ASTM D2268-93(2003)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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An American National Standard
e1
Designation:D2268–93 (Reapproved 2003)
Standard Test Method for
Analysis of High-Purity n-Heptane and Isooctane by Capillary
Gas Chromatography
This standard is issued under the fixed designation D 2268; 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.
This standard has been approved for use by agencies of the Department of Defense.
e NOTE—Warning notes were editorially moved into the standard text in July 2003.
1. Scope 3. Significance and Use
1.1 This test method provides for the analysis of high-purity 3.1 This test method is used for specification analysis of
(greater than 99.5 % by volume) n-heptane and isooctane high-purity n-heptane and isooctane, which are used asASTM
(2,2,4-trimethylpentane), which are used as primary reference Knock Test Reference Fuels. Hydrocarbon impurities or con-
standards in determining the octane number of a fuel. Indi- taminants, which can adversely affect the octane number of
vidual compounds present in concentrations of less than these fuels, are precisely determined by this method.
0.01 % can be detected. Columns specified by this test method
4. Apparatus
may not allow separation of all impurities in reference fuels.
4.1 Chromatograph—Gas chromatograph should be
1.2 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information equipped with a split-stream inlet device for introducing
minute quantities of sample without fractionation, a capillary
only.
1.3 This standard does not purport to address all of the column, and a hydrogen flame ionization detector. An elec-
trometertoamplifythelowoutputsignalofthehydrogenflame
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- ionization detector, and a strip-chart recorder for recording the
detector signal are needed. The time constant of neither the
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. electrometernortherecordershouldexceed1s.Aballanddisk
integrator or electronic integrator for peak area measurements
2. Summary of Test Method
should be used. The detection system must have sufficient
2.1 The sample is injected into a capillary gas chromato- sensitivity to produce a recorder deflection for cyclohexane of
graphic column consisting of at least 61 m (200 ft) of stainless at least 8 divisions on a standard 0–100 scale chart using 0.10
steel tubing (0.25-mm (0.010-in.) inside diameter), the inner volume percent of cyclohexane in n-heptane as defined in 7.1.
walls of which are coated with a thin film of stationary liquid. 4.2 Microsyringe—A microsyringe is needed for injecting
An inert gas transports the sample through the column, in the sample into the split-stream inlet device.
which it is partitioned into its individual components. As each 4.3 Volumetric Pipet, 0.1-mL capacity.
component is eluted from the column, it is detected with a 4.4 Analytical Balance, 200-g capacity.
hydrogen flame ionization detector and recorded on a conven-
5. Reagents and Materials
tional strip-chart recording potentiometer. The detector re-
sponse from each impurity is then compared with that of a 5.1 Carrier Gas—Argon, Nitrogen, or Helium; 99.99% or
greater purity. (Warning—Compressed gases under high pres-
known quantity of an internal standard. After determining the
total impurity concentration, the n-heptane, or isooctane purity sure.)
5.2 Fuel Gas—Hydrogen; 99.99% or greater purity.
is obtained by difference.
(Warning—Compressed gas under high pressure. Extremely
flammable gas.)
This test method is under the jurisdiction of ASTM Committee D02 on
5.3 Oxidant Gas—Air; 99.99% or greater purity.
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
(Warning—Compressed gases under high pressure.)
D02.04 on Hydrocarbon Analysis.
Current edition approved May 10, 2003. Published July 2003. Originally
approved in 1964. Last previous edition approved in 1998 as D 2268–93 (1998).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
e1
D2268–93 (2003)
5.4 Cyclohexane—At least 99 mol % pure, to be used as from the distance between the cyclohexane and n-heptane
internalstandard.(Warning—Flammableliquidandharmfulif peaks at the peak maxima, d, and the widths of the peaks at the
ingested or inhaled.) baseline, Y and Y .
1 2
5.5 n-Pentane—Commercial grade. (Warning—Volatile
R 5 2~d 2 d !/~Y 1 Y ! (1)
1 2 1 2
and flammable liquid, and harmful if ingested or inhaled.)
Resolution (R), using the above equation, must exceed a
5.6 Isooctane (2,2,4-trimethylpentane)—(Warning—
value of 10.
Flammable liquid and harmful if ingested or inhaled.)
5.7 Squalane—Liquid phase for gas chromatographic col-
7. Sample Preparation
umns.
5.8 Tubing—Type 316, 321, or 347 stainless steel; 0.25 mm
7.1 Place 20 to 30 mL of the reference fuel (n-heptane or
(0.010 in.) inside diameter.
isooctane) into a 100-mL volumetric flask which has been
previously weighed.
6. Preparation of Resolving Column
7.2 Weigh the sample. Using a 0.10-mL volumetric pipet,
NOTE 1—There are many different procedures for coating capillary add 0.10 mL of the internal standard cyclohexane (99 mol %,
columns.Asuitable procedure is given in 6.1 through 6.3. Other columns
min) and reweigh. Dilute to the mark with the n-heptane or
may be used provided they meet resolution and repeatability requirements
isooctane sample and weigh. Use a 200-g analytical balance
of the method.
accurate to 60.0002 g. From these weights (masses) and the
6.1 Connect a 229 mm (9-in.) section of stainless steel
relative density (specific gravities) of cyclohexane and
tubing 6.4 mm ( ⁄4-in.) outside diameter, total volume of
n-heptane or isooctane, calculate the volume percent of the
approximately 5 mL) to a high-pressure cylinder of argon,
cyclohexane internal standard to the nearest 0.001 volume
helium, or nitrogen through a pressure regulator. Connect at
percent. (Relative density (specific gravity) of cyclohexane at
least 61 m (200 ft) of Type 316, 321, or 347 stainless steel
20°C = 0.7786; n-heptane = 0.6838, and 2,2,4-
tubing (0.25-mm (0.010-in.) inside diameter) to the 229-mm
trimethylpentane = 0.6919.)
section of 64 mm tubing which is to be used as a reservoir for
Cyclohexane, volume % 5 wt cyclohexane/rel dens cyclohexane
the coating solution. The capillary column is generally coiled
4~wt reference fuel/rel dens reference fuel!3 100 (2)
on a suitable mandrel before coating. To the other end of the
capillary column, connect an additional 30 to 9 to 12 m (40 ft)
8. Procedure
of capillary tubing through a 1.6 mm ( ⁄16-in.) Swagelok union.
8.1 Adjust the operating variables to optimum conditions.
6.2 Clean the tubing by passing 25 to 30 mL (5 to 6
Temperatures should be as follows: Injection port and splitter
reservoir volumes) of n-pentane through the tubing with about
150 to 250°C, column at optimum temperature and detector
1.7 to 2.1 MPa ( 250 to 300 psig gage) of inert gas. After the
greater than 100°C. Adjust the excess gas flow through the
column has been cleaned, disconnect the upstream end of the
splitter to provide a proper sample size to the column.
reservoir tube and allow the pressure in the tubing to return to
8.2 Usingthemicrosyringe,injectsufficientsamplecontain-
atmospheric.
ing the internal standard. Both the sample volume and the split
6.3 Prepare a solution containing 6 volume percent of
ratio must be considered in choosing the correct volume of
squalane in n-pentane. Fill the reservoir tube with the coating
sample to inject. Volumes entering the column in the range of
solu
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