ASTM D 3606 17

Keep your benzene in check with ASTM D3606

 

While benzene historically has been used as an additive in gasoline and aviation fuel, it is a known toxic air pollutant and is regulated by both the EPA and European Union. While the ASTM has published both capillary and packed column methods this blog will focus purely on the more robust packed approach. With the addition of ethanol to gasoline modifications have been made to the method to prevent the coelution of benzene / ethanol which allows for the quantification of benzene at concentrations ranging from 0.1% to 5% by volume. Toluene, while less toxic, can be quantified at between 2% and 20% by volume.

 

Since benzene and ethanol are poorly resolved on some column configurations, we have found a solution using a two column set. Column #1 is a 6’ x 1/8” OD (1.8m x 2mm id) nonpolar Rtx-1 polymer, which separates components in boiling point order. After the elution of n-octane (C8), column #1 is back flushed to prevent the heavier compounds from entering column #2, the main analytical column.  Column #2 a 16’ x 1/8” OD (4.9m x 2mm id) column packed with a proprietary polymer that allows complete resolution of ethanol/benzene, R = > 1.50. One thing to remember; if the column set is housed in an auxiliary oven, manually check the oven temperature to be sure it is actually at the method temperature of 135°C.  An incorrect oven temperature can result in poor resolution. If you suspect your oven is not at the correct temperature check the retention time of toluene. One of the most important, yet commonly overlooked problems is oxygen and moisture in the chromatographic system. Regardless of what GC system you’re using always have oxygen and moisture filters installed on the carrier gas line as close to the GC as possible to assure a trouble-free analysis.

 

Stay tuned for more blogs on this topic

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