Answer

Thin Layer Chromatography

Introduction

Thin Layer Chromatography (TLC) is a method that is used in identification of different mixture compounds. TLC will tell the number of components that the mixture contains, compound identification, and the compounds purity. The reactions progress can also be monitored by the TLC as the as the appearance of product and disappearance of the reactants can be keenly observed.

TLC operations consist of the three steps that is spotting, development, and visualization. Unlike column chromatography, thin layer chromatography uses small samples. Although, thin layer chromatography uses small samples, it is usually accurate and the results obtained from a very efficient thin layer chromatograph is about 99% correct. For this reason, it has always been used to confirm the results obtained from column chromatography. The thin layer chromatography also takes a little time such that within 10 minutes, the results will have been obtained.

Thin layer chromatography is usually carried in the laboratory as a supplementary method. Although since its inception, there has been great progress because column chromatography has limited accuracy. Although column chromatography is an easy method of components separation, it has some setbacks that that limits its application; the results obtained from this technique are difficult to reproduce, the method is limited to soluble mixtures, it is difficult to obtain both qualitative and quantitative data from the results , thin layer chromatography works in an open system and maybe affected by humidity and temperature changes, separation takes place up to a given point because plate is limited, and the process is also not automatic.  TLC has two phases that is a stationary phase that is usually a solid and the liquid or gas mobile phase (Heinke 2017).  The stationary phase is normally a solid embedded on a glass, plastic, or aluminium plate while the liquid or gas phase is moving.

In this lab experiment, the stationary phase was made of silica gel while the mobile phase was composed of 99:1 ethyl acetate which is acetic acid. The chosen liquid is polar, this is because of the substances that needs to be separated are non-polar. Therefore, non-polar liquid like water could not be used. In this case, those substances that are polar will be attracted to the stationary phase and will tend to stick on the solid surface and will be spotted near the baseline while those that are non-polar will be eluded in the mobile phase. For the comparison to be done, retention factor (Rf) is usually calculated for every spot. This is done by dividing the distance travelled by the substance from the baseline to the distance travelled by the liquid mobile phase. The non-polar compounds will have higher retention factor compared to the polar substances. When the polarity of the solved is increased, the value of the retention factor increases while increasing the substance’s polarity results in lower Rf value.

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