6 reservoir volumes) of n-pentane through the tubing with about
1.7 to 2.1 MPa ( 250 to 300 psig 1.7 MPa to 2.1 MPa (250 psig to 300 psig gage) of inert gas. After the column has been cleaned,
disconnect the upstream end of the reservoir tube and allow the pressure in the tubing to return to atmospheric.
6.3 Prepare a solution containing 6 volume percent of squalane in n-pentane. Fill the reservoir tube with the coating solution
and promptly connect to the gas cylinder. Pass the coating solution through the column at 500 psig (3.5 MPa 500 psig (3.5 MPa
gage) until the solution begins issuing from the end of the capillary tubing; gradually reduce the inlet pressure in order to keep
the flow of the solution at a relatively even rate of 4040 drops ⁄min to 6060 drops drops/min. ⁄min. When the coating solution has
been expelled from the column, reduce the inlet pressure to 345 kPa (50 psig 345 kPa (50 psig gage) and allow gas to pass through
the column for 11 h to 2 h. 2 h. Disconnect the 99 m to 12-m (3012 m (30 ft to 40-ft)40 ft) tail section and then mount the column
in the chromatograph.
6.4 To test column resolution use Fig. 1 and calculate R, from the distance between the cyclohexane and n-heptane peaks at the
peak maxima, d, and the widths of the peaks at the baseline, Y and Y .
1 2
R 5 2 d 2 d / Y 1Y (1)
~ ! ~ !
1 2 1 2
Resolution (R), using the above equation, must exceed a value of 10.
FIG. 1 Column Resolution (R).
D2268 − 93 (2017)
7. Sample Preparation
7.1 Place 2020 mL to 30 mL 30 mL of the reference fuel (n-heptane or isooctane) into a 100-mL100 mL volumetric flask which
has been previously weighed.
7.2 Weigh the sample. Using a 0.10-mL0.10 mL volumetric pipet, add 0.10 mL 0.10 mL of the internal standard cyclohexane
(99 mol %, min) and reweigh. Dilute to the mark with the n-heptane or isooctane sample and weigh. Use a 200-g200 g analytical
balance accurate to 60.0002 g. 60.0002 g. From these weights (masses) and the
...