ASTM D6729 Method for Individual Components in Spark Ignition Engine Fuels
ASTM D6729 Standard Test Method for Determination of Individual Components in Spark Ignition Engine Fuels by 100 Metre Capillary High Resolution Gas Chromatography
6. Apparatus
6.1 Gas Chromatograph, a gas chromatograph equipped with cryogenic column oven cooling and capable of producing repeatable oven ramps from 0° to at least 300°C is required. The following features are useful during the sample analysis phase: electronic flow readout, electronic sample split-ratio readout, and electronic pneumatic control of flow. Though their use is not required, careful review of this test method will demonstrate the usefulness of a gas chromatograph equipped with these features. These features will replace the need to carry out the manual calculations that must be performed as listed in 8.1 and 8.2.
6.2 Inlet - a capillary split/splitless inlet system operated in the split mode is recommended. It must be operated in its linear range. Refer to 8.4 to determine the proper split ratio.
6.2.1 Carrier Gas Pneumatic Control - Constant carrier gas pressure control was used by all cooperative study participants. This may be either direct pressure to the inlet (injector) or by sing a total flow/back pressure system.
6.2.2 Pneumatic Operation of the Chromatograph - The use of constant pressure was the mode of operating the gas chromatography used by the participants in the interlaboratory cooperative study. Other carrier gas control methods such as constant flow (pressure programming) may be used, but this may change the chromatography elution pattern unless the temperature programming profile is also adjusted to compensate for the flow differences.
6.2.3 Temperature Control - The injector operated in the split mode shall be heated by a separate heating zone and heated to temperatures of 200 to 275°C.
6.3 Column, a fused silica capillary column, 100 m in length by 0.25 mm inside diameter, coated with a 0.5 mm film of bonded dimethylpolysiloxane. The column must meet the resolution requirements expressed in 8.3. Columns from two different commercial sources were used in the interlaboratory cooperative study.
6.4 Data System, a computer based chromatography data system capable of accurately and repeatedly measuring the retention time and areas of eluting peaks. The system shall be able to acquire data at a rate of at least 10 Hz. Although it is not mandatory, a data system which calculates column resolution (R) is extremely useful as it will replace the need to carry out the manual calculations which must be performed as listed in 8.3.
6.4.1 Electronic Integrators, shall be capable of storing up to 400 components in the peak table and shall be able to acquire the data at 10 Hz or faster speeds. They shall be capable of integrating peaks having peak widths at half height which are 1.0s wide. The integrator must be capable of displaying the integration mode of partially resolved peaks. In addition, these integrators should be able to download a commonly readable format of data (that is, ASCII) to a computer in order to facilitate data processing.
6.5 Sample Introduction - Sample introduction by way of a valve, automatic injection device, robotic arm or other automatic means is highly recommended. An automatic sample introduction device is essential to the reproducibility of the analysis. Manual injections are not recommended. All of the reproducibility data reported by this test method for the samples analyzed were gathered using automatic injection devices.
6.6 Flame Ionization Detector (FID) - The gas chromatograph should possess a FID having a sensitivity of 0.005 coulombs/g for n-butane. The linear dynamic range of the detector should be 106 or better. The detector is heated to 300°C.
7. Reagents and Materials
7.1 Calibrating Standard Mixture - A spark ignition engine fuel standard of known composition and concentration by mass can be used. In order to corroborate the identification of the sample, a typical chromatogram (Fig. 1) was obtained from reference sample ARC96OX.
7.2 Gas Chromatograph Gases - All of the following gases shall have a purity of 99.999 % (V/V) or greater.
NOTE 1 - Warning: Gases are compressed. Some are flammable and all gases are under high pressure.
7.2.1 Helium - The test data was developed with helium as the carrier gas. It is possible that other carrier gases may be used for this test method. At this time, no data is available from this test method with other carrier gases.
7.2.2 Air, Hydrogen and Make-up Gas (Helium or Nitrogen), shall have a purity of 99.999 % (V/V) or greater.
