Thin Layer Chromatography

There are various techniques to separate a mixture of compounds from each other. One of the commonly used way to isolate compounds from a mixture of two compounds is called extraction. This method of extracting two compounds from each other relies on the different solubility of the compounds in two different solvents.

Adsorption chromatography occurs when “one substance form[s] some sort of bonds to the surface of another one”, creating intermolecular forces between the two substances (Chemguide). For thin layer chromatography, the components of the mixture are adsorbed onto the stationary phase that covers the plate (Chemguide). The more polar a substance is, the more strongly adsorbed it is (Chemguide) and the strong intermolecular forces then result in a slower rate of migration with respect to the moving phase. As the solvent touches the TLC plate, the solute (mixture) is allowed to move up the TLC plate

The stationary phase will absorb or slow down different components of the tested solution to different degrees creating layers as the components of the solution are separated. Chromatography was invented by the Russian botanist, Mikhail Tsvet. Chemists use this process to identify unknown substances by separating them into the different molecules that make them up.

The purpose of this separation of a mixture lab is to give students the challenge of figuring out how to separate a provided mixture, and following through with their procedure. The mixture is composed of salt, sand, poppy seeds, and iron filings, and all of these components should be separated and dried as well as possible by the end of the lab.

Chromatography is a fairly simple process. First, you put a dot of ink(or in our case, the M&M food dye) near the bottom of some chromotography paper (also known as filter paper), and then hang the paper vertically with its lower edge (the one closest to the spot of dye) dipped in a solvent (In our case, the sodium chloride solution). Capillary action forces the solvent to travel up the paper, where it meets and dissolves the ink. The dissolved ink (which is the mobile phase) slowly travels up the paper (the stationary phase) and separates out into its different elements. Another way of describing it is to think of the liquid as an adhesive-like liquids, some of which stick more to the solid and can travel more slowly than others. This is

On a thin chromatography plate, five spots were placed ( as shown in table 2) and the plate was developed using chloroform/methanol. This was later visualized with dragendorff’s reagent under the UV light. All separated components were observed, identified and recorded.

By separating mixtures and identifying how different compounds can work together by moving within the developer. The amino acids used interact in two phases, the mobile and the stationary phase. Thin layer chromatography works mostly on capillary attractions. Due to surface tension interactions the mobile phase is forced upward to the stationary phase because of the capillary attractions. A-amino acids are the 20 common amino acids.

Care was taken to ensure that the spot got no bigger than 3mm diameter. More drops were added each time after the spot dried properly. The drops were added until the spot turned dark green which took about 5-10 drops. 10ml of running solvent was added into the chromatography tank (made up of 5 parts cyclohexane: 3 parts propanone: 2 parts petroleum ether).

It can give the polarity of that solution, reactivity of the solution, the phase of the reaction of the solution and the hydrophobicity of the solution. With this, one can determine the type of bonds in a solution relative to the other solutions as well as relative to the developer. There are three steps to the process of Thin Layer Chromatography; spotting, development (mobile phase), and visualization. During the spotting process solution(s) is/are dabbed with a capillary tube on the origin line of the TLC sheet to the required amount to give a starting point. TLC sheets have a polar silica gel on them which will react with the dabbed solution(s). The more polar the solution the more it will react with the polar silica gel. Once placed in the developer tank the mobile phase begins, as the somewhat polar developer (less polar than the silica gel) will move up the the TLC sheet through capillary action. The amino acids that are more hydrophobic will move along with the developer upward and away from the silica gel whereas the more hydrophilic amino acids will be more attracted to the polar silica and will move less than hydrophobic amino acids which are more attracted to the mobile phase caused by the developer. The solvent front is determined when the developer has almost reached to top of the TLC sheet. It is important to avoid it reaching to top, because it can cause a skew in data if allowed. The amino acids that are first to reach the top will sit at the top while the other less hydrophobic amino acids will get closer causing a skewed perspective in polarities between the amino acids at the top and the rest. After this the TLC sheet is removed, the solvent front is drawn, and the sheet now needs to dry. The next step in the development phase is helpful when identifying differences in amino acids. The TLC sheet is sprayed with ninhydrin which catabolizes the amino acids, then

In this experiment, the technique of thin layer chromatography is used to identify the identity of unknown. To aid in seeing the spots from the thin layer chromatography, UV light and iodine adsorption is used.

Through this experiment, I determined the components of a mixture of compounds by Thin-layer Chromatography (TLC). By using this method, I was able to make an identification by detecting the presence or absence of particular compounds by comparing the Rf values of known compounds to an unknown sample. For this experiment, the list of possible compounds in the samples are as follows: Acetaminophen, Aspirin, Salicylamide, Caffeine, and Phenacetin. To compare the Rf values of the possible compounds to an unknown sample, I chose TLC 4 as my unknown. Although I calculated several Rf values, the only values that were important were the values of the spots of the known compounds that lined up with the unknown spots on the TLC plate. Through careful

Chromatography is a separation technique in which the mixture to be separated is dissolved in a solvent and the resulting solution, often called the mobile phase, is then passed through or over another material, the stationary phase. The separation of the original mixture depends on how strongly each component is attracted to the stationary phase. Substances that are attracted strongly to the stationary phase will be retarded and not move alone with the mobile phase. Weakly attracted substances will move more rapidly with the mobile phase.

Introduction Chromatography is a separation technique used to obtain pure substances from mixtures based on attraction of intermolecular forces. There are two phases to the technique: the stationary and the mobile phase. The stationary phase provides support for compound migration and is immobile on a column or plate. The mobile phase is carries the compounds, which travel from a start to an end point. Amongst all of the various types of chromatography, paper, thin layer, liquid, high pressure liquid, and gas are a few examples.

The purpose of this lab was to perform thin layer chromatography test (TLC) and to calculate melting point to identify the components of a binary unknown mixture. For the purpose of the experiment, unknown #4 was chosen to test which of the following compounds were in it: ibuprofen, diphenhydramine HCl, caffeine or aspirin. The TLC test for unknown #4 resulted in two different spots that had R푓 values of .16 and .46. For the known compounds, the R푓 values were as followed: aspirin .64, ibuprofen .66, diphenhydramine HCl .5, and caffeine .28. From these results, it was concluded that the unknown consisted of diphenhydramine HCl and caffeine.

The diffusion coefficient, also called ‘diffusivity’ is a parameter that is indicative of the diffusion mobility- that is, it presents a mechanism for measurement for the diffusion speed of a solute’s vapor in a gas. The speed of chromatography is determined by the diffusion speed of the solute in the carrier gas. A molecule evaporating from the stationary phase and proceeding into the stream of gas should be capable of diffusing back into the stationary phase before having to undergo the partitioning process again. It is this diffusion of molecules that set apart the gases. In order to obtain a good separation, the most desired carrier gases are those that come in contact with the column a significant number of times. There is a limit to this however, the more time that the gas is given for radial diffusion (diffusion in the direction of the stationary phase), the more time there is for band broadening (longitudinal diffusion). For this reason there is an optimal gas velocity, where it supplies maximum contact with the stationary phase and minimum band broadening in the gas phase.