Tlc

THIN LAYER CHROMATOGRAPHY

1. THIN LAYER CHROMATOGRAPHY

2. Contents Introduction History Principle TLC System component R f value Application Pros & Cons of TLC

3. Introduction Chromatography is a technique for the separation of a mixture by passing it in solution or suspension through a medium in which the components move at different rates. Thin Layer Chromatography is a type of chromatography in which compounds are separated on a thin layer of adsorbent material, typically a coating of silica gel on a glass plate or plastic sheet.

4. History

5. History Chromatography was first used in Russia by the Italian-born scientist Mikhail Tsvet in 1903. Martin and Synge developed partition chromatography to separate chemicals with only slight differences in partition coefficients between two liquid solvents. The first reported use of a thin layer was in 1938 by two Russian scientists, N.A. Izmailov and M.S. Schreiber.

6. Principle T hin-layer chromatography depends on the separation principle. The separation relies on the relative affinity of compounds towards both the phases. The compounds in the mobile phase move over the surface of the stationary phase. The movement occurs in such a way that the compounds which have a higher affinity to the stationary phase move slowly while the other compounds travel fast. Therefore, the  separation of the mixture  is attained. On completion of the separation process, the individual components from the mixture appear as spots at respective levels on the plates. Their character and nature are identified by suitable detection techniques.

7. TLC System Component TLC plates , preferably ready-made with a stationary phase: These are stable and chemically inert plates, where a thin layer of stationary phase is applied on its whole surface layer. The stationary phase on the plates is of uniform thickness and is in fine particle size. TLC chamber  This is used for the development of the TLC plate. The chamber maintains a stable environment inside for proper development of spots. It also prevents the evaporation of solvents and keeps the process dust-free. Mobile phase  This comprises of a solvent or solvent mixture. The mobile phase used should be particulate-free and of the highest purity for proper development of TLC spots. The solvents recommended are chemically inert with the sample, a stationary phase. A filter paper This is moistened in the mobile phase, to be placed inside the chamber. This helps develop a uniform rise in a mobile phase over the length of the stationary phase. owlcation.com

8. Procedure With a pencil, a thin mark is made at the bottom of the plate to apply the sample spots. Then, samples solutions are applied on the spots marked on the line in equal distances. The mobile phase is poured into the TLC chamber to a leveled few centimeters above the chamber bottom. A moistened filter paper in the mobile phase is placed on the inner wall of the chamber to maintain equal humidity. Now, the plate prepared with sample spotting is placed in the TLC chamber so that the side of the plate with the sample line is facing the mobile phase. Then the chamber is closed with a lid. The plate is then immersed, such that the sample spots are well above the level of mobile phase for development. Allow sufficient time for the development of spots. Then remove the plates and allow them to dry. The sample spots can be seen in UV light chamber or any other methods as recommended for the said sample. microbenotes.com

9. Retention Factor (R f ) value It is the ratio of distance travelled by a substance to distance travelled by a solvent front. Higher the R f value lesser the polarity of the substance. Lower the R f value higher is the polarity of the substance. The R f value is calculated using the following equation:- R f = distance the spot has moved /distance solvent front moved orgchemboulder.com

10. Applications To check the purity of the given samples. Identification of compounds like acids, alcohols, proteins, alkaloids, amines, antibiotics, and more. To evaluate the reaction process by assessment of intermediates, reaction course, and so forth. To purify samples, i.e., for the purification process. To keep a check on the performance of other separation processes. Being a semi-quantitative technique, TLC is used more for rapid qualitative measurements than for quantitative purposes. But due to its rapidity of results, easy handling, and inexpensive procedure, it finds its application as one of the most widely used chromatography techniques.

11. Advantages It is a simple process with short development time. It helps with the visualization of separated compound spots easily. The method helps to identify the individual compounds. It helps in isolating of most of the compounds. The separation process is faster and the selectivity for compounds is higher (even small differences in chemistry is enough for clear separation). The purity standards of the given sample can be assessed easily. It is a cheaper chromatographic technique.

12. Disadvantages Thin Layer Chromatography plates do not have longer stationary phase. When compared to other chromatographic techniques the length of separation is limited. The results generated from TLC are difficult to reproduce. Since TLC operates as an open system, some factors such as humidity and temperature can be consequences to the final outcome of the chromatogram. The detection limit is high and therefore if you want a lower detection limit, you cannot use TLC. It is only a qualitative analysis technique and not quantitative.

13. Conclusion In conclusion thin layer chromatography is a useful technique when trying to identify compounds and see how they separate. It is also a useful tool to see how polar or nonpolar a compound is. A s the mobile phase rose up on the TLC plate it dragged the ink from the marked dot up along the TLC plate. The pigment that was closer to the marked dot was more attracted to the stationary phase. The pigment that traveled the farthest up on the TLC plate more attracted to the mobile phase, and solvent.

14. References www.merckmillipore.com www.owlcation.com www.microbenotes.com www.chemistryhall.com www.coursehero.com