Gas Chromatography Lab

Objective:

The purpose of this experiment is to learn how to use fractional distillation to separate a mix of isopropyl acetate and toluene, redistill them, and use gas chromatography to examine the separation.

Techniques:

Chemical Name Molecular Weight Appearance Density Amount Boiling Point

Isopropyl Acetate 102.1 g/mol Colorless liquid .88 g/mL 1.5 mL 89°C

Toluene 92.15 g/mol Colorless liquid .87 g/mL 1.5mL 111°C

• Distillation

• Gas Chromatography

Physical Data Table:

Procedures:

The following procedures were performed using pages 27-29 in Dr. Morvant and Dr. Halterman’s Organic Chemistry Laboratory Manual. 1.5mL of Isopropyl acetate and 1.5mL of Toluene were added to a 5mL conical vial by a calibrated Pasteur pipette, and then the spin

vane was added. The Hickman still and heating block was put together and aluminum foil was wrapped around the connecter and Hickman still. When the temperature increased, the thermometer was added to the Hickman still. As the temperature of the hotplate slowly increased to 80°-90°C, the solution was stirred slowly. The connector was tightened during the heating. Distillate was removed using a bent pipette, and it was placed into a .5-dram vial. Distillate was collected and put in the vial until there was 1.2mL in the vial, and then the heat was raised to 105-115°C. .6mL of the distillate was collected into another vial labeled “Fraction 2.” The remaining 1.2mL of liquid in the distillation conical vial was cooled and transferred to a vial labeled “Fraction 3.” Gas chromatography was used to analyze the three samples. A USB cable was used to turn on the mini GC and the LabQuest device. A new file was made, and the collect button brought up the “Temperature-Pressure Profile”. The parameters were modified for the isopropyl acetate and toluene samples. A syringe was 1/3 filled with Fraction one and expelled into a paper towel twice. After clearing out the syringe, it was filled with .2 µl of Fraction 1. Fraction 1 was inserted in the injection port when the GC read “Inject and select Collect simultaneously.” Before removing the needle, the collect button was pushed while depressing the syringe plunger. The data was saved, and the peak areas were calculated using analyzes, advanced, peak integration, and then signal. The starting point of the first peak was tapped on and then “add” was chosen. Then the second peak was added, and peak integration was completed. The steps involving the GC and LabQuest were repeated for Fractions 2 and 3. After that, Fraction 2 was disposed of in liquid waste. Fraction 1 and 3 were combined with another groups 1 and 3 for redistillation. The previous set up for the Hickman still was used with either Fraction 1 or 3. The heating block temperature was raised to 80-90°C for Fractions 1 and 105-115°C for Fractions 3. 1 mL of distillate was collected from either Fraction, and then GC analysis were run again and shared.
Observations:
1.5mL of toluene and isopropyl acetate each were added to a 5mL conical vial with a spin vane.

Aluminum foil was not used during the experiment to wrap around the Hickman still. The temperature of the hot plate continuously increased because the thermometer temperature increased very slowly. The stillhead started to collect condensate around 50°C which is much lower than the 80-90°C that the thermometer was supposed to read. A bent pipette was used to collect around 1.5mL of distillate that was put into a .5-dram vial. This vial was named “Fraction 1.” The hot plate temperature was increased a little more to increase the thermometer temperature in the Hickman still. .6mL of distillate was collected, using the same bent pipette, and put into another .5-dram vial named “Fraction 2.” The hot plate was turned off, and everything was left to cool for a little bit. After it cooled, around 1.2 mL of clear liquid was left in the original vial and transferred to another vial named “Fraction 3.” The syringe for gas chromatography was flushed with acetone and then with Fraction 1 before any reading was done. Because the syringe only collects .2µL of Fraction 1, the liquid wasn’t visible to the naked eye. The needle had to be twisted and rotated gently to insert into the injection port. When the LabQuest collected to data, there was one tall peak and a few little ones. The Percent Area for peak 1 was -197.78 and peak 2 was 297.78, and the Retention time for peak 1 was .700

minutes, while peak 2 was .945 minutes. The same steps were repeated with Fraction 3. The analysis had one prominent peak. The Retention time was 1.180 minutes, and the Percent Area was 100.00. Due to time restraints, redistillation was not performed.
Results:
The Gas Chromatography analysis for Fraction 1 was -197.78 and 297.78 Percent Area and .700 minutes and .945 minutes Retention Time. The Gas Chromatography analysis for Fraction 3 was 1.180 minutes for Retention time and 100.00% Area.
Discussion:
The purpose of this experiment was to learn how to perform fractional distillation, and understand gas chromatography and LabQuest used with it.

Distillation is used to separate liquids with different boiling points. Because toluene and isopropyl acetate have different vapor and composition phases, fractional distillation was used. Isopropyl acetate’s boiling point is lower than toluene’s boiling point (89°C and 111°C), meaning that Fraction 1 was isopropyl acetate while Fraction 2 was a mixture of the two, and 3 was pure toluene. Gas chromatography was only performed on Fraction 1 and 3, and a packed column was used. Isopropyl acetate and toluene’s polarity were important because the more polar the molecule, the longer it takes to come off of the column in the GC. The number of peaks showing on the gas chromatography analysis shows how many compounds are in the sample. For example Fraction 1 had two peaks, meaning there were two compounds in the sample, while Fraction 3 only had one peak. The longer the retention time, the more polar the compound was. Fraction 3 had the longest retention time, meaning it was more polar than Fraction 1. Fraction 3 was toluene, which is a more polar compound than isopropyl acetate in Fraction 1. Gas chromatography also identifies the concentration of the compound or the size of the peaks. A tall and wide peak means that there was a lot of a compound passing over the detector in the gas

chromatography.
Two peaks were seen in Fraction 1 meaning that there were two compounds in the sample. Fraction 1 should have been isopropyl acetate but some toluene could have evaporated with it. Because the thermometer wasn’t heating up very fast, the hot plate could have been heated too fast resulting in some toluene to evaporate with the isopropyl acetate and be collected for Fraction 1. Another possible source of error was from the estimation of 1.2mL in Fraction 1 and .6mL in Fraction 2. It was difficult to estimate how much was actually collected for each, Fractions 1 and 3 had around the same amount.

Conclusion:
In this experiment distillate was collected into 3 fractions depending on boiling points. 1.2mL of distillate was collected for Fraction 1, .6mL for Fraction 2, and 1.2mL for Fraction 3. Gas chromatography resulted in .700 and .945 minutes for retention time and -197.78 and 297.78 % area for Fraction 1, and 1.180 minutes for retention time and 100.00 % area for Fraction 3. Because Fraction 3 had a longer retention time, meaning it was a more polar compound, and it was collected at a higher temperature, it confirms that toluene was in Fraction 3 and isopropyl was in Fraction 1.

Morvant, M and Ronald Halterman. Organic Chemistry Laboratory Manual, 2nd ed.; The University of Oklahoma’s Center for Teaching Excellence: Norman, 2013.