Lab Report: Thin Layer Chromatography

Abstract:

The following experiment was done Wednesday June 10th and was set up in place to understand the effects of Thin Layer Chromatography, using a Sharpie marker, Acetate, and various concentration mixtures of solvents. Not only was a TLC plate apparatus set up and used to purify and separate the non-volatile substance, but also a UV light was used to measure the distance traveled by purified substances and their resulting Retention factors. Over three TLC plates with three dots each displaying various concentrations, our results indicated multiple purified colored substances separated and corresponding retention factor values, which as well determine the substances polarity.

Introduction:

        The importance of a Thin Layer Chromatography is for the separation of non-volatile mixtures and the findings of the retention factors obtained by an experiments results. This experiment itself is based on the non-covalent interactions between the stationary phase, the different compounds and the eluent/solvent. Thin Layer Chromatography is a mechanism used in order to monitor the progress of a chemical reaction and the purity of a compounds in order to identify those in a mixture. Each dot on the plate is a different component of the original mixture at the base of the plate. The TLC plate is composed of silica which itself is polar. In regards to “like dissolves like”, the silica plate will hold on strongly to those compounds which are also polar, making the compound travel a short distance then those compounds which are non-polar, do not hold as strongly, and travel farther up the silica plate. Simply the dots towards the base have a stronger interaction, while those dots which are farther up have a weaker interaction. Finally individual components can be measured by a Rf value or a Retaining factor value. This zero to one value measures the distance traveled by an individual component divided by the solvent front at which the solvent process had been terminated.

Procedure:

        First in this experiment the TLC chamber was prepared on the lab bench, this included a prepared solvent of an 8:2 ratio of dichloromethane and ethanol. Ten milliliters of this solution was prepared and placed in the chamber so about 1centimeter of the chambers base was covered with solvent. The cap of the chamber was screwed on and the solvent was shaken then the cap was unscrewed to release the gas. Then a sample was prepared of black sharpie marker and acetone on a watch glass.  The TLC plate was prepared with the Sharpie/Acetone mix by using a capillary to pick up and placed the mixture 1.5 centimeters from the bottom of the plate in three separated spots. The three dots had different concentrations using 1 drop from the capillary, 2 drops, or three drops. Once prepared the TLC strip was placed into the chamber and the cap was sealed on. From here the chamber and plate was undisturbed until the solvent had run up 80% of the plate. From here the TLC plate was removed with tweezers and marked at where the solvent front had reached before letting dry. TLC plated were then analyzed with UV light and marked at positions of varying compounds. Appearance was recorded as well as Rf values were calculated for each of the spots identified as components. The TLC plate was drawn in the lab notebook. This procedure was then completely repeated twice with a 6:4 mixture of dichloromethane/ethanol and a 4:6 mixture of dichloromethane/ethanol, where appearances were detailed, drawn, and Rf values were calculated. Finally all compounds were disposed of properly and all glassware and other materials used were cleaned and put away.

Results:

Table 1.1

Discussion:

        Our results showed the separation of various compounds found within a sharpie marker mixed with acetone when placed in a chamber with a dichloromethane/ethanol solvent mixture. Our first trial found 9 compounds revealed by UV light. Colors of the compounds varied from black, grey, yellow and purple and were found to be symmetrical with the other concentrations on the TLC plate, the only difference being that some colors were thicker and more vivid on high concentrations then those on lower concentrations. Rf values found that the most polar compound had a retention factor of 0.45 and the most non-polar compound had a retention factor of 0.99. In our second trial with a 6:4 mixture, 6 dots were obtained with colors similar to the first trial. This mixture was slightly less polar due to the increase in Dichloromethane and increase in ethanol concentration. With our most polar value being 0.69 and least polar value being at 0.97. Our third trial with a 4:6 mixture, 5 dots were obtained. This mixture was even less polar with our most polar Rf value at 0.73 and our least polar at 0.98.