SUPER CRITICAL FLUID CHROMATOGRAPHY

BY ABIJAH

08171S0417

MPAQA

SUPER CRITICAL LIQUID CHROMATOGRAPHY

Def Introduction Principle Instrumentation Applications

Definition

Chromatography: It is a method of separation of complex mixtures .

Super critical liquid chromatography: It is a type of column chromatography in which super critical fluid is used as a mobile Phase for the separation of mixtures.

Super critical fluid: A super critical fluid is that which contains temperature and pressure above its critical temperature and pressure.

The critical temperature of a substance is the temperature above which a distinct liquid phase cannot exist regardless of pressure.

The critical pressure is that the vapour pressure at its critical temperature.

No matter how much temperature and pressure is applied the substance cannot exists as a liquid.

Introduction

This technique is a hybrid of Gas and High performance liquid chromatography.

It is relatively a recent chromatographic technique which is commercially available since 1982.

Advantages such as rapid separation without the use of organic solvents, faster separation than HPLC, high resolution chromatography than GC thereby faster analysis of thermo labile compounds.

Super critical temperature and pressure are the defining boundaries for a pure substance.

Beyond these boundaries the properties of a substances are intermediate between a liquid and gas.

In this region the fluid has a good solvating power and high diffusivity.

Instrumentation

An HPLC like setup with two reciprocating pumps designed to provide a mixed mobile phase with a packed analytical column placed in an oven followed by an optical detector in which the pressure and flow rates can be independently controlled .

A GC like setup with a syringe pump followed by a capillary column in a GC oven with a restrictor followed by a flame ionization detector, where the pressure is controlled by the flow rate of the pump.

In SFC the mobile phase is initially pumped as a liquid and is brought into the super critical region by heating it above super critical temperature before it enters the analytical column.

It passes through an injection valve where the sample is introduced into the super critical stream and then into the analytical column.

It is maintained supercritical as it passes through the column and into the detector by a pressure restrictor placed either after the detector or at the end of the column.

Restrictor prevents clogging Mobile phase: Carbon dioxide, ethane,

butane, nitrous oxide, dichlorodifluoromethane, diethyl ether, ammonia and tetrahydrofuran.

Reciprocating pumps Syringe pumps LC Injection valve (Pneumatically driven

valves) Conventional GC or LC ovens Capillary, stainless, Open tubular columns. Stationary phase: Fused silica

Detectors: Optical, Flame ionization detector, Spectroscopic detectors.

The results of a run in SFC are a chromatogram.

Example: Chromatogram of separation of polymers. It is schematically shown as follows.

Applications

Purification of thermo labile compounds. Characterization of polymers. Complex distributions can be resolved, low

temperatures can be used Oligomers can be detected. Solute diffusivities Separation of enantiomers

Metabolites of estrogens are separated by SFC .

Separation of chiral and Achiral mixtures. Natural products, drugs, foods, Pesticides

and herbicides, surfactants, fossil and propellants.