ASTM D7754-23

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: D7754 − 19 D7754 − 23
Standard Test Method for
Determination of Trace Oxygenates in Automotive Spark-
Ignition Engine Fuel by Multidimensional Gas
Chromatography
This standard is issued under the fixed designation D7754; 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.
1. Scope*
1.1 This test method covers the determination of trace oxygenates in automotive spark-ignition engine fuel. The method used is
a multidimensional gas chromatographic method using 1,2-dimethoxy ethane as the internal standard. The oxygenates that are
analyzed are: methyl-tertiary butyl ether (MTBE), ethyl-tertiary butyl ether (ETBE), diisopropyl ether (DIPE), methanol,
tertiary-amyl methyl ether (TAME), n-propanol, i-propanol, n-butanol, i-butanol, tert-butyl alcohol, sec-butyl alcohol, and
tert-pentanol. Ethanol is usually not measured as a trace oxygenate since ethanol can be used as the main oxygenate compound
in finished automotive spark-ignition fuels such as reformulated automotive spark-ignition fuels. The concentration range of the
oxygenates covered in the ILS study was from 10 mg ⁄kg to 2000 mg ⁄kg. In addition this method is also suitable for the
measurement of the C5 isomeric alcohols (2-methyl-1-butanol, 2-methyl-2-butanol) present from the fermentation of ethanol.
1.2 The ethanol blending concentration for which this test method applies ranges from 1 % to 15% by volume. Higher
concentrations of ethanol coelute with methanol in the analytical column. Lower levels of ethanol, similar to the other oxygenate,
can be calibrated and analyzed also. If higher ethanol concentrations are expected, the window cutting technique can be used to
avoid ethanol from entering the analytical column and interfere with the determination of the other oxygenates of interest. Refer
to Appendix X1 for details.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3.1 Alternative units, in common usage, are also provided to increase clarity and aid the users of this test method.
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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 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. Referenced Documents
2.1 ASTM Standards:
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 Nov. 1, 2019Nov. 1, 2023. Published December 2019November 2023. Originally approved in 2011. Last previous edition approved in 20162019
as D7754 – 16.D7754 – 19. DOI:10.1520/D7754-19.DOI:10.1520/D7754-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4307 Practice for Preparation of Liquid Blends for Use as Analytical Standards
D4815 Test Method for Determination of MTBE, ETBE, TAME, DIPE, tertiary-Amyl Alcohol and C to C Alcohols in
1 4
Gasoline by Gas Chromatography
D6304 Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl
Fischer Titration
E355 Practice for Gas Chromatography Terms and Relationships
3. Terminology
3.1 Definitions:
3.1.1 This test method makes reference to common gas chromatographic procedures, terms, and relationships. Detailed definitions
of these can be found in Practice E355 or Terminology D4175, or both.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 electronic pressure control, n—electronic pneumatic control of carrier gas flows. Can be flow or pressure programmed to
speed up elution of components.
3.2.2 flame ionization detector (FID), n—detector used to analyze the components eluting from the column.
3.2.3 fluidic switch, n—device that reverses the directional flow in a union T altering the pressure at the midpoint. In its simplest
design it is also known as a Dean Switch.
3.2.4 inlet, n—capillary split/splitless inlet system operated in the split mode is recommended. Operate the inlet within its linear
range.
3.2.4.1 split ratio, n— in capillary gas chromatography, the ratio of the total flow of carrier gas to the sample inlet versus the
flow of the carrier gas to the capillary column is expressed by:
Split ratio 5 ~S1C!/C (1)
where:
S = flow rate at the splitter vent, and
C = flow rate at the column outlet.
3.2.5 low volume connector, n—special union for connecting two lengths of tubing 1.6 mm inside diameter and smaller.
Sometimes this is referred to as zero dead volume union.
3.2.6 multidimensional gas chromatography, n—gas chromatographic technique where using hardware (valves, pressure switches,
etc.) in which selected components from one column (primary column) are transferred to a secondary column differing in
characteristics (film thickness, polarity, capacity, etc.) from the first column.
3.2.7 WCOT column, n—wall-coated open tubular, a type of capillary gas chromatographic column prepared by coating the inside
of the capillary wall with a specified thin film of stationary phase. The coatings used are either 100 % polydimethyl siloxane or
5 % phenyl-polydimethylsiloxane.
3.2.7.1 apolar column, n—polydimethylsiloxane nonpolar column used as a pre-column.
3.2.7.2 PLOT column-oxygen selective, n—porous-layer open tubular which is an oxygenate selective capillary gas-solid
chromatographic column. It is used as an analytical column.
4. Summary of Test Method
4.1 An appropriate internal standard of a product that is not present in refinery streams, such as 1,2-dimethoxy ethane (1,2-DME),
is added to the sample, which is then introduced into a gas chromatograph equipped with two columns and a 4-port switching
valve. The sample first passes onto an apolar (non-polar) polydimethylsiloxane WCOT column that performs a pre-separation of
the trace oxygenates and elutes unwanted high boiling hydrocarbons to vent. The oxygenates and the DME are transferred to the
analytical oxygen selective column by the switching valve. While the oxygenates and the DME are eluting from the analytical
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column, the inlet’s carrier gas is used to elute the hydrocarbons from the pre-column to yield a stable baseline for the next analysis.
The auxiliary pressure controller is used to provide carrier gas to the analytical column during the analysis.
4.2 The eluted components Table 1 are detected by one or two flame ionization detectors. In the single detector Configuration A
(Fig. 1), only the components eluting from the analytical column are analyzed. In the two detector Configuration B (Fig. 2),
detector one is used to monitor the apolar elution and aid in setting “heart-cut” times for specific oxygenates while the second
detector is used to monitor the analytical column elution and also for the quantitation of the oxygenates. The second detector
response is proportional to the oxygenates and DME components concentration. The signal is recorded, the peak areas are
measured, and the concentration of each oxygenate is calculated with reference to the internal standard.
4.3 Alternatively, a fluidic switching system, Configuration C (Figs. 3 and 4) may be used instead of valve switching. In this
system, the two columns are joined by a zero dead volume (ZDV) tee purged by an auxiliary carrier source. At injection, the
auxiliary flow is low, and the inlet flow is sufficient so that at the midpoint where the two columns join, the flow is the required
flow to transfer the oxygenates to the PLOT column. Thus, there is forward flow through the pre-column and the analytical column.
Once the oxygenates have passed through to the analytical column, the inlet flow is decreased and the auxiliary flow is increased,
which results in backflushing the pre-column through the split vent of the front inlet while the analytical column continues the
separation.
5. Significance and Use
5.1 The analysis of trace oxygenates in automotive spark-ignition engine fuel has become routine in certain areas to ensure
compliance whenever oxygenated fuels are used. In addition, test methods to measure trace levels of oxygenates in automotive
spark-ignition fuel are necessary to assess product quality.
6. Apparatus
6.1 Chromatograph—A multidimensional gas chromatographic system, which is able to adequately resolve oxygenates and an
internal standard and to eliminate hydrocarbon, as well as other interferences, is used for these analyses. The instrument is to be
configured to operate using the approximate conditions listed in Table 2. The system requires a column switching mechanism
equivalent to Fig. 1 or Fig. 2 if using a valve system. If using a fluidic system then the fluidic switch and auxiliary flow control
are required as shown in Fig. 3 and Fig. 4. Carrier gas flow controllers (EPC) shall be capable of precise control where the flow
rates are low. Pressure control devices and gages shall be capable of precise control for the typical pressures required.
6.1.1 Detector—Two-flame ionization detectors are preferably used (Configuration B), although the analysis can be performed
using only one detector (Configuration A and C). The system shall have sufficient sensitivity and stability to obtain a signal-to-noise
ratio of at least 5 to 1 for a 1 mg ⁄kg concentration of any oxygenate. In the fluidic system only one detector is used.
6.1.2 Switching Valve—A switching valve, to be located within the gas chromatographic column oven or separate oven, capable
of performing the functions described in 9.2 and illustrated in Fig. 1. The valve shall be of low volume design and not contribute
significantly to chromatographic deterioration. Alternatively a Deans switching arrangement can also be used as shown in Fig. 3
and Fig. 4.
A
TABLE 1 Component List with Retention and Calibration Characteristics for WCOT/PLOT Column Set Using Conditions of Table 2
Component RT (min) Mol Wt BP (°C) Slope y-Int Corr. Coef.
ETBE 12.7 102.2 70 to 72 1.919 –0.02 0.999
MTBE 12.8 88.2 55 to 56 1.689 0.01 0.999
DIPE 12.9 102.2 68 to 69 2.124 –0.06 0.999
TAME 13.6 102.2 85 to 86 2.023 –0.02 0.999
Methanol 15.6 32.0 65 0.779 –0.09 0.997
Ethanol 18.7 46.1 78 1.352 0.19 0.999
iso-Propanol 22.2 60.1 81 to 83 1.504 –0.06 0.999
n-Propanol 22.2 60.1 97 . . .
t-Butanol 23.8 74.1 82 1.951 –0.12 0.999
s-Butanol 23.8 74.1 98 . . .
iso-Butanol 23.8 74.1 117 . . .
n-Butanol 24.4 74.1 118 1.906 –0.05 0.999
tert-Pentanol 25.1 88.1 102 2.148 –0.04 0.998
1,2-DME 26.0 90.1 85 . . .
A
For coeluting compounds the response is assigned to the first peak listed. Values may be different for different instruments.
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FIG. 1 Schematic of Chromatographic System—Configuration A
FIG. 2 Schematic of Chromatographic System—Configuration B
FIG. 3 Fluidic Switch Schematic—Oxygenate Transfer
6.1.2.1 A commercially available valve: 1.6 mm fittings, 0.75 mm ports was used in the method development. An equivalent valve
may be used.
6.1.2.2 Fluidic Switch, as an option to the two-position switching valve. See 4.3, Table 2, and Figs. 3 and 4 for a description.
Additional flow source is required as well as hardware, which is located in the oven for the column connection.
6.1.2.3 Some gas chromatographs are equipped with an auxiliary oven, which can be used to contain the valve at an isothermal
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FIG. 4 Fluidic Switch Schematic—Pre-column Backflush
TABLE 2 Chromatographic Conditions
Configuration Switching Valve Fluidic Switch
Carrier Gas Helium Helium
Injection Volume 1.0 μL 1.0 μL
Inlet: Split/Splitless (Split mode) Split/Splitless (Split mode)
Temperature 250 °C 250 °C
Split Ratio 10:1 10:1
A
Pressure 51.7 kPa, Constant Pressure 17.8 kPa, Flow Program Mode
Columns and Flows
Pre-column 30 m by 0.53 mm by 5.0 μm PDMS 15 m by 0.53 mm by 1.5 μm 5 % phenyl PDMS
7.5 mL/min @ 60 °C Initial Flow: 5.4 mL/min @ 60 °C
Hold for 1.5 min
Ramp: 90 mL/min to -5 mL/min
Hold until end of run
Analytical Column 10 m by 0.53 mm by 10 μm Oxygen Selective 10 m by 0.53 mm by 10 μm Oxygen Selective
7.5 mL/min@ 60 °C 7.0 mL/min constant flow
Oven:
Initial Temperature 60 °C 60 °C
Initial Hold 6.0 min 6.0 min
Ramp 1 10 °C ⁄min 10 °C ⁄min
Final Temperature 150 °C 150 °C
Final Hold 5.0 min 5.0 min
Ramp 2 10 °C ⁄min 10 °C ⁄min
Final Temperature 220 °C 220 °C
Final Hold 3.0 min 3.0 min
Total Time 30 min 30 min
Detector: FID FID
Temperature 275 °C 275 °C
Hydrogen 40 mL/min 40 mL/min
Air 450 mL/min 450 mL/min
Make-up (N2) 10 mL/min 10 mL/min
Valve Temperature 150 °C N/A
Auxiliary Pressure 73.1 kPa 10.3 kPa
Vent Restrictor 76 cm in length N/A
0.16 cm (O.D.) and 0.25 mm (I.D.) SS
Default Valve Times (for complete analysis):
Initial OFF N/A
0.50 min ON N/A
4.50 min OFF N/A
A
For Configuration A valve timing determination, 9.2, set the inlet pressure to 34.5 kPa.
temperature. In such a configuration, the two capillary columns are located in the main oven and connected to the valve by using
low dead volume and inert stainless steel tubing terminated in the GC oven.
6.1.2.4 An automatic valve switching device is used to ensure repeatable switching times. Such a device is synchronized with
injection and data collection times. For the pressure switching approach, automatic precise and stable pressure control shall be
used. Fluidic systems require both a fluidic switch and a programmable auxiliary pressure source to maintain and program flows.
6.1.3 Injection System—The chromatograph is to be equipped with a heated splitting-type inlet device containing a replaceable
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glass deactivated liner (single-taper style) with deactivated glass wool at the bottom to retain non-vaporized components). Split
injection is necessary to maintain the actual chromatographed sample size within the limits of column and detector efficiency and
linearity.
6.1.3.1 A microliter automatic syringe injector is used for introducing representative samples into the gas chromatographic inlet
and for adequate repeatability.
6.2 Data Acquisition System:
6.2.1 Computer—A data acquisition system containing a computer and data acquisition software is required.
6.2.2 Integrator—Alternatively, an integrator can be used to measure peak areas and to perform the analytical calculations.
6.3 Column Class:
6.3.1 Apolar (Non-polar) Pre-Column—This column performs a pre-separation of the oxygenates and internal standard from
hydrocarbons in the same boiling point range. Unless a separate auxiliary oven is provided for it, the apolar column shall perform
at the same temperature as the polar column does.
6.3.1.1 WCOT Methyl Silicone Pre-Column—30 m long by 0.53 mm inside diameter fused silica column with a 5 μm film
thickness of cross-linked polydimethylsiloxane. With fluidic switch (Configuration C) a 30 m long by 0.53 mm with a 1.5 μm 5 %
phenyl polydimethyl siloxane is recommended.
6.3.2 Polar Analytical Column—Any column with equivalent or better chromatographic efficiency and selectivity to that described
in 6.3.1 and which separation efficiency is illustrated in Figs. 5 and 6 can be used.
6.3.2.1 LowOx or GS OxyPLOT Polar Analytical Column—10 m long by 0.53 mm inside diameter fused silica PLOT column with
a 10 μm film thickness. These columns were used in the method development to provide the precision and bias data referred to
in Section 14.
7. Reagents and Materials
7.1 Gases:
FIG. 5 Oxygenate Elution Pattern, from WCOT Pre-column Only
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NOTE 1—Calibration Standard—250 mg ⁄kg oxygenates, 7.5 % ethanol, and 200 mg/kg internal standard in isooctane.
FIG. 6 Oxygenate Elution Pattern from WCOT/PLOT Column Set Using Conditions in Table 2
7.1.1 Helium, carrier gas, a minimum purity of 99.995 % is required. Oxygen scrubbers are recommended to safeguard the WCOT
columns.
7.1.2 For the FID, hydrogen (99.9995 % with air as the remainder) and nitrogen (99.995 %, as make up) are used.
(Warning—Observe high pressure precautions with all compressed gases. Observe flammable gas precautions with hydrogen.)
7.2 Standards for Calibration and Identification—Standards of oxygenates and the internal standard are required for establishing
identification by retention time as well as calibration for quantitative analysis. These materials shall be of known purity and free
of the other components to be analyzed. (Warning—These materials are flammable and can be harmful or fatal if ingested or
inhaled.). The following oxygenates: ethanol, methyl-tertiary butyl ether (MTBE), ethyl-tertiary butyl ether (ETBE), diisopropyl
ether (DIPE), methanol, tertiary-amyl methyl ether (TAME), n-propanol, i-propanol, n-butanol, i-butanol, tert-butyl alcohol,
sec-butyl alcohol, and tert-pentanol are to be used with the highest purity available (98 % to 99 %). Ethanol is usually not measured
as a trace sample component.
7.3 isooctane, or 2,2,4-Trimethylpentane—Used for preparation of calibration standards and dilution of automotive spark-ignition
fuel samples. In some cases, cyclohexane may be used provided it meets all of the requirements of the method. Using cyclohexane,
since it elutes in the cut window of the oxygenates, may cause difficulty in finding individual cut times (see Appendix X1).
(Warning—isooctane and cyclohexane are flammable and may be harmful if inhaled. High concentrations may cause
unconsciousness or death).
7.4 1,2-Dimethoxyethane (1,2-DME or ethylene glycol dimethyl ether)—Used as the internal standard. Use Reagent or
Chromatography grade.
8. Sampling
8.1 Every effort should be made to ensure that the sample is representative of the finished automotive spark-ignition fuel from
which it is taken. The use of multiple samples that are mixed or composite sampling is recommended. The use of epoxy-lined cans
are recommended for storage or shipping of the sample, or both. Follow the recommendations of Practice D4057, when obtaining
samples from bulk storage or pipelines. Samples that contain free layer of water will require special treatment. For the latter
samples, it may be necessary to separate and analyze the water and hydrocarbon phases separately. The water phase may be
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determined from a separate method. For such analysis, it is necessary to know the amount of water and hydrocarbon phases to
determine a total methanol content for the sample.
8.2 Prior to analysis, allow the sample container as received to equilibrate to ambient temperature.
9. Preparation of Apparatus and Establishment of Conditions
9.1 Determine Configuration—Refer to 4.2 to determine which configuration the chromatographic system is designed for the
analysis. For a valve configuration the dual detector Configuration B (Fig. 2) is recommended due to the fact that the system can
be assembled with no modifications to determine the cut times from the pre-column.
9.1.1 Figs. 1 and 2 are plumbing schematics for using a commercially available switching valve. This system is described
primarily in the following sections–Configurations A and B.
9.1.2 Figs. 3 and 4 are the plumbing schematics for using a commercially available fluidic switching system.
9.2 Configuration A (Single Detector Configuration):
9.2.1 Assembly—Refer to Fig. 1. First connect the polydimethylsiloxane pre-column (6.3.1) to the detector directly to set the cut
time (9.2.4) using low-volume connectors and inert narrow bore tubing. It is important to minimize the volume of the
chromatographic system that comes in contact with the sample; otherwise, peak broadening will occur.
9.2.2 Vent Restrictor—The vent restrictor is intended to simulate the restriction caused by the PLOT column on the pre-column.
This is needed to ensure accurate cut time determination while the valve is in the OFF position. A piece of stainless steel tubing,
70 cm in length, 0.16 cm O.D. and having 0.254 mm I.D., will approximate the column resistance.
9.2.3 Conditions—Establish the operating conditions listed in Table 2. This gives example conditions for the columns systems
used in the development of this method. With the pre-column connected to the FID directly, the inlet pressure should be adjusted
to ~31.0 kPa. This will set the column flow to approximately 6.8 mL ⁄min at 60 °C. This is necessary since there is no simulation
for the restriction caused by the PLOT column when the pre-column is installed directly to the FID. Modifications to column
lengths etc. may require different operating conditions. Check the system for leaks before proceeding further. Condition the system
overnight before proceeding.
9.2.4 Setting Valve Times—Once Configuration A is set up and the pre-column is connected to the detector, determine the retention
time of the oxygenates through the pre-column.
9.2.5 Inject 1 μL of a ~300 mg ⁄kg solution without ethanol or internal standard. To prepare this, add 20 μL of the solution made
in 10.3 to 5 mL of isooctane. Record the chromatogram, and identify the peaks for each oxygenate using Fig. 5. From this retention
time data, set the oxygenate transfer valve time ON to 0.5 min before the methanol starts eluting, and valve time OFF to 0.5 min
after the TAME peak returns to baseline. The times should be incorporated into the analysis method before calibration is begun.
9.2.6 Reassemble the system by reinstalling the PLOT column to the diagram in Fig. 1 and Table 2 using low-volume connectors
and inert narrow bore tubing. It is important to minimize the volume of the connections into and from the valve. Proceed to place
the Valve in the ON position so that the apolar column and PLOT column are in series. Inject the sample as described in 9.2.5 and
leave the valve in the ON position as determined in 9.2.5. Using the times determined in 9.2.5 transfer the oxygenates to the PLOT
column.
9.3 Configuration B (Dual Detector Configuration):
9.3.1 Assembly—For Configuration B, connect the WCOT and PLOT columns to the valve system as shown in Fig. 2 using
low-volume connectors and inert narrow bore tubing. It is important to minimize the volume of the chromatographic system that
comes in contact with the sample; otherwise, peak broadening will occur.
9.3.2 Vent Restrictor—The vent restrictor is intended to simulate the restriction caused by the PLOT column on the pre-column.
This is needed to ensure accurate cut time determination while the valve is in the OFF position (see Fig. 2). A piece of stainless
steel tubing, 70 cm in length, 0.16 cm O.D. and having 0.254 mm I.D., will approximate the column resistance.
D7754 − 23
9.3.3 Conditions—Establish the operating conditions listed in Table 2. This gives example conditions for the columns systems
used in the development of this test method. Modifications to column lengths etc. may require different operating conditions. Check
the system for leaks before proceeding further. Condition the system overnight before proceeding at an oven temperature of 200 °C.
9.3.4 Setting Valve Times—With the valve in the OFF position determine first the retention time of the oxygenates through the
apolar. Subsequently the same is repeated but with the valve in the ON position.
9.3.5 Switch the valve to the OFF position to monitor the pre-column only. Inject 1 μL of a ~300 mg ⁄kg solution without ethanol
or internal standard. To prepare this, add 20 μL of the solution made in 10.3 to 5 mL of isooctane. Record the chromatogram.
Identify the peaks for each oxygenate using Fig. 5. From this retention time data, set the oxygenate transfer valve time ON to
0.5 min before the methanol starts eluting, and valve time OFF to 0.5 min after the TAME peak returns to baseline. The times
should be incorporated into the analysis method before calibration is begun.
9.4 Configuration C (Single Detector Configuration Using a Fluidic Switch System:
9.4.1 The pre-column and the analytical column are linked by fluidic switch (CFT) purged union (see Fig. 3). The iInlet EPC
delivers 5.4 mL ⁄min to both columns. The AUX EPC delivers 1.6 mL ⁄min to the capillary flow technology (CFT) union. This
increases the flow to the analytical column to 7.0 mL ⁄min. Under these conditions the oxygenates are transferred in about 1.5 min.
9.4.2 High boiling point compounds are retained in the pre-column. Oxygenates and low boiling point hydrocarbons elute into
analytical column. Oxygenates are trapped at the front of the analytical column. After TAME has eluted to the analytical column,
the pre-column flow is reversed.
9.4.3 Inlet EPC flow is reduced to 4 mL ⁄min (Fig. 4) and AUX EPC flow is increased to 11 mL ⁄min. Gas flow through the fluidic
switch backflushes the pre-column in order to send high boiling compounds out the front inlet split vent. Oven temperature
program begins and oxygenates are separated on the analytical column. A typical chromatogram using this system is shown in Fig.
7.
9.5 Verification of Detectability—Inject a 5 mg ⁄kg calibration solution and ensure that a signal/noise level of at least 5 is observed.
Adjustment of the split ratio may be needed depending on the detector. See Fig. 8. The peaks for this level (5 mg ⁄kg) have a height
of about 2 pA.
9.6 Conditioning—To protect the PLOT column, avoid injecting samples until the valve times are properly optimized using
calibration standards. It is recommended that when all of the analyses are completed, the GC oven temperature be maintained at
220 °C, with the pre-column carrier head pressure maintained at 138 kPa using the electronic pressure controller for at least several
NOTE 1—Conditions in Table 2. Calibration Standard – mg/kg internal standard in isooctane.
FIG. 7 Oxygenate Elution Pattern from WCOT/PLOT Column Set Using the Fluidic Switch System
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