Types of Gas Chromatography

l Gas liquid chromatography GLCThe mechanism of separation is based upon the partition of the analyte between

gaseous M.F. and a liquid S.F. immobilized on the surface of an inert solid

l Gas solid chromatography GSC

GSC is based upon adsorption of gaseous substance on solid surfaces.

GLC Instrument

• Carrier gas supply ( M.F.)• Sample injection system

• Column configuration and column ovens• Detector systems• Readout systems

Size exclusion chromatography :

Subdivided into 1 - gel filtration2 – gel permeation chromatography

Use aqueous solvents and hydrophilic packings. nonpolar organic solvents and hydrophobic packings . Packing for size-exclusion chromatography consists of small silica or polymer particles containing a network of uniform pores into which solute and solvent molecules can diffuse .

Advantage of Size-Exclusion Chromatography

1 - Short separation time 2 - Good sensitivity 3 - Freedom from sample loss 4 - Absence of column deactivation

HPLC Instrument

1-Mobile-Phase Reservoirs One or more glass or stainless steel reservoirs

2-Pumping Systems

3-Sample Injection Systems: Syringe injection through a self-sealing elastomeric septum

4-Chromatographic Columns -Guard Columns Ø Remove impurities from solventØ Saturates mobile phase with liquid of stationary phase before the analytical column - Analytical Column Copper or stainless steel tubing straight, 15 to 150 cm in length; 2 to 3 mm packing - silica gel, alumina, ….

5-Column Thermostats

6-Detectors

Mechanisms of chromatography

n Adsorption A charge interaction occur between the active group of the sample and the sorbent S.F.

n Partition The separation depends upon the distribution of the compound of the mixture between the mobile phase and a liquid stationary phase according to partition coefficient value.

n Ion Exchange Ion exchange contains labile ions that are capable of exchanging with ions of the same change in the sample.

Ion-Exchange chromatography

Based upon exchange equilibria between ions in solution and ions of like sign on the surface of an insoluble , high-molecular-weight solid .

Clay and zeolites ,synthetic ion-exchange resins .

Formed during emulsion copolymerization of styrene and divinylbenzene.

The mobile phase are aqueous solutions that may contain moderate amount of methanol or other water-miscible organic solvents .