This method of separation is called gel, molecular sieve or size-exclusion mechanism of separation.

Size exclusionO

-O

O

O-

O-

O

A-2

B-

N+

N+

N+

N+

A-2

B-

Vertical ascending

A,BAB

Paper

Mobile phase

Tank

B A A,B

Vertical descending

A,BAB

Paper

Mobile phase

Horizontal

Analyte zone (A,B)

Paper

Mobile phase

Cotton piece

A B

The polar drugs are adsorbed temporarily on the polar stationary phase surface. The most common stationary phase used for this purpose is silica. Silica has a chemical composition similar to glass SiO2. xH2O

OH Si

OH

OH

OH

OH

Si

O

O

O

Si

OH

O

Si

OH

OH

Si

OHSi OH

Silicic acid

Silica

Adsorption

Partioning

OH

OH

CH3

CH3

CH3

CH3

m-Xylene Toluene

The carrier is a gas such as nitrogen or helium. The column is long to retain the

analyte longer and it is filled with polydimethylsiloxane particles or relevant

derivatives.

Si O SiO

CH3

CH3

CH3

CH3

Plastic cover

Stationary phase

Column pore

Capillary column

FID (flame ionisation detector)

+ ++ +

+++++

GC column

Flame

Ionised compounds

ECD (electron capture detector)

This detector has a radioactive element. The radioactive element can produce a rich field of electrons. Once the compounds contain electronegative elements such as halogens reach the electron field they will capture some of the electrons and this change in the electrical field will give a response proportion with the concentration of the halogenated analytes. This detector is widely used in the analysis of halocompounds such as pesticides and herbicides

Radioactive isotope

B-

B-

B-

B-

B- B

- B-

B-B

-B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-B

-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-