GC-MS/GC-FID Lab Report
Introduction: Gas Chromatography is the separation technique that is used for organic solvents
or volatile organics. It allows for the basic separation of compounds and their identification by
analyzing the retention time or the time it takes the sample to stay in the column and then leave
to go to the detector. Since the compounds that are used are volatile organics, there’s the
possibility that they will vaporize without decomposing. There are multiple detectors that can be
used for the analysis of organic compounds when using the GC. The two that were used in this
lab were mass spectroscopy (MS) and flame ionization detector (FID). These detectors can be
used to test the purity of a substance or be able to separate the components of a mixture. The GCMS can specifically be used to identify different substances in a sample and is most commonly
used for drug detection, fire investigation, and environmental analysis. The GC-FID on the other
hand is primarily used for the detection of organic compounds like proteins, nucleotides and
pharmaceutical products. It is also good with detecting hydrocarbons and other flammable
products but destroys most of the components in the process.
Purpose: The purpose of this lab was to get familiar with the GC-MS and GC-FID by running
various hydrocarbons and determining their retention times and resolution as well as figuring out
what compounds are in mixtures and unknown compounds.
Methods: Day 1: We worked on the GC-MS the first day of lab. We ran various hydrocarbons to
determine their retention times and resolution through the mass spec. We made sure the helium
was turned on and the pressure was good and once the software and instrument were ready we
did the samples. First we did hexane as a warm up or starter of the instrument and no data was
obtained from this run. The samples we ran where we obtained a chromatogram included octane,
undecane, nonane, dodecane, and an unknown sample. Each run took 9 minutes to ensure that all
potential peaks would appear on the graph.
Day 2: During this lab period we worked on the GC-FID and used the same hydrocarbons
that were used for the GC-MS. First we made sure all the gases were turned on including helium,
hydrogen, and compressed air and waited for the flame to turn on. Once the computer and
instrument were ready we ran our samples. We ran mixtures of octane/dodecane, and
octane/nonane/dodecane, individual samples of octane, nonane, and dodecane, and an unknown.
Each scan took 10 minutes to ensure that all potential peaks would appear on the graph. A scan
of each of these runs were obtained and analyzed for retention time and determination of the
unknown sample.
Results: All chromatograms and mass specs are located in the lab notebook. Analysis of the
chromatograms was very simple. We just had to measure the single peak on the scan and find the
time where that peak is and then compare our results to the known retention times of those
hydrocarbons. For the GC-MS results we got a retention time for each of the samples that were
run:
Octane: 2.5 min; Undecane- 4.1 min; Nonane- 2.85 min; Dodecane- 4.55 min and the
unknown had three peaks meaning that the sample contained 3 hydrocarbons each with times of
2.3 min, 2.8 min, and 4.55 min which shows that the unknown contained a mixture of octane,
nonane, and dodecane.
For the GC-FID results we obtained a chromatogram of each run with an area and
retention time of each peak:
Octane- .897 min; Dodecane- 3.101 min; Nonane- 1.329 min; the mixtures had multiple
peaks to represent the different compounds in the mixture:
Octane/Dodecane- 3.012 min and .845 min; Octane/Dodecane/Nonane- 3.012 min, 1.280
min, and .843 min. The unknown also contained three hydrocarbons with retentions times of .817
min, 1.217 min, and 2.937 min. These retention times show that the unknown contained octane,
dodecane, and nonane.
Conclusion: The experiments were overall successful. Data was obtained from every sample
that was run through the instruments and analyzed for content. However we were not able to
obtain the mass spec print-outs because of printing issues and the computer telling us there was
an error. After trying multiple solutions we were still unable to obtain the print-outs but we were
able to get one for dodecane and that can be found in the lab notebook. The mixture retention
times and peaks were consistent with the individual scans and showed that the instrument is
working and backs up what hydrocarbons we put in the mixture. Also the unknown was
successful and we were able to determine its components based on its retention times and peaks
and comparing them to the individual scans to see what was in the unknown. There were no
major problems with the lab or anything trouble shooting. As long as the gases are turned on in
the gas room and on the lab bench and waiting for the instruments to be ready to run samples,
everything should run smoothly. The only problem we ran into was not waiting long enough for
the GC-FID to say be ready and for the flame to come on, but that was due to not turning the
nozzles on the gases in the gas room. Once we figured out what the problem was, we resolved it
and continued on with the sample runs and had no other problems.