Báo cáo sắc ký bản mỏng TLC (1)

TLC


Thin Layer chromatography


Which method can be used to evaluate an analyte based on a
titrant?

T

I

T

R

A

T

I

O

N



1. Principle
2. TLC technology

3. Rf value

4. Application

Outline


Principle
In TLC, components of the mixture are partitioned between
an adsorbent (the stationary phase, usually silica gel, SiO2)
and a solvent (the mobile phase) which flows through the
adsorbent.


Individual components move up at different rates, depending on

As the mobile phase rises up the TLC plate by capillary action, the
intermolecular forces between the component and the silica gel

components dissolve in the solvent and move up the TLC plate.
stationary phase and the mobile phase.


Principle
Analyte

Stationary phase

mobile

phase


Stationary phase

The stationary phase is a powdered
adsorbent which is fixed to a aluminum,
glass, or plastic plate.

 They are polar stationary phase.


Which conclusions can be drawn from the
polarity of the stationary?


 More polar analytes interact more strongly with the stationary
phase in move very slowly up the TLC plate.

 More nonpolar analytes interact less strongly with the polar silica
gel and more strongly with the less polar mobile phase and move
higher up the TLC plate.

attached video ???


Mobile phase

The mobile phase is an organic solvent or a mixture of
organic solvents which is less polar than the stationary phase.

TLC technology
Deposition of the sample

Developing the plate

Identifying the spots


Deposition of the sample

How do you do for a good deposition ?

Video


Deposition of the sample

-

A small volume of sample will be dissolved in a volatile

solvent

- Using the capillary, deposited it close to the bottom of the
plate as a small spot (d = 1-2mm)


Developing the plate

Which steps do you do to develop the plate?

Video


Developing the plate

- The plate is placed in a glass developing chamber that contains a
small amount of the appropriate developing solvent

- The chamber is then covered
- The position at which the sample
above the level of the solvent

has been deposited must be


Identifying the spots

How do you visualize the spots?

Video


Identifying the spots

-

If there are any colored spots, circle them lightly with a pencil.

Most samples are not colored and need to be visualized with a
UV lamp (or iodine chamber, KMnO4 solution…).


Note
 If the TLC plate runs samples which are too concentrated, the spots
will be streaked and/or run together. If this happens, you will have to
start over with a more dilute sample to spot and run on a TLC plate.


Rf value
The Rf value is the “ retardation factor” or the “ ratio-to-front” value
expressed as a decimal fraction.
The Rf value can be calculated as:

Distance run by the solute
x
Rf =
=
Distance run by the solvent front x o


Rf value

Rf = x1/xo
xo

x1

0 < Rf < 1

Example

1.

Calculate the Rf of 4 compounds.

2.

How many components are there in the unknown?


Solution
Rf (A) = 2/5 = 0.4
Rf (B) = 3/5 = 0.6
Rf (C) = 0.8/5 = 0.16
Rf (D) = 4/5 = 0.8
=> The unknown contains 2 compounds: C and B


Application
 Analyzing the purity of a compound.
 Following the course of a reaction.
 Identification of components of a mixture (using appropriate
standards).