Lab 6 Gas Chromatography and Thin Layer Chromatography

Lab #6: Gas Chromatography and Thin Layer Chromatography

Background

Chromatography is used to separate, analyze, and identify mixtures or compounds of substances into their components (15). Every type of chromatography has a mobile phase and a stationary phase. The mobile phase is a liquid or gas that carries the sample and the stationary phase is an adsorbent or liquid that the sample is carried through (15). For thin layer chromatography, an individual uses a thin, uniform layer of silica gel and is packed into a column. The silica is the stationary phase and the mobile phase are the liquid solvents hexane and ethyl acetate. Depending on the intermolecular interactions with either the stationary or mobile phase, the compounds in thin layer chromatography will travel at different rates (16). Also, this difference in attraction is what allows the substances to be separated from each other (16). The stationary phase also often contains a substance that is shown under UV light, which will be shown in this experiment (15).

Gas chromatography is often used in many research and industrial laboratories for identification and quantitation of compounds in a mixture (17). Just like thin layer chromatography, gas chromatography involves a mobile and stationary phase, and separation of compounds is based on the different strength of attraction of the compounds with the stationary phase (17). The stronger the attraction to the stationary phase, the longer it takes for the compound to exit through the column, which means a longer retention time (17). Factors such as vapor pressure polarity of components and stationary phase, column temperature, carrier gas flow rate, column length, and amount of material injected are all things that influence the separation of the components (17). Different detectors as well can be used for gas chromatography, some being mass spectrometer, flame ionization detector, thermal conductivity detector, and electron capture detector (17).

Aim

To analyze and separate mixtures using gas chromatography and thin layer chromatography. Specifically, our aim for this experiment was to assess the purity of ferrocene and acetylferrocene samples that were separated previously via absorption chromatography, by using thin layer chromatography.

Physical Properties and Hazards

Name of Chemical	Chemical Formula	Melting Point	Boiling Point	Solubility in water	Density
Ferrocene	C10H10Fe	172.5°C (or 342.5°F)	249°C (or 480.2°F)	Insoluble	1.11g/cm3
(1)
Acetylferrocene (2)	[Fe(C5H4 COCH3) (C5H50)]	81°C - 83°C (or 178°F181°F)	161°C (or 321.8°F)	Insoluble	1.014g/mL
Hexane (3)	C6H14	-96°C – -94°C (or 141°F – -137°F)	68°C (or 154.4°F)	9.5mgL-1	655kg/m3
Acetone (4)	C3H6O	-95°C (or -139°F)	56°C (or 132.8°F)	Miscible	791kg/m3
Ethyl Acetate (5)	C4H8O2	-83.6°C (or - 118.5°F)	77.1°C (or 170.8°F)	8.3g/100mL (at 20°C)	897kg/m3
2,4,4-trimethyl- 1-pentene (6)	C6H16	-101°C (or - 149.8°F)	101°C103°C (or 213.8°F217.4°F)	Immiscible	0.708g/mL at 25°C
2,4,4-trimethyl- 2-pentene (7)	C5H10	-165°C (or - 265.4°F)	30°C (or 86°F)	Immiscible	640kg/m3

Hazards

Name of Chemical	Chemical Formula	Hazards
Ferrocene	C10H10Fe	-combustible (8). -inhalation can cause sore throat (8). -exposure to skin can cause redness (8). -exposure to eyes can cause redness and pain (8).

Acetylferrocene	[Fe(C5H4 COCH3) (C5H50)]	-may be fatal is swallowed; poison by ingestion (9). -toxic is absorbed through the skin (9). -may cause eye, skin, and respiratory tract irritation (9). -may cause digestive tract irritation (9).
Hexane	C6H14	-highly flammable (10). -vapor/air mixtures are explosive (10). -inhalation may cause dizziness, drowsiness, dullness, headache, nausea, weakness, unconsciousness (10). -contact with eyes can cause redness and pain (10). -ingestion can cause abdominal pain (10).
Acetone	C3H6O	-highly flammable (11). -vapor/air mixtures are explosive (11). -inhalation can cause sore throat, cough, confusion, headache, dizziness, drowsiness, and unconsciousness (11). -contact with skin causes dry skin (11). -exposure to eyes can cause redness, pain, blurred vision; possible corneal damage (11). -ingestion can cause nausea and vomiting (11).
Ethyl Acetate	C4H8O2	-highly flammable (12). -vapor/air mixtures are explosive (12). -inhalation can cause cough, dizziness, drowsiness, headache, nausea, sore throat, unconsciousness, and weakness (12). -can cause dry skin (12). -contact with eyes can cause redness and pain (12).
2,4,4-trimethyl- 1-pentene	C6H16	-highly flammable; heating will cause rise in pressure with risk of bursting (13). -vapor/air mixtures are explosive (13). -inhalation will cause confusion, cough, dizziness, drowsiness, dullness, headache, and sore throat (13). -contact with skin will cause redness (13).
-contact with eyes will cause redness and pain (13).
2,4,4-trimethyl- 2-pentene	C8H16	-highly flammable (14). -vapor/air mixtures are explosive (14). -inhalation will cause drowsiness, headache, and nausea (14). -contact with skin will cause redness (14). -ingestion will cause abdominal pain and vomiting (14).

Introduction

Thin layer chromatography is a solid-liquid technique where the solid phase is the stationary phase and the liquid phase is the mobile phase (18). The stronger a certain compound is in the mixture is adsorbed into the stationary phase and it will take less time to exit the column (18). Some common uses of thin layer chromatography are to determine the number of components in a mixture, to determine the identity of two substances, to monitor the process of a reaction, to determine the effectiveness of a purification, to determine the appropriate conditions for a column chromatographic separation, and to monitor the column chromatography.

Gas chromatography is the separation of compounds based on the different attractions of the compounds with the stationary phase. The important components of gas chromatography are the carrier gas, the sample injection port, the columns, the column temperature, the detectors (19). The carrier gas must be chemically inert, which include gases such as helium, nitrogen, and/or argon (19). The sample injection port should not be too large, and when injecting a sample into the port, it should not be injected too slowly (19). There are two general types of columns: packed and capillary (19). Capillary columns have an internal diameter of a few tenths of a millimeter, whereas packed columns contain a divided, inert, and solid support material coated with the liquid stationary phase (19). The column temperature must be controlled within a few tenths of a degree to ensure precise results (19). Lastly, there are many different detectors an individual can choose from that give several types of selectivity (19). Depending on what an individual is trying to accomplish in an experiment, different types of detectors offer different results that are more accurate and suitable.

Procedure

Thin Layer Chromatography

1. We first filled a glass chamber with a 3:2 solvent of hexane to ethyl acetate to a few millimeters in a beaker.
2. We then drew two lines on a silica plate, approximately 1cm from the top and 1cm from the bottom, and on the bottom line, we drew three dots.
3. We took our vials of ferrocene and acetylferrocene and added a few drops of acetone in both to make the compound into a liquid.
4. We then took capillary tubes and put one drop of ferrocene, one drop of acetylferrocene, and one drop of a 50:50 mixture of ferrocene and acetylferrocene on the bottom line of the silica plate. Each drop went on one of the dots we drew.
5. Next, using our tongs, we placed the silica plate into our beaker with our 3:2 hexane to ethyl acetate solvent and covered the top of the beaker.
6. We then watched the solvent level rise from the bottom line to the top line.
7. Each component – ferrocene, acetylferrocene, and the 50:50 mixture of both- travelled at different distances and rates on the silica plate.
8. Once each component traveled to the top line, we removed our silica plate from the beaker and placed it into the UV light to observe our results.

Gas Chromatography

1. First, we took a microsyringe and measured 1 micrometer of a compound containing 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene from vial GC#2.
2. We then slowly injected this compound into the GC machine, and simultaneously hit the “Start” button.
3. We immediately removed the syringe from the machine.
4. Next, waited a few minutes until we saw a reading appear on the computer screen.
5. Lastly, we printed out our results.

Results

1. Thin Layer Chromatography

Distance Traveled by Solvent Line	4.1cm
Distance Traveled by Ferrocene	3.2cm
Distance Traveled by Mixture	2.9cm
Distance Traveled by Acetylferrocene	2.9cm

Conclusion

For the thin layer chromatography experiment, there were noticeable differences in our Rf values for ferrocene and acetylferrocene. These differences in values can be explained by ferrocene’s and acetylferrocene’s different behaviors toward the hexane and ethyl acetate solvent. Also, in this part of the experiment, there were significant errors caused by the solvent mixture that we used. Our solvent was too polar, which caused our compounds to go all the way up to our top line. If we used a less polar solvent, like 10% ethyl acetate and 90% hexane, these errors would not have been observed. Since every lab group had these errors, it was concluded that the acetylferrocene was not pure. Although we observed this error, we were still able to successfully separate ferrocene and acetylferrocene. Also, we observed a greater Rf value for ferrocene than acetylferrocene, which makes sense because of their differences in polarity. Since ferrocene is less polar than acetylferrocene, ferrocene interacts more with the mobile phase, which is why it traveled a greater distance than the acetylferrocene.

In the gas chromatography section of the experiment, although we calculated an approximate ratio for each peak, the GC machine provided us with a more accurate reading. Our ratios we calculated came out to be 60.9% and 39.1%, whereas the GC machine gave readings of 60.4% and 33.7%. The GC machine allowed for us to get precise results, which makes this section of the lab experiment so beneficial. Using the GC machine prevented human error, and allowed for precise and accurate results.

In conclusion, gas chromatography and thin layer chromatography have both advantages and disadvantages. Gas chromatography is much more accurate in detecting different compounds and their compositions. But, compared to thin layer chromatography, gas chromatography is more expensive. Thin layer chromatography can only be used to separate volatile chemicals and does not require a machine and is inexpensive. Thin layer chromatography is more useful for separating compounds and assessing their impurities.

References

Wikipedia. (2017, June 20). Ferrocene. Retrieved from:

https://en.wikipedia.org/wiki/Ferrocene (1)

Wikipedia. (2017, June 2). Acetylferrocene. Retrieved from:

https://en.wikipedia.org/wiki/Acetylferrocene (2)

Wikipedia. (2017, June 22). Hexane. Retrieved from:

https://en.wikipedia.org/wiki/Hexane (3)

Wikipedia. (2017, June 25). Acetone. Retrieved from:

https://en.wikipedia.org/wiki/Acetone (4)

Wikipedia. (2017, June 7). Ethyl Acetate. Retrieved from:

https://en.wikipedia.org/wiki/Ethyl_acetate (5)

Book, Chemical. 2,4,4-trimethyl-1-pentene. Retrieved from:

http://www.chemicalbook.com/ChemicalProductProperty_EN_CB8397241.htm (6)

Wikipedia. (2017, January 17). Pentene. Retrieved from:

https://en.wikipedia.org/wiki/Pentene (7)

Centers for Disease Control and Prevention. (2014, July 1). Ferrocene. Retrieved from:

Sheet, Material Safety Data. (2008, January 24). Acetylferrocene. Retrieved from:

https://fscimage.fishersci.com/msds/69220.htm (9)

Centers for Disease Control and Prevention. (2014, July 1). Hexane. Retrieved from:

Centers for Disease and Control Prevention. (2014 July 1). Acetone. Retrieved from:

Centers for Disease and Control Prevention. (2014 July 1). Ethyl Acetate. Retrieved from:

Centers for Disease and Control Prevention. (2014 July 1). 2,4,4-trimethyl-1-pentene. Retrieved from:

Centers for Disease and Control Prevention. (2014 July 1). 2,4,4-trimethyl-2-pentene. Retrieved from:

Chemguide. Thin Layer Chromatography.

Thin Layer Chromatography. Retrieved from:

http://www.users.miamioh.edu/gungbw/CHM254_html/pdfs/TLC_Student.pdf (16)

UCLA. (2016, April 1). Gas Chromatography. Retrieved from:

http://www.chem.ucla.edu/~bacher/General/30BL/gc/theory.html (17)

Home, Online Lab Manual. Thin Layer Chromatography, Retirved from:

http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/Tec hniques/TLC/thin_layer_chrom.html (18)

University, Sheffield Hallam. Gas Chromatography. Retrieved from:

https://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/gaschrm.htm (19)