CHM 260 LABORATORY REPORT Experiment Number: 5 Title: Gas Chromatography Chromatography (GC)
Name: Nor Syafikah binti Mohd Nasir Student no.: 2015440114 Date of Report Submission: 15th December 2017 Lab Partner’s Name: Aqilah binti Anuar
Lyana Fasihah binti Ahmad Sobri Nur Atiqah Farzana binti Zaini Lecturer’s Name: Miss Hanani binti Yazid
EXPERIMENT 5: Gas Chromatography (GC) OBJECTIVES 1. To determine the retention retention times tR of n-butanol and 2-propanol. 2 -propanol. 2. To identify the components components present present in a standard mixture based on on the tR. 3. To identify the components present in an unknown unknown sample. 4. To determine the effect of temperature on tR and Rs. INTRODUCTION Gas chromatography is an analytical separation technique that analyses compounds eluted from the column, which carried through the column by a gas mobile phase. The carrier gas in our experiment was nitrogen. We used nitrogen because it is inexpensive but gives reduces sensitivity. A detector was located at the end of the column in gas chromatography to measure the solutes that elute from it. In order to obtain an ideal chromatogram, there are many parameters that need to be adjusted. Ideal parameters give chromatograms with the high resolution in the short amounts of time. There are many parameters that can affect both the elution time and the resolution but for this experiment, we focused on effects of temperature and pressure. In gas chromatography, an increase in temperature is only favoured up to a certain point. The increase temperature reduces the time of elution for all the analytes, but after a certain point, it causes a decrease in the resolution. Pressure also needs to be controlled in order to obtain a favourable chromatogram. High pressure causes backflow which causes elution time to increase. Since the temperature and pressure are dependent on each other and it would take too long to figure out mathematically, the parameters were optimized in our experiment with the Simplex Optimization software. The Simplex Optimization software can only be used if the parameters being optimized are dependent on each other. This software used data from test runs to calculate what it thought to be a good set of parameters. The results from those parameters were then reentered into the system to make a better measurement. In our experiment, we performed as many trials as possible in the time allotted. In the end, we used the parameters that gave a chromatogram that looked to have the highest resolution in the shortest amount of time.
APPARATUS Syringe Beaker Dropper CHEMICALS 2-propanol butanol
n-
Standard mixture of 2-propanol and n-butanol (1:1 ratio) Unknown sample PROCEDURE A. Sample Handling 1. The syringe was was rinsed before it was filled with the sample. The volume volume of the sample may be more than the required volume. It was make sure that no bubbles in the syringe.
Tap the syringe gently to remove any air
bubbles. 2. The syringe was was hold vertically, needle up and the plunger was was pushed to the required volume at eye level. The excess sample was removed using a tissue. B. Operation of the GC 1. The sample was injected injected into the septa. 2. The oven column column was checked. checked. The instrument was was make sure is in the off mode. 3. The instrument was switched switched on. The warning tone will ring if the gas is not enough. 4. “Instrument 1 online” was clicked in window screen. The instrument is allowed to setup itself. 5. After setup is completed, “method” was click → “edit entire method” → “ok”. 6. The title was entered and click ok.
7. To select injection, click “manual”. To select injection location, click “back”. At instrument, edit inlet, choose “back” “back” and keep in inf ormation. ormation. 8. If the sample is in high concentration, “split” mode was chosen. If sample is in low concentration or in small quantities, “splitless” was chosen in inlet. 9. Go to column section, “column no. 2” was chosen. At inlet column, “back” was chosen. At mode mode column, “constant pressure’ was chosen and at outlet column, “ambient” was chosen. 10. Go to detector column. FID was used. 11. The parameter was injected. (time:5min, 1µL). 12. After 12. After doing all of the above, “ok” was clicked. clicked. 13. “apply” was clicked → ok → signal detail → ok → edit integration event→ ok → specify report → ok → run time checklist → ok. 14. Go to “file”, click “save”, “method”. Keep in the command. 15. During the injection, make sure that no bubbles appear in the syringe. 16. Go to “run control”, click “sample info”. The name was set in the “operator name” column. 17. Set signal 2, the sample name was filled in. 18. Click “run method” and the instrument will wait for injection. 19. The sample was injected quickly and the button “start” was pressed quickly on the instrument. Then, the syringe was quickly pulled from the septa. 20. Go to data analysis, click “file” then “load signal”. 21. “calibration” was entered, click “new calibration table”. The name was entered and the document was printed. 22. For the next sample, “data analysis” was clicked and steps 17-21 17 -21 were repeated.
QUESTIONS 1. State the type of of compounds which which are suitable for analysis using GC. The type of compounds which are suitable for analysis using GC are hydrocarbons,
halogenated
compounds,
compounds
containing
halogens, sulphur or nitrogen and organic compounds.
2. Why is FID a suitable detector detector for this analysis? analysis? FID is a suitable detector for this analysis because FID is used to detect hydrocarbons. hydrocarbons. It will not detect non-carbon containing compounds. This detector responds to all organic compounds except formic acid and the response is highest for hydrocarbons. Besides that, the detector is insensitive to H2, O2, N2, SiCl4, SO2, NO2, H2O and NH3. FID requires hydrogen supply and oxygen supply. Lastly, FID exhibits high sensitivity.
3. List two factors which which can increase increase the efficiency of a GC column. Factors which can increase the efficiency of a GC column is lengthen the column. Besides that, reducing the packing size of column can increase the efficiency of a GC column.
DISCUSSION
In the experiment, retention time plays big role in analysing the sample in gas chromatography. For the first part of the experiment, retention times are differentiated according to the number of carbon, molecular weight and the boiling point of the samples. Graphs plotted from these readings that obtained from the chromatography shown that log t r is proportionally increase when number of carbon is increased. It goes the same with molecular weight and boiling point. Log t r increase when the molecular weight and boiling point of the compound are increased. This data concluded to the relationship that w hen the number of carbon in samples tested increased, their molecular weight also increased and so with their boiling point. Therefore, the retention time, time for a maximum of symmetrical peak
to occur is also increased. Next, the temperature changed during the experiment of GC effected on tr and and Rs. The higher the temperature was set, the longer it take for the compounds to elute. Therefore, the resolution will increase resulting the increasing of the efficiency. Based on the data obtained, when the temperature was 70 C, the retention time for the compounds standard mixture is 1.557 min for 2°
propanol and 1.999 for n-butanol. For the second injection, the retention time of 2of 2propanol was 1.561 min and n-butanol was1.995min. For the unknown sample, its retention time was 1.539min, so it shows that unknown sample was 2-propanol. Then, the temperature was increased to 100 C and the standard mixture was °
injected. The graph plotted shows to peak with retention time 1.586 min and 1.725 min. Based on the retention time obtained, we can know that 1.585 min was retention time for 2-propanol while 1.725 min was retention time for n-butanol. Next, when the temperature was 140 C, the retention time for 2-propanol peak was 1.677 °
min and 1.732 min for n-butanol. During the experiment was conducted, there were several precautions to be taken in order to minimize errors in the data. Firstly, shake all the solution adequately to ensure dissolution for 5min before injection into chromatograph. Then, make sure the column is not clogged, it maybe cause by the precipitation of proteins in the column caused by removal of stabilizing agents during fractionation. Beside that, the syringe was rinse and clean before and after each sample was injected to prevent any contaminant and other solution that will affect the process. Lastly, avoid formation of bubbles during the experiment because it will affect the reading in the column while the measurement was taken.
CONCLUSION At the end of the experiment, we can determine the retention t ime of n-butanol and 2-propanol which are 1.999 min and 1.557 min respectively. Beside that, we managed to identify the components present in a standard mixture based on the t r.Then, the components present in the unknown sample was identified. The component present can be known based on the retention time obtained in the graph. It shows that 2-propanol was present as its retention time was 1.539 min. Last but not least, we had learned the effect of temperature on t r and and Rs. As the temperature increase, the retention time, tr will will increase. So the Rs will increase as well.
REFRENCES 1. Ariffin Z., 2016, Basic Instrumental Analysis Analysis Laboratory Experiments Experiments for An Introductory
Course
in
Instrumental
Analysis,
Gas
Chromatography
Experiment 5. 2. https://www.scribd.com/doc/38677786/Experiment-of-Gas-Chromatography https://www.scribd.com/doc/38677786/Experiment-of-Gas-Chromatography,, retrived on 9 December 2017, 5.08pm.
