Leonard M Sidisky, Gustavo Serrano Izaquirre, Michael D Buchanan
Reporter US, Volume 33.4
The amount of benzene in gasoline is a concern because it is a known human carcinogen, and exposure to it has been linked to detrimental health effects. The challenge with the analysis lies in the complex composition of gasoline, which consists of hundreds of different compounds. Reformulated gasoline also contains additives to produce more complete combustion and subsequent lower emissions of harmful compounds. These additives accomplish this by boosting the oxygen content, and are commonly referred to as “oxygenates”. Ethanol is a commonly used oxygenate. Therefore, to measure benzene in reformulated gasoline, it must be resolved from the aliphatic hydrocarbons, other aromatics, ethanol, plus any other oxygenates. This typically requires the use of a two-column switching procedure.1
We developed SLB®-ILD3606, a capillary gas chromatography (GC) column engineered for the determination of benzene (and other aromatics) and oxygenates in gasoline. Table 1 lists its specifications. It is a modified (inert) version of SLB-IL111, a GC column that employs an imidazolium dicationic ionic liquid stationary phase. This new column provides the unique selectivity of the extremely polar SLB-IL111, but with improved peak shapes for oxygenates, resulting in improved resolution for all analytes.
To show selectivity and inertness capabilities, a mixture containing two aromatics, five alcohols, and one ketone was prepared in isooctane following the guidelines for a control standard to be used with ASTM® D3606. This mix was analyzed using temperature programming, and the resulting chromatogram is shown in Figure 1. The inertness of the column resulted in sharp peak shapes for all alcohols, which in turn resulted in great resolution between ethanol and benzene (RS=12.6), and also between iso-butanol and toluene (RS = 5.6).
Figure 1. Aromatic and alcohol standard.
Figure 2 shows the chromatogram resulting from the analysis of a reformulated gasoline sample on SLB®-ILD3606. As shown:
These observations indicate the SLB®-ILD3606 is an effective alternative to the two-column switching procedure currently required for the determination of benzene and other aromatics in reformulated gasoline.
Figure 2. Reformulated gasoline.
The measurement of benzene and oxygenate compounds in reformulated gasoline is a common application performed worldwide, both in on-site labs at industrial facilities and also in third-party testing labs. As shown, the SLB®-ILD3606 column is able to resolve both benzene and toluene from oxygenates (such as alcohols, ketones, and ethers) and also the aliphatic portion of gasoline in a one-column set-up.
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