GAS LIQUID CHROMATOGRAPHY (GLC)
One of the most difficult and frustrating problems ever encountered in the domain of pharmaceutical analysis is that of the simultaneous separation, identification and above all the quantitation of more than one compound from a complex mixture in a pharmaceutical product.
A good of sophisticated chromatographic techniques of separation have been put forward since early fifties that may be categorized into the following four groups, namely :
(a) Gas-Solid adsorption Chromatography (GSC),
(b) Gas-Liquid partition Chromatography, (GLC),
(c) Liquid-Solid adsorption Chromatography (LSC), and
(d) Liquid-Liquid partition Chromatography (LLC).
The first two groups have been collectively termed as ‘Gas Chromatography’. Its phenomenal growth at almost logarithmic pace may be attributed to its unparalleled potential in resolving components of a complex mixture. Gas chromatography fundamentally is a separation technique that not only essentially provides prima facie indentification of a compound but also caters for quantitative estimation after due calibration.
Gas chromatography makes use, as the stationary phase, a glass or metal column filled either with a powdered adsorbent or a non-volatile liquid coated on a non-adsorbent powder. The mobile-phase consists of an inert-gas loaded with the vapourised mixture of solutes flowing through the stationary phase at a suitable temperature. In the course of the passage of the vapour of the sample through the column, separation of the components of the sample occurs in two ways, namely :
(a) due to adsorption effects-i.e., when the prepared column consists of particles of adsorbent only, and
(b) due to partition effects-i.e., when the particles of adsorbent are coated with a liquid that forms a stationary phase.
Martin and Synge in 1952, became the Nobel Laureates for their excellent, innovative research work on the development of partition chromatography.
It is, however, pertinent to mention here that GLC has a much greater application in the field of pharma-ceutical analysis which extends over to most organic constituents that have a measurable vapour present at the temperature employed.
The principal advantages of GC are enumerated below, namely :
· It has high frequency of separation and even complex mixtures may be adequately resolved into constituents,
· It has a very high degree of sensitivity in detection of components i.e., only a few mg of sample is enough for complete analysis,
· Speed of analysis is quite rapid,
· Gives reasonably good accuracy and precision,
· The technique is fairly suitable for routine analysis because its operation and related calculations do not require highly skilled personnel, and
The overall cost of equipment is comparatively low and its life is generally long.