Chromatography is one of the most important separation techniques used in all fields of chemistry ranging from analytical chemists to pharmacists. The understanding of how chromatography works and how to operate instruments used to carry out the procedures is an important lab technique to learn.
Experiment:
Thin Layer Chromatography. Lab #10-1
Paper Chromatography. Lab #10-2
Theory:
Ethyl Acetate-Solvent used in TLC (mobile phase).
Dichloromethane- Solvent used to dissolve all samples used to compare unknown in TLC Silica Gel Plates- TLC plates. Stationary phase
Elemental Iodine- used to accentuate the spots on the TLC plates so we can measure Rf. Asprin(Acetylsalicylic acid)- First compound used on TLC plate to compare the unknown. Salicylamide(o-hydroxybenzamide)-Second compound used on TLC plate to compare unknown. Caffine(1,3,7-Trimethylxanthine)-Third compound used on TLC plates to compare unknown. Acetone- Solvent A used in paper chromatography.
Ethanol- Solvent B used in paper chromatography.
Dithiooxazmide- Spray used to show to spots on paper chromatography Sodium Diethyldithiocarbamate- Second spray used to show spots on paper chromatography Ammonia- Fumes were used to bring about the spots on the filter paper in paper chromatography.
The Essay on Advantages Of Thin Layer Chromatography (TLC)
TLC is very simple to use and inexpensive. Undergraduates can be taught this technique and apply its similar principles to other chromatographic techniques. There are little materials needed for TLC (chamber, watch glass, capillary, plate, solvent, pencil, and UV-light). Therefore, once the best solvent is found, it can be applied to other techniques such as High performance liquid chromatography. ...
Results:
Unknown in TLC was Aspirin
Unknown in Paper was Nickel
Rf Asprin-5.5cm/7= .78
Rf Salicylamide-6.3cm/7= .9
Rf Caffine-1.2cm/6.3= .19
Rf Unknown(TLC)-5.5cm/7=.78
Rf Cobalt solvent #1-5.1/6.5=.78
Rf Copper solvent #1-5.7/6.5=.87
Rf Iron solvent #1=1
Rf Nickel solvent #1-1.4/6.7=.21
Rf Unknown(Paper) solvent #1-1.3/6.5=.21
Rf Cobalt solvent #2=.88
Rf Copper solvent #2=.86
Rf Iron solvent #2=.91
Rf Nickel solvent #2=.94
Rf Unknown(Paper) solvent #2=.91
Calculations:
Rf Unknown(Paper) solvent #1-1.3/6.5=.2
Discussion:
In this Lab, I had to run some trials multiple times due to spots not showing up. The only one I am still not sure of if I got a definite mark is of Iron in solvent #1 on the paper chromatography. However, I do not think this affects my data because my unknown looks very similar to another metal. One error that was made relatively consistently was not letting the solvent rise high enough. Although this is a proportional error, I did not have time to let them continue to rise. The only trial that this caused a problem in was in the paper chromatography trial with solvent # 2. This was the last trial that I ran and was out of time. I had to pull it out before it was close to the top. The compounds however ended all at the very top unfinished so I had to extrapolate where I believed they would end if I let the solvent rise more. I believe this is still not a problem however due to the fact that my unknown solutions color, shape, and size were all consistent in both solutions, Therefore I do not have to be so consistent with the retention factor in order to know what my unknown was. If there were other metals whose color shape and Rf was closer to the unknown, this would have caused a much grater problem.
