Sunday, March 18, 2012

Benzene and Toluene in Gasoline

I recently did an analytical Chemistry Experiment in which a local gasoline sample was characterized using Gas Chromatography/Mass Spectrometry and Gas Chromatography by flame ionization detector. Benzene is naturally present in gasoline, and is classifed as a class 3 transportation hazard by the Environmental Protection Agency1 because it is toxic and carcinogenic. Looking at the results of previous years of the same lab experiment, the concentration of benzene in gasoline in volume percent has declined from 4% from 5 years ago to 1% in 2012, due to EPA regulations that the benzene content in gasoline must not exceed 1.03%. Below are the relevant results:

Figure 1: Selective ion chromatogram of gas sample showing benzene and toluene peaks.

The benzene peak is the top peak in the GC chromatogram, and the bottom peak is toluene (also present in gasoline and a possible carcinogen), which was used an internal standard. This experiment confirms that petroleum overusage is not only bad for our planet, it is also bad for our health. The bright side is that it is getting curbed by the EPA. The national average benzene content in gasoline is 0.62%, which is a very optimistic number2.

As a last note, consider that gasoline is composed of many different hydrocarbons, and as of 2011 benzene is considered a carcinogen while toluene is still relatively under the radar with little scientific data about the extent of its carcinogenic capacity. As we continue to burn gasoline, we may be experiencing long term subtle effects to our health that we are not yet aware of. Below is the total ion chromatogram of gasoline.
 
Figure 2: GCMS total ion chromatogram of gasoline sample showing all the hydrocarbon peaks.

The selective ion chromatograms for benzene and toluene from figure 1 were extracted from this total ion chromatogram in figure 2. As we can see, gasoline contains many other hydrocarbons whose effects on our health have not yet been studied.

REFERENCES:

1.      Instrumental Analysis Web Notes. Air Quality: GC/MS Analysis of Benzene in Gasoline and GCFID Determination of Toluene in Air. Winter 2012. Last Revised January 13, 2012.
2.      United States Environmental Protection Agency. http://www.epa.gov/otaq/regs/toxics/420f07017.htm. Control of Hazardous Air Pollutants from Mobile Sources: Fianl Rule to Reduce Mobile Source Air Toxics. Office of Transportation and Air Quality (OTAQ). March 11, 2012



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