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
9. Preparation of Apparatus
9.1 Assemble the analyzer system (gas chromatograph with independent temperature controlled components) as shown in Fig. 1 or with an equivalent flow system. If using a commercial system, install and place the system in service in accordance with the manufacturer's instructions.
9.2 Impurities in the helium carrier gas, hydrogen, or air will have a detrimental effect on the performance of the columns and traps. Therefore, it is important to install efficient gas purifiers in the gas lines as close to the system as possible and to use good quality gases. The helium and hydrogen gas connection lines shall be made of metal. Check that all gas connections, both exterior and interior to the system, are leak tight.
9.3 The gas flow rates on commercial instruments are normally set prior to shipment and normally require little adjustment. Optimize flow rates on other systems to achieve the required separations. Typical flow rates for the commercial instrument used in the precision study are given in Table 5; however, the flows can differ somewhat from system to system.
9.3.1 Set air flow rates for column/trap cooling and for operation of air actuated valves, if required.
9.4 System Conditioning - When gas connections have been disconnected or the flow turned off, as on initial start up, condition the system by permitting carrier gas to flow through the system for at least 30 min while the system is at ambient temperature. After the system has been conditioned, analyze the system validation test mixture, as described in 11, discarding the results.
10. Standardization
10.1 The elution of components from the columns and traps depends on the applied temperatures. The switching valves also need to be actuated at exact times to make separations of compounds into groups, for example, to retain specific compounds in a column or trap while permitting other compounds to elute. Therefore, the separation temperatures of the columns/traps and the valve timing are critical for correct operation of the system. These parameters need to be verified on the start up of a new system (see Note 12) for correctness. They also require evaluation and adjustment as necessary on a regular basis to correct for changes to columns and traps as a result of aging. To do this, the analyst shall analyze several test mixtures and make changes, as required, based on an evaluation of the resulting chromatograms and test reports.
10.2 Using the procedure outlined in Section 11, analyze the system validation test mixture. Carefully examine the chromatogram obtained to verify that all the individual components of the test mixture are correctly identified as compared to the reference chromatogram (Figs. 2 and 3). Test results for group totals shall agree with the known composition (see Table 2) within ± 0.5 mass %. If these specifications are met, proceed to the analysis of the olefin test mixture (see 10.3).
10.2.1 If the specifications in 10.2 are not met, adjust the temperature of specific columns and traps or valve timing according to the manufacturer's guidelines and reanalyze the system validation test mixture until they are met.
10.3 Analyze the olefin test mixture and compare the results obtained to the actual values, Table 3. If the results do not agree within ± 0.3 mass % for the individual C5 through C8 olefins and ± 0.5 mass % for 1-nonene, adjust the temperatures of the olefin and EAA traps to ensure that the five olefins are retained on the olefin trap and not on the EAA trap. Reanalyze the olefin test mixture until specifications are met.
10.4 Analyze the paraffin test mixture and compare the results obtained to the actual values, Table 4. Ensure that <0.05 mass % of the nonane is retained by the olefin trap. Some or all of the decane may be retained by the olefin trap. If necessary, adjust the temperatures of the olefin and EAA traps. Reanalyze the paraffin test mixture until the specification for nonane is met.
10.5 Analyze the quality control sample, see 8.6. Verify that results are consistent with those previously obtained and that there is no breakthrough of olefins into the saturates region of the chromatogram. Breakthrough is indicated by a rising baseline under the C5 - C6 saturates region. If breakthrough is observed, optimize the olefin trap temperature or, if necessary, replace the trap. Loadability limits are as shown in 1.2. These limits depend on the condition of the olefin trap, and an aged trap may not have this capacity. Use the quality control sample, see 8.6, to verify olefin capacity.
10.6 Reanalyze the system validation test mixture whenever the quality control sample does not conform to expected results, see 10.5, and make adjustments as necessary, see 10.2.
