ASTM D2268-93(1998)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
An American National Standard
Designation: D 2268 – 93 (Reapproved 1998)
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.
1. Scope Knock Test Reference Fuels. Hydrocarbon impurities or con-
taminants, which can adversely affect the octane number of
1.1 This test method provides for the analysis of high-purity
these fuels, are precisely determined by this method.
(greater than 99.5 % by volume) n-heptane and isooctane
(2,2,4-trimethylpentane), which are used as primary reference
4. Apparatus
standards in determining the octane number of a fuel. Indi-
4.1 Chromatograph—Gas chromatograph should be
vidual compounds present in concentrations of less than
equipped with a split-stream inlet device for introducing
0.01 % can be detected. Columns specified by this test method
minute quantities of sample without fractionation, a capillary
may not allow separation of all impurities in reference fuels.
column, and a hydrogen flame ionization detector. An elec-
1.2 The values stated in SI units are to be regarded as the
trometer to amplify the low output signal of the hydrogen flame
standard. The values given in parentheses are for information
ionization detector, and a strip-chart recorder for recording the
only.
detector signal are needed. The time constant of neither the
1.3 This standard does not purport to address all of the
electrometer nor the recorder should exceed 1 s. A ball and disk
safety concerns, if any, associated with its use. It is the
integrator or electronic integrator for peak area measurements
responsibility of the user of this standard to establish appro-
should be used. The detection system must have sufficient
priate safety and health practices and determine the applica-
sensitivity to produce a recorder deflection for cyclohexane of
bility of regulatory limitations prior to use. For specific
at least 8 divisions on a standard 0–100 scale chart using 0.10
precautionary statements see Notes 1-3.
volume percent of cyclohexane in n-heptane as defined in 7.1.
2. Summary of Test Method 4.2 Microsyringe—A microsyringe is needed for injecting
the sample into the split-stream inlet device.
2.1 The sample is injected into a capillary gas chromato-
4.3 Volumetric Pipet, 0.1-mL capacity.
graphic column consisting of at least 61 m (200 ft) of stainless
4.4 Analytical Balance, 200-g capacity.
steel tubing (0.25-mm (0.010-in.) inside diameter), the inner
walls of which are coated with a thin film of stationary liquid.
5. Reagents and Materials
An inert gas transports the sample through the column, in
5.1 Carrier Gas—Argon, Nitrogen, or Helium; 99.99% or
which it is partitioned into its individual components. As each
greater purity. (Warning—See Note 1.)
component is eluted from the column, it is detected with a
hydrogen flame ionization detector and recorded on a conven-
NOTE 1—Warning: Compressed gases under high pressure.
tional strip-chart recording potentiometer. The detector re-
5.2 Fuel Gas—Hydrogen; 99.99% or greater purity.
sponse from each impurity is then compared with that of a
(Warning—See Note 2.)
known quantity of an internal standard. After determining the
NOTE 2—Warning: Compressed gas under high pressure. Extremely
total impurity concentration, the n-heptane, or isooctane purity
flammable gas.
is obtained by difference.
5.3 Oxidant Gas—Air; 99.99% or greater purity.
3. Significance and Use
(Warning—See Note 1.)
3.1 This test method is used for specification analysis of
5.4 Cyclohexane—At least 99 mol % pure, to be used as
high-purity n-heptane and isooctane, which are used as ASTM
internal standard. (Warning—See Note 3.)
NOTE 3—Warning: Flammable liquid and harmful if ingested or in-
haled.
This test method is under the jurisdiction of ASTM Committee D-2 on
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
5.5 n-Pentane—Commercial grade. (Warning—See Note
D02.04 on Hydrocarbon Analysis.
4.)
Current edition approved Feb. 15, 1993. Published May 1993. Originally pub-
lished as D 2268 – 64. Last previous edition D 2268 – 86.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2268 – 93 (1998)
NOTE 4—Warning: Volatile and flammable liquid, and harmful if
from the distance between the cyclohexane and n-heptane
ingested or inhaled.
peaks at the peak maxima, d, and the widths of the peaks at the
baseline, Y and Y .
5.6 Isooctane (2,2,4-trimethylpentane)—(Warning—See
1 2
Note 3.)
R 5 2~d 2 d !/~Y 1 Y ! (1)
1 2 1 2
5.7 Squalane—Liquid phase for gas chromatographic col-
Resolution (R), using the above equation, must exceed a
umns.
value of 10.
5.8 Tubing—Type 316, 321, or 347 stainless steel; 0.25 mm
(0.010 in.) indise diameter.
7. Sample Preparation
6. Preparation of Resolving Column
7.1 Place 20 to 30 mL of the reference fuel (n-heptane or
isooctane) into a 100-mL volumetric flask which has been
NOTE 5—There are many different procedures for coating capillary
previously weighed.
columns. A suitable procedure is given in 6.1 through 6.3. Other columns
7.2 Weigh the sample. Using a 0.10-mL volumetric pipet,
may be used provided they meet resolution and repeatability requirements
of the method.
add 0.10 mL of the internal standard cyclohexane (99 mol %,
min) and reweigh. Dilute to the mark with the n-heptane or
6.1 Connect a 229 mm (9-in.) section of stainless steel
isooctane sample and weigh. Use a 200-g analytical balance
tubing 6.4 mm ( ⁄4-in.) outside diameter, total volume of
accurate to 6 0.0002 g. From these weights (masses) and the
approximately 5 mL) to a high-pressure cylinder of argon,
relative density (specific gravities) of cyclohexane and
helium, or nitrogen through a pressure regulator. Connect at
n-heptane or isooctane, calculate the volume percent of the
least 61 m (200 ft) of Type 316, 321, or 347 stainless steel
cyclohexane internal standard to the nearest 0.001 volume
tubing (0.25-mm (0.010-in.) inside diameter) to the 229-mm
percent. (Relative density (specific gravity) of cyclohexane at
section of 64 mm tubing which is to be used as a reservoir for
20°C = 0.7786; n-heptane = 0.6838, and 2,2,4-
the coating solution. The capillary column is generally coiled
trimethylpentane = 0.6919.)
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)
Cyclohexane, volume % 5 wt cyclohexane/rel dens cyclohexane
4~wt reference fuel/rel dens reference fuel!3 100 (2)
of capillary tubing through a 1.6 mm ( ⁄16-in.) Swagelok union.
6.2 Clean the tubing by passing 25 to 30 mL (5 to 6
8. Procedure
reservoir volumes) of n-pentane through the tubing with about
1.7 to 2.1 MPa ( 250 to 300 psig gage) of inert gas. After the
8.1 Adjust the operating variables to optimum conditions.
column has been cleaned, disconnect the up-stream end of the
Temperatures should be as follows: Injection port and splitter
reservoir tube and allow the pressure in the tubing to return to
150 to 250°C, column at optimum temperature and detector
atmospheric.
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
8.2 Using the microsyringe, inject sufficient sample contain-
solution and promptly connect to the gas cylinder. Pass the
ing the internal standard. Both the sample volume and the split
coating solution through the column at 500 psig (3.5 MPa
ratio must be considered in choosing the correct volume of
gage) until the solution begins issuing from the end of the
sample to inject. Volumes entering the column in the range of
capillary tubing; graduall
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