Ethanol has been used in internal
combustion engines on an intermittent basis for the past century. It is
obtained from the fermentation of starchy plant material, most often corn in
the United States. Approximately 2.5
gallons of ethanol can be collected from 1 bushel of corn. Although a perfectly good fuel, the
relatively high cost of producing ethanol has prevented its widespread use
except during petroleum shortages. Some
countries without petroleum resources, however, use it extensively.
In the United States, the addition
of ethanol to gasoline (gasohol) gained interest during the oil crises in the
1970’s. Subsidies were initiated to
encourage ethanol production and the manufacturing of gasohol. These subsidies allow gasohol, which is more
expensive to make, to compete with straight gasoline at the pump. As with all
farm subsidies, however, gasohol subsidies are controversial. Many farmers in Illinois, of course, benefit
from the subsidies, and would like to see the program continue.
The environmental effects of the use
of gasohol vs. gasoline are mixed. On
the one hand, gasohol usually burns more completely than gasoline (can you
think of why?), thus reducing atmospheric contamination. On the other hand, the vapor pressure of
gasohol is greater than gasoline, so gasohol evaporates more readily which
increases atmospheric contamination (especially in warm weather). Some communities require the use of an
oxygenated fuel like gasohol during the winter months, particularly if
atmospheric inversions are common.
Your assignment is to use GC and
HPLC to quantify the amount of ethanol in a gasohol sample. Gasohol is a very
complex mixture, so you’ll probably need to spend some time determining an
effective chromatographic method. In
GC, this might entail temperature programming.
In HPLC, a suitable mobile phase mixture might be needed or a gradient
elution method used.
Whichever technique you choose, one requirement of
the lab is that you use an internal standard for your quantitative analysis.
Some
other things to consider:
Solvent
choice. The solution you use with the
instrumentation should not contain any particulates or water. You must not inject water into the GC. You must not inject particulates into the GC
or HPLC. It is best if the solvent you
choose for HPLC is miscible with water.
Which
technique will be most useful for your analysis?
The
HPLC detector is a UV/Vis detector with a wavelength range of 200-800 nm. Which wavelength do you think you should use
for the analysis? How could you decide?
Good
luck, have fun, and be creative!