Benzene is used as an additive into gasoline to increase octane rating and prevent engine knocking. Being a toxic air pollutant known to have carcinogenic effects, knowledge of its concentration, determined by gas chromatography,can aid in the assessment of possible health hazards to persons handling and using gasoline. The U.S. Federal Clean Air Act and the European Community specifications mandate a level of benzene in gasoline below 1% in volume. To meet the specific limits of benzene, an accurate quantitative determination of the compound is essential.
The ASTM D3606 method is designed to determine benzene and toluene content in motor and aviation gasoline using packed columns and a thermal conductivity detector (TCD). The following gas chromatography (GC) methodology describes the determination of these components in gasoline, using the Thermo Scientific TRACE 1310 GC in a split/splitless-backflush configuration using capillary columns and flame ionization detection (FID), for a simpler fully automated analysis. The SSL/backflush injector used in this paper is a user-installable, compact and self-sufficient module featuring all the required hardware components and the electronic carrier gas controls.
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Seven standard samples were used to build the calibration curve. They cover a 0.06 to 5% volume concentration range for benzene and a 0.5 to 20% volume concentration range for toluene. The calibration curve is linear with a R2 of 0.999 for both compounds. Then a common retail gasoline sample with no alcohol content was analyzed. The average content in benzene was 0.57% in volume and 5.84% in volume in toluene. To validate the system robustness, a total of 170 runs of the gasoline samples were performed in this study. The repeatability was tested on 150 samples following the ASTM method specifications. The total area RSD% was 1.21 for benzene and 1.26 for toluene confirming exceptional system stability. Two samples out of 150 exceeded the repeatability calculated values, respectively 0.027 and 0.195 for benzene and toluene. This is well within the ASTM limit of one case in twenty being higher than the repeatability calculated values. The reproducibility, as stated in the ASTM method, was tested on a second system running 20 samples. No value outside the reproducibility test range values, respectively 0.12 and 0.77 for benzene and toluene, was observed. Both repeatability and reproducibility exceeded the requirements of the ASTM D3606 method.
In this application, we show the possibility to perform gasoline analysis with excellent repeatability and reproducibility using the TRACE 1310 gas chromatograph. Adopting an FID detector and capillary columns, this solution eliminates the need for a dedicated instrument or expensive packed column sets.
Download application note here: Application Note 52284: Simplification of the ASTM D3606 Method for the Determination of Benzene and Toluene in Gasoline