ASTM D6550-00

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An American National Standard
Designation: D 6550 – 00
Standard Test Method for
Determination of Olefin Content of Gasolines by
Supercritical-Fluid Chromatography
This standard is issued under the fixed designation D 6550; 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 D 6293 Test Method for Oxygenates and Paraffin, Olefin,
Naphthene, Aromatic (O-PONA) Hydrocarbon Types in
1.1 This test method covers the determination of the total
Low-Olefin Spark Ignition Engine Fuels by Gas Chroma-
amount of olefins in blended motor gasolines and gasoline
tography
blending stocks by supercritical-fluid chromatography (SFC).
D 6296 Test Method for Total Olefins in Spark-ignition
Results are expressed in terms of mass % olefins. The
Engine Fuels by Multi-dimensional Gas Chromatography
application range is from 1 to 25 mass % total olefins.
D 6299 Practice for Applying Statistical Quality Assurance
1.2 This test method can be used for analysis of commercial
Techniques to Evaluate Analytical Measurement System
gasolines,includingthosecontainingvaryinglevelsofoxygen-
Performance
ates, such as methyl tert/butyl ether (MTBE), diisopropyl ether
(DIPE), methyl tert/amyl ether (TAME), and ethanol, without
3. Terminology
interference.
3.1 Definitions of Terms Specific to This Standard:
NOTE 1—This test method has not been designed for the determination
3.1.1 critical pressure, n—the pressure needed to condense
of the total amounts of saturates, aromatics, and oxygenates.
a gas to a liquid at the critical temperature.
1.3 The values stated in SI units are to be regarded as
3.1.2 critical temperature, n—the highest temperature at
standard. The values given in parentheses are for information
which a gaseous fluid can be condensed to a liquid by means
only.
of compression.
1.4 This standard does not purport to address all of the
3.1.3 supercritical fluid, n—a fluid maintained above its
safety concerns, if any, associated with its use. It is the
critical temperature and critical pressure.
responsibility of the user of this standard to establish appro-
3.1.4 supercritical-fluid chromatography (SFC), n—a type
priate safety and health practices and determine the applica-
of chromatography that employs a supercritical fluid as the
bility of regulatory limitations prior to use.
mobile phase.
2. Referenced Documents
4. Summary of Test Method
2.1 ASTM Standards:
4.1 A small aliquot of the fuel sample is injected onto a set
D 1319 Test Method for Hydrocarbon Types in Liquid
of two chromatographic columns connected in series and
Petroleum Products by Fluorescent-Indicator Adsorption
transported using supercritical carbon dioxide (CO)asthe
D 4052 Test Method for Density and Relative Density of
mobile phase. The first column is packed with high-surface-
Liquids by Digital Density Meter
area silica particles. The second column contains either high-
D 5186 Test Method for Determination of the Aromatic
surface-area silica particles loaded with silver ions or strong-
ContentandPolynuclearAromaticContentofDieselFuels
cation-exchange material loaded with silver ions.
and Aviation Turbine Fuels by Supercritical Fluid Chro-
4.2 Two switching valves are used to direct the different
matography
classes of components through the chromatographic system to
the detector. In a forward-flow mode, saturates (normal and
branchedalkanes,cyclicalkanes)passthroughbothcolumnsto
This test method is under the jurisdiction of ASTM Committee D02 on
the detector, while the olefins are trapped on the silver-loaded
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
column and the aromatics and oxygenates are retained on the
D02.04.0C on Liquid Phase Chromatography.
Current edition approved April 10, 2000. Published June 2000.
silica column. Aromatic compounds and oxygenates are sub-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
sequently eluted from the silica column to the detector in a
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
back-flush mode. Finally, the olefins are back-flushed from the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. silver-loaded column to the detector.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6550–00
TABLE 1 Typical Columns
Silica Column Silver-loaded Column
vendor Merck vendor Hypersil, Phenomenex, Selerity
Packing material Lichrospher SI 60 Packing material Hypersil SCX, Selectosil SCX, Ag+ form
Particle size, µm 5 particle size, µm 5
Length, mm 250 length, mm 100 or 50
Internal diameter, mm 4.6 internal diameter, mm 4.6
4.3 A flame-ionization detector (FID) is used for quantita- 6.1.2.1 AUVdetectorwithaverysmalldeadvolumecanbe
tion. Calibration is based on the area of the chromatographic inserted between the column and the FID and operated in
signal for olefins, relative to standard reference materials, series.
which contain a known mass % of total olefins as corrected for 6.1.2.2 A post-column splitting device, consisting of a
density. T-junctionwithanappropriateflowrestrictortotheFID,canbe
inserted between the column and the UV detector. Using the
5. Significance and Use T-junction, the two detectors can be operated in parallel. The
combination of restrictors (before the FID and after the UV
5.1 Gasoline-range olefinic hydrocarbons have been dem-
detector) shall allow the pump and detector to perform as
onstrated to contribute to photochemical reactions in the
specified.
atmosphere, which result in the formation of photochemical
6.1.3 Sample-inlet System—A liquid-sample injection
smog in susceptible urban areas.
valve is required, capable of introducing (sub-)microlitre
5.2 The CaliforniaAir Resources Board (CARB) has speci-
volume with a precision better than 0.5 %. A 1-µL injection
fied a maximum allowable limit of total olefins in motor
volume was found to be adequate in combination with 4.6-mm
gasoline. This necessitates an appropriate analytical test
inside diameter columns. Corresponding injection volumes are
method for determination of total olefins to be used both by
200 and 50 nL for columns with inside diameters of 2 and 1
regulators and producers.
mm, respectively. The sample inlet system shall be installed
5.3 This test method compares favorably with Test Method
and operated in a manner such that the chromatographic
D 1319 (FIA) for the determination of total olefins in motor
separation is not negatively affected.
gasolines. It does not require any sample preparation, has a
6.1.4 Columns—Two columns of equal inside diameter are
comparatively short analysis time of about 10 min, and is
required:
readily automated. Alternative methods for determination of
6.1.4.1 A high-surface-area-silica column, capable of sepa-
olefins in gasoline include Test Methods D 6293 and D 6296.
rating alkanes and olefins from aromatics as specified in
Section 8. Typically, one or several 250-mm long columns are
6. Apparatus
used. These columns are packed with particles having an
6.1 Supercritical-fluid Chromatograph (SFC)—Any SFC
average diameter of 5 µm or less, 600-nm (60-Å) pores, and a
instrumentation can be used that has the following character-
surface area of$350 m /g.
istics and meets the performance requirements specified in
NOTE 3—Columns suitable for Test Method D 5186 are also suitable
Section 8.
for the present method. A typical example is shown in Table 1.
NOTE 2—The SFC instruments suitable for Test Method D 5186 are
6.1.4.2 A silver-loaded-silica column or a cation-exchange
suitable for this test method, if equipped with two switching valves, as
described under 6.1.7. column in the silver form. Cation-exchange columns are
claimed to yield more stable columns. Typically, one 50 or
6.1.1 Pump—The SFC pump shall be able to operate at the
100-mm long column packed with particles with an average
required pressures (typically up to about 30 MPa) and deliver
diameter of 5 µm is used for the analysis.
a sufficiently stable flow to meet the requirements of retention-
time precision (better than 0.3 %) and detection background
NOTE 4—Some columns that have been used successfully are shown in
Table 1.
(see Section 8). The characteristics of the pump will largely
determine the optimum column diameter. The use of 4.6-mm
6.1.5 Column-temperature Control—The chromatograph
internal diameter (i.d.) columns requires a pump capacity of at
shall be capable of column temperature control to within 0.5°C
least1mL/minofliquidCO .Columnswithaninsidediameter
2 or less.
of 2 and 1 mm require minimum pump capacities of 200 and
6.1.6 Computor or Electronic Integrator—Means shall be
50 µL/min, respectively.
providedforthedeterminationofaccumulatedpeakareas.This
6.1.2 Detectors—AFID is required for quantitation.Aflow
can be done by means of a computer or electronic integrator.
restrictor shall be installed immediately before the FID. This
The computer or integrator shall have the capability of correct-
restrictor serves to maintain the required pressure in the
ing for baseline shifts during the run.
column, while allowing the pump and detector to perform as
specified. A (diode-array or variable wavelength) UV detector
Sample valves with loop volumes down to 50 nL are commercially available
for establishing optimum switching times (see Sections 8 and
from Valco (Houston, TX).
9) is optional. Such a detector can be incorporated in two
Anderson, P. E., Demirbueker, M., and Blomberg, L. G., Journal of Chroma-
different manners. tography, 596, 1991, pp. 301-311.
D6550–00
FIG. 1 Configuration of Switching Valves (Shown in Position A)
6.1.7 Switching Valves—Two six-way switching valves are 7.2 Air—Zero-grade (hydrocarbon-free) air is used as the
configured in accordance with the scheme shown in Fig. 1. FID oxidant. (Warning—Air is usually supplied as a com-
This configuration allows four different valve positions, de- pressed gas under high pressure, and it supports combustion.)
fined as follows: 7.3 Calibration Solution—A mixture of hydrocarbons with
6.1.7.1 Position A—Silica column (forward-flush mode) a known mass % of olefins of the type and concentration found
and silver-loaded column (forward-flush mode) connected in in typical gasolines. This olefin mixture can be diluted by
series. This position is used (a) to inject the sample on the two weight with olefin-free components, such as alkylate, toluene,
columns, (b) to elute the saturates, (c) to trap the olefins on the xylenes, and oxygenates, such as MTBE, as appropriate to
silver-loaded column, and (d) to retain the aromatics and approximate the composition of the fuels being tested.
oxygenates on the silica column. 7.4 Carbon Dioxide (CO )—Supercritical-fluid-
6.1.7.2 Position B—Silica column (backflush mode) con- chromatographic grade, 99.99 % minimum purity, supplied
nected in-line; silver-loaded column not in flow path. This pressurized in a cylinder with a dip tube for removal of liquid
position is used to elute the aromatics and polar compounds. CO.(Warning—Liquid at high pressure. Release of pressure
6.1.7.3 Position C—Silica column not in flow path; silver- results in production of extremely cold, solid CO and gas,
loaded column (backflush mode) connected in-line. This posi- which can dilute available atmospheric oxygen.)
tion is used to elute the olefins. 7.5 Hydrogen—Hydrogen of high quality (hydrocarbon-
6.1.7.4 Position D—Silica column (forward-flush mode) free) is used as the fuel for the FID. (Warning—Hydrogen is
connected in-line; silver-loaded column not in flow path. This usually supplied under high pressure and is extremely flam-
position is used to optimize the separation. Also, this position mable.)
allows Test Method D 5186 to be performed without changing 7.6 Loading-time Mixture—A mixture of a typical alkane
the system. and an olefin, which can be used to determine the loading time
(see 8.2.2.3 (a) and 8.2.2.3 (b)) while protecting the silver-
7. Reagents and Materials
loaded column from exposure to aromatic compounds.
7.1 Purity of Reagents—Reagent grade chemicals shall be 7.7 Performance Mixture—Amixture of a typical alkane, a
used in all tests. Unless otherwise indicated, it is intended that mono-aromatic (usually toluene), and a typical mono-olefin
all reagents conform to the specifications of the Committee on can be used to fine-tune this test method and to check its
Analytical Reagents of the American Chemical Society where performance. A mixture of n-heptane, toluene, and 3-methyl-
2-pentene has been successfully used for this purpose.
such specifications are available. Other grades may be used,
provided it is first ascertained that the reagent is of sufficiently 7.8 Quality Control Sample—A motor gasoline containing
olefins to be used to establish and monitor the precision of the
high purity to permit its use without lessening the accuracy of
the determination. analytical measurement system.
8. Preparation of Apparatus
8.1 Install the SFC instrumentation in accordance with the
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
manufacturer’s instructions. System operating conditions will
listed by the American Chemical Society, see Analar Standards for Laboratory
depend on the column used and optimization of performance.
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
The conditions listed inTable 1 have been used successfully. If
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. the performance characteristics in terms of retention and
D6550–00
resolution, specified in 8.2, are not achieved, the temperature, any peaks (S ) to within 0.1 % of the height of the
Baseline
pressure, or mobile-phase flow rate can be modified to achieve aromatics peak (h ), that is,
Aromatics
compliance.Asilica column of low activity can be reactivated
S # S 1 h / 1000 (2)
End Baseline Aromatics
by solvent rinsing, using accepted liquid-chromatographic
8.2.2.3 Silver-loaded Column—This column is operated
activation strategies.
exclusively as an olefin trap. Its stability and chromatographic
8.2 System Performance:
efficiency are not critical as long as the following two require-
8.2.1 System Optimization—The operation of the SFC sys-
ments are met. The column shall allow a quantitative separa-
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