Layer Chromatography Ink Analysis Thin Layer Chromatography

¶ … Layer Chromatography

Ink Analysis Thin Layer Chromatography (TLC)

Ink analysis has been known as the most significant process that is capable to divulge important information on queried documents. It is clear that inks are manufactured from an extensive variety of substances that tend to demonstrate extremely dissimilar reactions chemically. Due to the manner in which documents are important and it destruction is not containable, there has been a method that has been explored as the most potential means of differentiation of ink samples and this method is known as thin layer chromatography. This report is going to take us through the process of ink analysis by Thin Layer Chromatography which will be done in a Laboratory and the whole process is going to be demonstrated in the course of the paper. The report will also outline the background of thin layer chromatography highlighting its history as well as braking down how the method works looking at each and every procedure. Report will also display the observations of the entire procedure finalizing with a conclusion.

Introduction

According to Harry W. Lewis, Christopher J. And Moody, (Illustrated edition ed) thin layer chromatography (TLC) is a technique of chromatography mainly used to separate mixtures. This is done on a glass sheet, plastic or aluminium foil and whatever is picked must be coated with a thin layer of permeable material which in many occasions is silica gel, cellulose or aluminium oxide. Stationary phase is the name given to this permeable layer. It is important to note that all types of chromatography work on the similar principal and they all bear a solid or a liquid supported on a solid otherwise known as stationary phase as well as a liquid or a gas otherwise known as a mobile phase. There is a flow of mobile phase through a stationary phase carrying with it the mixture of components. We also have to note that different components travel at different rates.

Monitoring the progress of a reaction, identifying compounds present in a particular mixture as well as determining the purity of a substance can be done using a thin layer chromatography e.g. detecting pesticides or insecticides in water or food and analyzing the dye composition of fibers in forensics among many others (Reich, E.; Schibli A. 2007).

Materials and Methods

Materials that will be needed are a Thin Layer Chromatography plate, paper Chromatography strips, Beakers with lids, Test tubes with tops, Butonal, 2 Butonal, Acetic Acid, Methanol, Ammonia, Water, Leaf Green dye mixture, Caramel dye mixture, Brilliant Blue dye, Golden yellow dye, Lilac dye mixture, Forest green dye and finally Yellow 135 dye.

Preparation of a plate

It is of importance to know that TLC plates are available commercially with standard element variety in sizes purposely to advance reproducibility. The preparation is done by mixing the adsorbent with a tiny amount of inert binder plus water. The mixture is then spread as a thick slurry on an unreactive carrier sheet which many at times is a glass, plastic or aluminium foil. The resultant plate is then dried and activated through heating in an oven for about 30 minutes at a temperature of about 110 degrees cellcious. 0.1 -- 0.25 mm are suppose to be the thickness of the absorbent layer purposely for analysis and 0.5 -- 2.0 mm for preparative TLC.

The following procedure is essential while running a thin layer chromatography:

1. A diminutive spot of solution holding the sample was applied to a plate 1.5 cm from the underneath edge. The solvent was then given time to completely evaporate off, this was done to bring about efficiency in the result. In the event that a non-volatile solvent was used in sample application then the plate had to be dried in a vacuum chamber.

2. With a help of what we call separation chamber which in this was a beaker (glass), a little portion of an elutant was poured in it to a depth of about 1cm. In that chamber we also placed a strip of filter paper in a manner that its bottom touches the solvent and the paper had to lie on the wall of the chamber and reaches almost to the top of the beaker. The container was then bunged with a cover and was left for a small number of minutes to allow the solvent vapours climb the filter paper and saturate the air within the chamber. It is good to note that if the chamber is not saturated then poor separation as well as non-reproducible result may be experienced.

3. The TLC plate was then placed in the chamber in a way that the spot of the sample never gets to contact with surface of the elutant which is in the chamber and the chamber is again closed. The solvent travels up the plate through capillary action as it meets the sample mixture and carries it up the plate. The plate was then removed and dried the minute the solvent front got in touch with not elevated than the top of the filter paper in the chamber.

Observation

The distance travelled by the solvent which is otherwise known as the measurement is taken from the plate purposely to assist in identification of the compound present. The moment the solvent front gets close to the top of the plate, the plate is then removed from the beaker as the position of the solvent is marked with another line prior to its evaporation and the measurements are then recorded. The working formula for Rf value for each dye therefore becomes:

Rf = distance travelled by component

Distance travelled by solvent

Like in our case, the yellow component travelled 1.7 cm the base line and on the other hand the solvent travelled 5.0 cm. working out the Rf value of the yellow dye is:

Rf = 1.7

5.0

= 0.034

If a repeat of the experiment could be undertaken with exactly same conditions then the Rf values for every dye would always remain the same in that the value of the yellow dye would always remain 0.034.