ASTM-D5580:15(R2020) pdf free download – Standard Test Method for Determination of Benzene, Toluene, Ethylbenzene, p/m- Xylene, o-Xylene, Cg and Heavier Aromatics, and Total Aromatics in Finished Gasoline by Gas Chromatography.
6. 1 . 1 Gas Chromatograph (GC), capable of operating at the conditions given in Table I, and having a column switching and backilushing system equivalent to Fig. 1. Carrier gas pressure and flow control devices shall be capable of precise control when column head pressures and flow rates are low.
6. 1 .2 Sample Introduction System, capable of introducing a representative sample into the gas chromatographic inlet. Microlitre syringes and automatic syringe injectors have been used successfully.
6. 1 .3 Inlet System, (splitting tvpe)—Split injection is necessary to maintain the actual chromatographed sample size within the limits required for optimum column efficiency and detector linearity.
6.1.3.1 Some gas chromatographs are equipped with on- column injectors and autosamplers which can inject submicrolitre sample sizes. Such systems can be used provided that column efficiency and detector linearity are comparable to systems with split injection.
6.1.4 Detector—A flame ionization detector (Detector A) is employed for quantitation of components cluting from the WCOT column. The flame ionization detector used for Detector A shall have sufficient sensitivity and stability to detect 0.01 % by volume of an aromatic compound.
6.1.4.1 It is strongly recommended that a thermal conductivity detector be placed on the vent of the TCEP precolumn (Detector B). This facilitates the determination of valve BACKFLUSH and RESET times (10.5) and is useful for monitoring the separation of the polar TCEP precolurnn.
6. 1 .5 Swiichini aiitl Backflushing Vah’e, to he located within a temperature-controlled heated zone and capable of performing the functions in accordance with Section 10, and illustrated in Fig. 1. The valve shall he of low internalvolume design and not contribute significantly to deterioration of chromatographic resolution.
6.1.5.1 A 10-port valve with 1.6 mm (0.06 in.) outside diameter fittings is recommended for this test method. Alternatively, and if using columns of 0.32 mm inside diameter or smaller, a valve with 0.8 mm (0.03 in.) outside diameter fittings should be used.
6.1.5.2 Some gas chromatographs are equipped with an auxiliary oven which can be used to contain the valve. In such a configuration, the valve can be kept at a higher temperature than the polar and nonpolar columns to prevent sample condensation and peak broadening. The columns are then located in the main oven and the temperature can he adjusted for optimum aromatic resolution.
6.1.5.3 An automatic valve switching device is strongly recommended to ensure repeatable switching times.
6.2 Data Acquisition Svstein.
6.2.1 Integrator or Compurer capable of providing realtime graphic and digital presentation of the chromatographic data are recommended for use. Peak areas and retention times can he measured by computer or electronic integration.
6.2.1.1 It is recommended that this device be capable of performing multilevel internal-standard-type calibrations and be able to calculate the correlation coefficient (ri and linear least square fit equation for each calibration data set in accordance with 11 .4.
6.3 chroinaw graphic Columns (two columns are used):
6.3.1 Polar Precolunin, to perform a pre-separation of the aromatics from nonaromatic hydrocarbons in the same boiling point range. Any column with equivalent or better chromatographic efficiency and selectivity in accordance with 6.3.1 .1 can be used.