Pre Laboratory Question

1. What is Gas Chromatography (GC)?

Gas chromatography (GC), is used for separating and analyzing compounds that can be

vaporized without decomposition.

2. Explain the separation column in GC?

 the separation column is usually contained in a thermostat-controlled oven. Separating components with a wide
range of boiling points is accomplished by starting at a low oven temperature and increasing the temperature over
time to elute the high-boiling point components. Most columns contain a liquid stationary phase on a solid
support.Separation of low-molecular weight gases is accomplished with solid adsorbents.

Post Laboratory Question

1. Why we need to make sure there is no bubble in syringe during injection of sample into GC

The bubbles affect the syringe’s accuracy and precision. If bubbles are present in the sample taken thus
measurements recorded will be less accurate and less efficient

THEORY

Like for all other chromatographic methods, a mobile phase and a stationary phase are required. Gas such as (for
example) helium, flows through the column, this is called as the mobile phase or ‘carrier gas’ which serves to
carry the sample from the injector, through the column and into the detector. The column in which contains inert
solid chemically coated with a liquid, is called the stationary phase. The stationary phase selectively interacts with
the components in the sample and achieves the separation. If the component does not interact with the column, it
moves through the column. If the component interacts with the column, a longer time is needed for the sample to
travel through the column. Retention time relates much to this experiment as to its relation with the stationary
phase. Retention time is the time required for the component to appear at the detector. Components that move
through the column quickly have short retention time.
The main reason why different compounds can be separated this way is the interaction of the compound with the
stationary phase. The stronger the interaction is, the longer the compound remains attached to the stationary
phase, and the more time it takes to go through the column which means longer retention time.

Diagram drawn below shows the mobile phase (carrier gas) forwarding to the stationary phase into the column
and readings will be recorded through the detector.

DISCUSSION

An experiment on the separation of an alcohol mixture was conducted by using the gas chromatography method.
The apparatus includes the Gas Chromatography system which consists of the mobile phase, stationary phase and
a detector. The mobile phase, in other words, the ‘carrier gas’ functions to carry the sample through the stationary
phase and into the detector. As for the stationary phase, also called as the column, respectively interacts with the
components in the sample and accomplishes the separation based on the interaction in which relates to the
retention time. Settings for the Gas Chromatography were constant at column temperature of 100°C, injected
temperature of 120°C and detector temperature 130°C. In this experiment, chemicals like methanol, ethanol and
an unknown mixture of alcohols were used.

Measurements like retention time and the percentage composition were taken for each alcohol sample, methanol,
ethanol and unknown mixture of alcohols. The measurements were recorded down from the graph processed on
the computer which is attached by the detector. The retention time for methanol and ethanol obtained were
2.213minutes and 6.686 minutes respectively. Whereas for the unknown mixture of alcohols, retention time and
the peak area #1 were observed and written down for the peaks shown in the graph processed. For peak 1, the
retention time was 1.966minutes and the peak area #1 was 3972303.69μV.s. For peak 2, the retention time was
7.503minutes and the peak area #1 was 20656456.52μV.s.

After the measurements were completely recorded into the results table, percentage X was calculated. Percentage
X is the percentage composition of each alcohol in the mixture. The calculation was done by using the formula
shown below.

PERCENTAGE X = PEAK AREA OF X x 100 / Total peak area of all peaks

Calculation was made by using the above formula. The percentage composition for peak 1 (methanol) is 1.6% and
the percentage composition for peak 2 (ethanol) is 8.4%.

There are some errors that might occur during the experiment. The predicted results might not be achieved
because of the intake of the alcohol from the sample solution using the microsyringe. Trapped air bubbles might
be present in which was not visible to the naked eye thus causes abnormality in the readings obtained. Other than
that, the microsyringe might not be thoroughly cleanse for the next injection thus a pure sample could not be taken
for the Gas Chromatography system to process. This will result in a less accurate and less precise answer.
Moreover, parallax error might contribute to one of the errors.

There are a few recommendations on how to be more cautious during the experiment on getting the perfect and
answer.
Clean the syringe by rinsing it at least 6 times with the sample. Slowly draw up the plunger to obtain the sample in
the syringe. Discharge the sample into a waste container and again slowly draw up the plunger to obtain an even
accurate measurement without any trapped bubbles. As for the parallax error, the syringe has to be vertically
stable so that the parallax error can be prevented at its minimum.
MATERIALS

APPARATUS CHEMICALS

 GC system, Perkin Elmer AutoSystem XL  Methanol

Gas Chromatograph — Thermal conductivity
detector.  Ethanol
 Column — V4-in. (o.d.) x 0.5- m Pgropack
column  Unknown mixture of alcohols
 Microsyringe (10μL)

SUMMARY
This experiment is all about the separation of an alcohol mixture using gas chromatography. The parameters
involved in this experiment are retention time for methanol and ethanol, retention time for the unknown mixture
of alcohols, peak area #1 and the percentage composition. The purposes of this experiment are to identify the
component of an unknown alcohol mixture and to determine the composition of an unknown alcohol mixture. The
purposes can be obtained by Gas Chromatography through the Gas Chromatography system, Perkin Elmer
AutoSystem XL Gas Chromatograph — Thermal conductivity detector. In the Gas Chromatography system, there
are 3 stages which are the mobile phase (carrier gas), the stationary phase (column) and the detector. The mobile
phase (carrier gas) serves to carry the sample from the injector, through the column and into the detector. The
stationary phase selectively interacts with the components in the sample and achieves the separation. During the
stationary phase (column), the gas will flow through into the detector and at the same time the components in the
column will interact with the gas depending on the time it takes to interact and from that, the determination of the
retention time of each component can be identified. Doing so, the retention time for methanol and ethanol,
retention time for the unknown mixture of alcohols, peak area #1 and the percentage composition can then be
obtained. The experiment first started by drawing up 1 microliter using a microsyringe in this case started off with
methanol. It was then added into the injector port of the Gas Chromatography system. The same steps were
repeated for the ethanol and the unknown mixture of alcohols. From that, the retention time for methanol, ethanol
and unknown mixture of alcohols were obtained. Other than that, the percentage composition of each alcohol was
also recorded down. For methanol, a retention time of 2.213minutes was obtained. As for ethanol, a retention time
of 6.686minutes was obtained. In addition to that, results for the unknown mixture were completely accomplished.
For peak 1(methanol), the retention time and peak area #1 obtained was 1.966minutes and 3972303.69μV.s. For
peak 2(ethanol), the retention time and peak area #2 obtained was 7.503minutes and the peak area #2 was
20656456.52μV.s. Based on the results, the theory and objectives were achieved in this experiment. As a
conclusion, by conducting this experiment, one could benefit from what they have learned and gain more
laboratory and analytical skills and most definitely be more confident and efficient as an engineer in the future.

PROCEDURE
1. The Gas Chromatography system was turned on.
 2. A microliter syringe and a vial of methanol were obtained.
3. The microsyringe was rinsed at least 6 times before used to prevent trapped air bubbles.
4. 1 microliter of methanol was drawn using the microsyringe thoroughly.
5. The methanol was inserted carefully into the injector port of the Gas Chromatography system.
6. The peak and data was obtained and recorded down for further calculation.
7. Steps 3 – 6 were repeated for ethanol and the unknown mixture of alcohols.
8. The peaks and data for ethanol and the unknown mixture of alcohols were recorded down after the peaks
were completely generated by the Gas Chromatography system.
9. The percentage composition of each alcohol in the mixture was calculated using the formula below.

PERCENTAGE X = [Peak area of X] x 100

Total peak area of all peaks

CONCLUSION

I have learned that an unknown mixture of alcohols can be identified and separated using the gas chromatography
method. I also learned that the gas chromatography system processes from the mobile phase through the stationary
phase and into the detector which generates a standard graph which determines the composition of the unknown
alcohol mixture. The retention time was obtained through interaction with the components in the column which
was carried by the carrier gas all the way into the detector and how long it takes to accomplish the separation
based on the interaction. The percentage composition was also obtained for the unknown mixture. As for that, the
objectives of this experiment have been achieved. The stability of handling the experiment can be improve even
more by reading the manual thoroughly before starting the experiment which can prevent any unneeded errors to
occur. Moreover, adding more focus while experimenting is highly recommended as it can bring more accuracy
and precision in the results.

REFERENCES

1. [Pavia, Donald L., Gary M. Lampman, George S. Kritz, Randall G. Engel (2006). Introduction to Organic
Laboratory Techniques (4th Ed.). Thomson Brooks/Cole. pp. 797–817]
http://en.wikipedia.org/wiki/Gas_chromatography [13th February 2013]
2. [ Copyright © 2000 by Brian M. Tissue] http://www.files.chem.vt.edu/chem-ed/sep/gc/gc.html [13th
February 2013]
3. [ Anonymous,  August 10, 2006 ] http://www.chem.ucla.edu/~bacher/General/30BL/gc/theory.html [13th
February 2013]
Ihsan will do objectives, introduction, procedure, conclusion