Báo cáo sắc ký bản mỏng TLC (1)

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

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

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.

As the mobile phase rises up the TLC plate

by capillary action, the components dissolve

in the solvent and move up the TLC plate.

Individual components move up at different rates, depending on intermolecular forces

between the component and the silica gel

stationary phase and the mobile phase

Stationary

phase

mobile phase

Principle

The stationary phase is a

powdered adsorbent which

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.

Deposition of the sample

Developing the plate

Identifying the spots

TLC technology

Deposition of the sample

Video

How do you do for a good

deposition ?

- 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)

Deposition of the sample

Developing the plate

Which steps do you do to

develop the plate?

Video

- 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 has been deposited must be above the level of the solvent

Developing the plate

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…).

 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

R f 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:

o

f

x

x front

solvent

by the run

Distance

solute

by the run

Distance

1 Calculate the Rf of 4 compounds.

2 How many components are there in

the unknown?

 Analyzing the purity of a compound.

 Following the course of a reaction.

 Identification of components of a

mixture (using appropriate standards).

Advantage & Disadvantage

by the run

Distance

solute

by the run

Distance

1 Predict what will happen when this plate is developed in the chamber ?

Answer

The samples were spotted too low on the plate, and the chamber is too full with the developing solvent Therefore, when the plate is placed into the chamber, the spots will bleed off of the plate and into the solvent The plate cannot be developed

2 What is wrong with the plate shown below?

Answer

The samples were spotted on the plate

development of the plate, the spots will run together, causing inconclusive experimental results

3 A student removed this chromatogram from

the development chamber and allowed the

solvent to dry What did he forget to do?

Answer

The student forgot to trace the solvent front before allowing the solvent to dry on the chromatogram No Rf values can be calculated from this chromatogram.

4 What is wrong with this student's paper

chromatography chamber setup?

Answer

The chamber is uncovered, so it is not

saturated with solvent vapor

5 Consider the following silica gel TLC plate

of compounds A, B, and C developed in hexane Which compound, A, B, or C, is the most polar?

Answer

Compound A is the most polar because

it does not travel as far as the other two compounds

Thanks for your attention !!!