ASTM D4420 Determination of Aromatics in Finished Gasoline by Gas Chromatography
10. Procedure
10.1 Chromatographic Analysis - Chromatograph the sample using the procedure described for the calibration mixture in 9.2. The volume of sample injected must be exactly the same as the volume used for calibration.
10.1.1 A sample that contains heavy non-aromatics, which interfere with the determination of C9 + aromatics, is indicated on the chromatogram by the non-aromatics reverse peak not returning to near-baseline by time T1. If a single-filament detector is being used, the nonaromatics peak will appear positive. For quantitation of the C9 + aromatics composite, times T1a and T2a are determined and utilized for a second analysis of this same sample that determines C9 + aromatics only.
10.1.2 Time T1a is determined by chromatographing the calibration blend with the valve in forward flow position and the detector on polarity "B". If a single-filament detector is being used, monitor the signal from Detector B. Determine the time in seconds at which the mixed xylenes composite begins to elute and subtract 6 s from this value. Call this time T1a.
10.1.3 Chromatograph the blend with the detector on polarity A. If a single-filament detector is being used, monitor the signal from Detector A. At time T1a, switch the valve to the backflush position. When the o-xylene peak returns to baseline, switch the valve to the forward flow position. Call this time T2a. This is illustrated in Fig. 5.
10.1.4 If the non-aromatics peak for the sample containing heavy non-aromatics returns to a near baseline condition before time T1a, the C9 + aromatic composite can be determined from this second analysis. If a near-baseline condition is still not achieved, the C9 + aromatics composite cannot be determined.
10.2 Measurement of Area - Measure the areas of the benzene, toluene, C8 aromatics composite and C9 + composite. Units must be consistent with 9.2.3 above.
NOTE 5 - The precision statement in Section 13 was developed from data obtained using electronic integrators or on-line computers. The precision statement need not apply if other methods of integration or peak area measurement is used.
11. Calculation
11.1 Calculate the liquid volume percent (LV-%) of each aromatic hydrocarbon component or group present in the sample using the following equation:
Component, LV - % = FC
where:
F = response factor, previously defined in 9.2.3 and
C = peak area for that component
