The Rapid Determination of Benzene and Toluene in Finished Gasolines Containing Ethanol Using Gas Chromatography - A. Tipler

The determination of benzene and toluene in gasoline is an important application in the petrochemical industry to monitor and ensure that levels of these compounds meet regulatory requirements.

Gasoline is a highly complex sample matrix and, in this instance, we want to just see the benzene and toluene content in among the hundreds of other components present. Traditionally, this analysis has been performed by gas chromatography using packed columns in a mechanical valve backflush configuration as described in ASTM method D3606-07. A non-polar precolumn allows the volatile fraction of an injected gasoline sample (which contains benzene and toluene) to elute into a second column which is polar. The heavier sample fraction, which was left in the precolumn, is removed by backflushing the precolumn out to vent. The polar analytical column retains the benzene and toluene more than the volatile hydrocarbons that also eluted into this column and so enables these aromatic compounds to be fully separated from all other components in the gasoline. A polar internal standard is added to the gasoline prior to analysis to improve the quantitative precision.

Such methods have been used for many years but the relatively recent introduction of high concentrations of ethanol in modern gasolines has caused peak-coelution issues on the polar analytical column. Alternative column sets have been developed to improve the chromatography but these have extended the analysis time.