ASTM D4420 Determination of Aromatics in Finished Gasoline by Gas Chromatography
5. Apparatus
5.1 Chromatograph - Any chromatographic instrument that has a direct vaporizing injector, backflush system, and a thermal conductivity detector, and that can be operated at the conditions given in Table 1, can be employed. Two backflush systems are shown. Fig. 1 is a flow diagram employing an eight port rotary valve, and Fig. 2 is a flow diagram using an eleven port linear valve. Either flow pattern may be used.
5.1.1 Thermal Conductivity Detector - Either one dual-filament or two single-filament detectors can be used. With dual-filament detectors, both the analytical side and the reference side are used separately to detect eluting components. Proper detection is achieved by manual or automatic switching of the signal polarity. Newer gas chromatographs equipped with single-filament detectors usually have the capability to automatically switch from one signal output to the other so that they also require only a single recorder or single channel of integration.

5.1.2 Sensitivity - An overall sensitivity sufficient to detect 0.1 volume % of benzene with a peak height of at least 3-mm with a 3-µL injection.

5.2 Recorder, strip chart. A0 to 1-mV range recording potentiometer with a response time of 2 s or less and a maximum noise level of +/- 0.3 % of full scale.

5.3 Integrator, computer or electronic integration.

5.4 Column - Two columns, as described in Table 2. Column A (polar) separates aromatics from nonaromatics and Column B (nonpolar) separates the aromatics by carbon number.

5.5 Microsyringe, 5-µL capacity.

6. Reagents and Materials
6.1 Carrier Gas, helium, 99.99 % pure. (Warning - Compressed gas under high pressure.)

6.2 Solid Support, crushed firebrick or inert diatomaceous earth, acid-washed, 60 - 80 mesh.

6.3 Liquid phases, OV-2755 and methyl silicone.

6.4 Isooctane, 99+ mol %. (Warning - Extremely flammable. Harmful if inhaled.)

6.5 Benzene, 99+ mol %. (Warning - Poison. Carcinogen. Harmful or fatal if swallowed. Extremely flammable. Vapors may cause flash fires.)

6.6 Toluene, 99+ mol %. (Warning - Flammable. Vapor harmful.)

6.7 Xylenes, mixed, reagent grade, (Warning - Flammable. Vapor harmful.) Contains ethylbenzene. (Warning - Flammable. Vapor harmful.)

6.8 n-Butylbenzene, 99+ mol %. (Warning - Flammable. Vapor harmful.)