ASTM D6296 Standard Test Method for Total Olefins in Spark-ignition Engine Fuels
ASTM D6296 Standard Test Method for Total Olefins in Spark-ignition Engine Fuels by Multi-dimensional Gas Chromatography
7. Apparatus
7.1 The complete system used to obtain the precision data is comprised of a computer controlled gas chromatograph, automated sample injector, computer software, and specific hardware modifications. These modifications include columns, traps, and valves which are described as follows and in Section 8. Fig. 1 illustrates a typical flow diagram and component configuration. Other configurations, components, or conditions may be utilized provided they are capable of separating the olefins and producing a precision that is equivalent, or better, than that shown in the table of precision data.

7.2 Gas Chromatograph, dual column, temperature programmable over a range from 60 to 160°C at approximately 20°C/min, equipped with heated flash vaporization sample inlets, a single flame ionization detector, necessary flow controllers, and computer control.

7.3 Sample Introduction System, manual or automatic, capable of injecting a reproducible 0.2-µL injection volume of liquid. The total injected sample must be introduced to the chromatographic system, thus excluding the use of split injections or carrier gas purging of the inlet septum. An auto injector is recommended but optional. The precision data was obtained using an automated sample injector.

7.4 Gas Flow and Pressure Controllers, with adequate precision to provide reproducible flow and pressure of helium to the chromatographic system, and hydrogen and air for the flame ionization detector. Control of air flow for rapid cooling of specific system components and for automated valve operation is also required.

7.5 Electronic Data Acquisition System, must meet or exceed the following specifications (see Note 3):
7.5.1 Capacity for 150 peaks for each analysis,

7.5.2 External standard calculation of selected peaks with response factors and background correction,

7.5.3 Noise and spike rejection capability,

7.5.4 Sampling rate for fast (<4.0 s.) peaks (>5 Hz to give 20 points across peak),

7.5.5 Peak width detection for narrow and broad peaks, and

7.5.6 Perpendicular drop.

NOTE 3 - Standard supplied software is typically satisfactory.

7.6 Gas Purifiers, to remove moisture and oxygen from helium, moisture and hydrocarbons from hydrogen, and moisture and hydrocarbons from air.

7.7 Balance, analytical, capable of weighing 0.0001 g.

7.8 Glassware:
7.8.1 Vial, autosampler, with caps and including a cap crimper (required when the recommended optional autosampler is used).

7.8.2 Pipette, Pasteur, disposable, with bulb.

7.8.3 Pipette, volumetric, graduated in 0.01 mL increments, 1- and 2-mL capacity.

7.8.4 Pipette, total volume, 1, 3, 5, 10, 20 and 25-mL capacity.

7.9 Septa, polytetrafluoroethylene (PTFE) lined for injector.

7.10 Temperature Controllers of System Components - The independent temperature control of two columns and two traps, column switching valves, and sample lines is required. All system components that contact the sample must be heated to a temperature that will prevent condensation of any sample component. Table 1 lists the system components and operating temperature (see Note 4). Some of the components require isothermal operation, some require rapid heating and cooling, while one requires reproducible temperature programming. The indicated temperatures are typical; however, the control systems utilized must have the capability of operating at temperatures +/- 20° of those indicated to accommodate specific systems. Temperature control may be by any means that will meet the requirements of Table 1.

NOTE 4 - The system components and temperatures listed in Table 1 and Section 8 are specific to the analyzer used to obtain the precision data. Other columns and traps that can adequately perform the required separations are also satisfactory but may require different temperatures.

7.11 Valves, Column, and Trap Switching - automated 6-port rotary valves are recommended. The valves must be intended for gas chromatographic usage and meet the following requirements:
7.11.1 The valves must be capable of continuous operation at operating temperatures that will prevent sample condensation.

7.11.2 The valves must be constructed of materials that are non-reactive with the sample under analysis conditions. Stainless steel, PFA, and Vespel6 are satisfactory.

7.11.3 The valves must have a small internal volume but offer little restriction to carrier gas flow under analysis conditions.

7.12 Valves, Air, to control pressurized air for ether/alcohol and olefin trap cooling; 3-port automated valves are recommended.

NOTE 5 - New valves, tubing, columns, traps, and other materials that contact the sample or gasses may require conditioning prior to operation in accordance with the manufacturer's instructions.

8. Reagents and Materials
8.1 Air, compressed, <10 mg/kg each of total hydrocarbons and H2O. (Warning - See Note 6.)

NOTE 6 - Warning: Compressed gas under high pressure that supports combustion.

8.2 Helium, 99.999 % pure, <0.1 mg/kg H2O (Warning - See Note 7.)

NOTE 7 - Warning: Compressed gas under high pressure.

8.3 Hydrogen, 99.999 % pure, <0.1 mg/kg H2O (Warning - See Note 8.)

NOTE 8 - Warning: Extremely flammable gas under high pressure.

8.4 2,2,4-trimethylpenane (isooctane), 99.99 % pure (Warning - See Note 9.)

NOTE 9 - Warning: Flammable. Harmful if inhaled.

8.5 Columns and Traps (System Components) - This test method requires the use of two chromatographic columns and two traps (see Note 4). Each system component is independently temperature controlled as described in 7.10 and Table 1. Refer to Fig. 1 for the location of the components in the system. The following list of columns and traps contains guidelines that are to be used to judge suitability.
8.5.1 Polar Column - At a temperature of 160°C, this column must retain all aromatic components in the sample and elute all non-aromatic components boiling below 200°C, which includes decene and lower boiling olefins, within 2 min after sample injection.
8.5.1.1 This column must elute all aromatics and other components retained from 8.5.1 within 8 min of when it is backflushed.

8.5.2 Ether/Alcohol Trap - At a temperature of 140°C, this trap must retain alcohols and ethers and elute all non-oxygenates boiling below 200°C within 4.5 to 5.0 min after sample injection.
8.5.2.1 At a temperature of 280°C, this trap must elute all retained components.

8.5.3 Olefin Trap - Within a temperature range from 140 to 165°C, this trap must quantitatively retain (trap) all olefins in the C4 to C10 range for at least 10 min after sample injection while eluting all non-olefin components boiling below 200°C.
8.5.3.1 At a temperature of 280°C, this trap must quantitatively elute all trapped olefins.

8.5.4 Non-Polar Column - At a temperature of 160°C, this column must elute paraffins and naphthenes through C11 within 2 min.
8.5.4.1 This column must distribute the C4 through C10 olefins by carbon number when temperature programmed from 60 to 160°C at approximately 20°C/min.

8.6 Set Up Mixtures - Two qualitative synthetic mixtures containing isooctane and ethers are required to verify that all instrument components, temperatures, and cut times are satisfactory to produce accurate analyses and to aid in making operating adjustments as columns and traps age. The composition of these mixtures and approximate component concentrations are shown in Table 2. The mixtures may be purchased or prepared according to Practice D4307. (Warning - See Note 9.)

8.7 Calibration Standards - Quantitative synthetic mixtures of pure hydrocarbons and ethers (Warning - See Note 9) are required to verify that the required component separation is being achieved, to determine the retention time of the olefins by carbon number, and to determine the response factor on the FID for the olefins. Examples of two mixtures, including densities of individual components, are shown in Table 3 and Table 4. Calibration Standard 1 is used for all samples except those that contain ETBE and Calibration Standard 2 is used for samples containing ETBE. When the oxygenate composition of samples is unknown, it can be determined using Test Method D4815, D5599, or other test methods. Mixtures may be purchased or prepared according to Practice D4307. The actual concentration levels are not critical but must be accurately known. Determine the density of the calibration standard by Test Method D4052 or other test method.

8.8 Quality Control Sample, used to routinely monitor the operation of the chromatographic system and to verify that reported concentrations are within the precision of the test method. A sample or samples that are similar in composition to samples typically analyzed may be designated as the quality control (QC) samples. When samples to be analyzed contain C4 and C5 olefins, the QC samples must contain these to monitor olefin trap capacity. Each QC sample must be of sufficient volume to provide an ample supply for the intended period of use, and it must be homogeneous and stable under the anticipated storage conditions.