ASTM D6293 Oxygenates and Paraffin, Olefin, Naphthene, Aromatic Hydrocarbon Types
ASTM D6293 Standard Test Method for Oxygenates and Paraffin, Olefin, Naphthene, Aromatic (O-PONA) Hydrocarbon Types in Low-Olefin Spark Ignition Engine Fuels by Gas Chromatography
7. Apparatus
7.1 The complete system that was used to obtain the precision data shown in Section 14 is comprised of a computer controlled gas chromatograph, automated sample injector, and specific hardware modifications. These modifications include columns, traps, a hydrogenator, and valves, which are described below and in Section 8. Fig. 1 illustrates a typical instrument configuration (see Note 8). Other configurations, components, or conditions may be utilized provided they are capable of achieving the required component separations and produce a precision that is equivalent, or better, than that shown in the precision tables.

7.2 Gas Chromatograph, capable of isothermal operation at specified temperatures, equipped with a heated flash vaporization inlet that can be packed (packed column inlet), a flame ionization detector, necessary flow controllers, and computer control.

7.3 Sample Introduction System, automatic liquid sampler, capable of injecting a 0.1 to 0.5-µL injection volume of liquid. The total injected sample shall 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.

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

7.5 Electronic Data Acquisition System, shall meet or exceed the following specifications (see Note 2):
7.5.1 Capacity for 150 peaks for each analysis.

7.5.2 Normalized area percent calculation with response factors.
7.5.2.1 Area summation of peaks that are split or of groups of components that elute at specific retention times.

7.5.3 Noise and spike rejection capability.

7.5.4 Sampling rate for fast (<0.5 s) peaks (>20 Hz to give 10 points across peak).

7.5.5 Peak width detection for narrow and broad peaks.

7.5.6 Perpendicular drop and tangent skimming, as required.

NOTE 2 - Standard supplied software is typically satisfactory.

7.6 Temperature Controllers of System Components - The independent temperature control of numerous columns and traps, the hydrogenation catalyst, column switching valves, and sample lines is required. All of the system components that contact the sample shall be heated to a temperature that will prevent condensation of any sample component. Table 1 lists the system components and operating temperatures (see Note 3). 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 shall have the capability of operating at temperatures ± 20°C of those indicated to accommodate specific systems. Temperature control may be by any means that will meet the requirements listed in Table 1.

NOTE 3 - The system components and temperatures listed in Table 1 and Section 8 are specific to the analyzer used to obtain the precision data shown in Section 14. Other columns and traps that can adequately perform the required separations are also satisfactory but may require different temperatures.

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

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

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

7.8 Valves, air, to control pressurized air for column and trap cooling. Automated valves are recommended.

NOTE 4 - New valves, tubing, catalyst, columns, traps, and other materials that contact the sample or gasses may require conditioning prior to operation in accordance with the manufacturer's recommendations.

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

8. Reagents and Materials
8.1 Air, compressed, < 10 mg/kg each of total hydrocarbons and H2O (Warning - see Note 5).

NOTE 5 - Warning: Compressed gas under high pressure that supports combustion.

8.2 Helium, 99.999 % pure, <0.1 mg/kg H2O (Warning - see Note 6).

NOTE 6 - Warning: Compressed gas under high pressure.

8.3 Hydrogen, 99.999 % pure, <0.1 mg/kg H2O (Warning - see Note 7).

NOTE 7 - Warning: Extremely flammable gas under high pressure.

8.4 Columns, Traps, and Hydrogenation Catalyst (System Components) - This test method requires the use of four columns, two traps, and a hydrogenation catalyst (see Note 3). Each system component is independently temperature controlled as described in 7.6 and Table 1. Refer to Fig. 1 for the location of the components in the system (see Note 8). The following list of components contains guidelines that are to be used to judge suitability.

NOTE 8 - Fig. 1 shows an additional trap, Molsieve 5A, and rotary valve V4 that are not required for the O-PONA analysis. They are included in Fig. 1 because they were present in the instrumentation used to generate the precision data. They can be used for more detailed analyses outside the scope of this test method, where an iso-normal paraffin, iso- normal olefin determination is desired. There is no statistical data included in this test method relating to their use.

8.4.1 Alcohol Trap - Within a temperature range from 140 to 160°C, this trap must elute benzene, toluene, all paraffins, olefins, naphthenes, and ethers within the first 2 min after sample injection while retaining C8+ aromatics, all alcohols, and any other sample components.
8.4.1.1 At a temperature of 280°C, all retained components from 8.4.1 shall elute within 2 min of when the trap is backflushed.

8.4.2 Polar Column - At a temperature of 130°C, this column must retain all aromatic components in the sample longer than the time required to elute all non-aromatic components boiling below 185°C, within the first 5 min after sample injection.
8.4.2.1 The column shall elute benzene and toluene within 10 min of the introduction of these compounds into the column.

8.4.2.2 This column shall elute all retained aromatic components from 8.4.2 within 10 min of when this column is backflushed.

8.4.3 Non-Polar Column - At a temperature of 130°C, this column shall elute and separate aromatics by carbon number boiling below 200°C. Higher boiling paraffins, naphthenes, and aromatics are backflushed.

8.4.4 Olefin Trap - Within a temperature range from 120 to 170°C, this trap shall retain (trap) all olefins in the sample for at least 10 min and elute all non-olefinic components in less than 10 min after the sample is injected.
8.4.4.1 At a temperature of 280°C, this trap shall quantitatively elute all retained olefins.

8.4.5 Molsieve 13X Column - This column shall separate paraffin and naphthene hydrocarbons by carbon number when temperature programmed from 90 to 430°C at approximately 10°/minute.

8.4.6 Porapak Column - At a temperature from 130 to 140°C, this column shall separate individual oxygenates, benzene, and toluene.

8.4.7 Ether-Alcohol-Aromatic (EAA) Trap - Within a temperature range from 130 to 140°C, this trap shall retain all of the ethers in the sample and elute all non-ethers boiling above 174°C within the first 6 min after sample injection.
8.4.7.1 At a temperature of 280°C, this trap shall elute all retained components.

8.4.8 Hydrogenation Catalyst, platinum. At a temperature of 180°C and an auxiliary hydrogen flow of 14 ± 2 mL/min, this catalyst shall quantitatively hydrogenate all olefins to paraffinic compounds of the same structure without cracking.

8.5 Test Mixtures - Three quantitative synthetic mixtures of pure hydrocarbons and oxygenates 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 mixtures may be purchased or prepared according to Practice D4307. Each component used in the test mixture preparations shall have a minimum purity of 99 %. The actual concentration levels are not critical but shall be accurately known.
8.5.1 System Validation Test Mixture, used to monitor and make adjustments to the total operation of the system. The composition and approximate component concentrations are shown in Table 2.

8.5.2 Olefin Test Mixture, used to adjust the olefin and EAA trap temperatures so that C5 through C9 olefins are quantitatively determined. The composition and approximate component concentrations are shown in Table 3.

8.5.3 Paraffin Test Mixture, used to adjust the olefin and EAA trap temperatures. The composition and approximate component concentrations are shown in Table 4.

NOTE 9 - Warning: Extremely flammable. Harmful if inhaled.

NOTE 10 - Warning: Flammable. Harmful if inhaled.

NOTE 11 - Warning: Harmful if inhaled.

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