Lab 6:
Gas Chromatography Flame Ionization Detector
INTRODUCTION
The gas chromatography instrument is a very useful instrument for organic chemistry. The GC is
chromatography instrument that is meant for separation of volatile organic compounds. When using the
GC for separation, it imperative that one analyze that sample before running it through a GC. In order
for a sample to be run on a GC it must be volatile, in that sense, it must have a very low boiling point,
preferably able to evaporate at room temperature stemming a little bit above and below that criteria.
When samples are ran on the GC that information is relayed to the researcher via a chromatograph.
Using a chromatograph one can obtain a wide range of information. Also, one can calculated
concentration and retention times. The GC has two characteristic detectors, (1) is the mass spec
analyzer, and (2) a flame ionization detector. Both detectors are unique. The FID analyzer detector was
the detector used in this experiment.
PROCEDURE
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Made sure the helium, compressed air and hydrogen tanks are on and reading 80psi.
Then made sure the desktop knobs were turned on, and ready to go. Also, made sure
the flame on the GC was lit.
Using the computer, turned on the GC software, and made sure the GC-FID software
was activated.
Checked the instruments parameters, and made sure all parameters were set to the
right setting and the appropriate method was selected.
Sample Preparation
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The syringes were cleaned with acetone before and after each use.
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Five organic solvents were obtained and labeled.
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0.1mL (10uL) of standard sample with 10uL of hexane (solvent).
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Using the syringe, took up 1uL sample, and 1uL of air.
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Sample was ready for injection.
GC Analysis Procedure
minutes.
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When syringe was ready, injected the sample in the GC-FID and ran the sample for ten
After all standard were ran, ran an unknown mixture.
Special Notes
The chromatograph of the standard should all have two peaks, (1) for hexane, and (2)
another peak for the analyte, which is whatever we dissolved in the sample.
RESULTS
RETENTION TIMES OF SAMPLE STANDARDS & UNKNOWNS (cm)
PEAK 1
PEAK 2
PEAK 3
PEAK 4
PEAK 5
Unknown
1.20 cm
1.90 cm
2.75 cm
6. 70 cm
---
Undecane
1.20 cm
5.40 cm
6.75 cm
---------
Nonane
1.25 cm
2.9 cm
-------------
N-Dodecane
1.30 cm
6.65 cm
----------------
Decane
1.25 cm
4.30 cm
----------------
Octane
1.25 cm
2.00 cm
---------------
The data obtained from the chromatograph using the FID, showed the retentions times
displayed in the table above. The unknown mixture had 4 characteristic peaks that showed to have the
components of 1.25 cm (hexane solvent peak), 1.90 cm (Octane), 2.75 cm (Nonane), and 6.70 cm (Ndodecane). The data showed to be a little more accurate each spectra obtain for each standard had
mostly two peaks which corresponded to the solvent peak and the sample standard. The only sample
that showed to have contamination was Undecane because three peaks were obtained. The peaks
showed to be consistent with 1.20 -1.25cm being the solvent peak. Overall, results seemed to be way
better than the GC-MS.
CONCLUSION
The unknown sample contained Octane, hexane, nonane, and N-dodecane. I feel more
confident with this decision because when using the GC-MS the spectrum obtained seemed messed up
and gave funky results. However, using the GC-FID seemed to produce better results. The spectra
weren’t skewed in any way, although some standard did show some type of contamination it seemed
minor. All the data showed to have a solvent peak of about 1.20 -1.25 cm and one other peak that was
characteristic for that particular sample standard. I was able to look at the data and easy pick out which
sample were present in the unknown because the retention times were very similar.
When related the GC-MS and GC-FID I think for this experiment the GC-FID showed better
results because separation was very good and the resolution between to peaks were good as well. The
GC-MS spectrum showed peaks that were much skewed. The peaks didn’t separate well. I think that in
reality both instruments are good at separating volatile organic solvents. However, I think the GC-MS
might have had something wrong with it and that could have been a reason why it was not working
properly.