Experiment 14 - Gas Chromatography and Carvone Analysis
Pre-Lab:
Theory of gas chromatography, theory of odor detection and chiral recognition - 5 pts
Structures of carvones and limonene - 3
MSDS of carvones and limonene - 3
Data Tables: only all the data you will record in the lab during the expt. - 4
Lab Report:
1. Record the following parameters for this gas chromatography separation. 3 pts
a. Oil that was injected and its odor.
b. Volume injected
c. Type and length of column used.
d. Column temperature
e. Detector temperature
f. Injection port temperature
g. Carrier gas identity
h. Flow rate of carrier gas in ml/minute
i. Chart speed in cm/minute
j. Attenuation
k. Polarity
2. Gas chromatogram with the peaks identified on the chromatogram. 2 pts
3. Retention time for both peaks in minutes. Show lines on chromatogram that were measured. 2 pts
4. % composition for both peaks (triangulation method.) Show all measurements on the chromatogram
and all calculations. 4 pts
5. Refractive index for both carvones - record temperature and show calculations for temp.
corrections. 4 pts
6. Optical rotation for both carvone enantiomers:
a. Turn on the polarimeter and let it warm up for 5 minutes.
b. Calibrate the polarimeter with no sample tube in the polarimeter by finding the zero
degree point (it is not exactly on zero.) Set the scale exactly on zero and note that one
hemisphere is dark and the other one bright. Turn the scale to the left and/or to the right
of zero, no more than 10 degrees, until you notice that both hemispheres have equal
brightness. If you continue turning the scale past this point you will notice that the other
hemisphere is now dark. Go back to where the two are both equally bright and take a
reading. Record this value and note whether it was to the left or right of the actual zero.
c. All scale readings must be corrected. Either add or subtract your new zero reading from every polarimeter reading that you record to reflect the actual number ofdegrees through which you turned the movable scale.
d. Taking a scale reading: Read the angle off of the fixed, circular scale where the zero on
the (movable scale) intersects the circular scale. The final digit (one after the decimal) is read from the vernier divisions to the right of the zero if you originally rotated
the entire scale to the right, and from the vernier divisions to the left of the zero if your
original rotation was to the left. Remember, to take a vernier reading, record the line
on the vernier scale (0-9) that lines up exactly opposite a line on the fixed, circular scale.
Readings to the left of zero will be negative; readings to the right of zero are positive. The
correct sign must always be used
e. Insert the sample tube into the polarimeter with the wider end up.
f. Finding the correct angle of rotation: it will be necessary to do this in a darkened room
in order to see the circular field which will be much dimmer than it was when there was
no sample tube in the polarimeter. Turn the vernier slowly until both parts of the field have
exactly the same coloring (equally dim). It will be easier to find the right adjustment if the
vernier is turned a little bit too far to the right so that one hemisphere is dark and then a
little too far to the left so that the other hemisphere suddenly darkens. The correct
adjustment is somewhere in the middle when both hemispheres have the same intensity.
g. For the (-) carvone: Take 2 readings on the polarimeter, one turning to the left (this
reading will be less than 90 degrees and will be negative) and the other turning to the right
( this reading will be between 90 and 180 degrees and will be positive). Subtract 180
rom the reading to the right. Give the raw data and show your calculations. 2 pts
For the (+) carvone: Take 2 readings, one to the right (this reading will be less than
egrees and will be positive) and the other to the left (between 90 and 180 degrees and
egative.) Subtract the reading to the left from 180. Give raw data and show calculations. 2 pts
h.Average your 2 readings for each carvone. Calculate the "specific rotation" for both
carvones by the formula in the text, using the density (given in the book) of the carvone for “c” in the formula and 1 dm as the length of the polarimeter tube. 3 pts
7. Weight of carvone sample collected from the GC, including weight of empty vial and weight of
vial and sample. 1 pt
8. Volume of the carvone sample (in ml) calculated from the weight and the density.
Show calculation. 2 pts
9. Calculate vol of carvone in the 50 microliters injected from the % composition of carvone from your chromatogram. Calculate % carvone recovered by volume using this value as the theoretical value.
Show calculation. 4 pts
10. Organize all of the data into a neat, easy-to-read table at the end of the lab report. Include the -/+
true values for refractive index and optical rotation. 4 pts
11. Answer the questions. 10 pts
12. Comment on your results in the conclusion, giving your values and true values when applicable.
3 pts
Total Points: 61