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Chromatographic scince series - Cazes J.

Cazes J. Chromatographic scince series - Marcel Dekker, 1996. - 1098 p.
ISBN 0-8247-9454-0
Download (direct link): ˝hromatography1996.pdf
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A literature search for the last 20 years indicates that extensive reviews on TLC systems for pharmaceuticals and drugs have been published (1 -9). Several monographs, review papers, and book chapters deal with the detection and quantitation of the separated compounds (5,6,10-14).
Governmental authorities generally require testing of pharmaceuticals for stability and impurity profiles before approval is given. Hence the monitoring of the stability of drugs by TLC under storage (15-17), and under stress (18,19) is of concern. In addition, determination of bulk active ingredient purity and of the impurity profile using TLC has been reported (4,5,20,21).
To illustrate the applicability of planar chromatographic methods in the pharmaceutical analysis a brief outline is given below. Some aspects are well known and will be treated briefly whereas others require a more detailed discussion. These aspects are listed in Table 1.
A. Ease of Operation
Conventional TLC is simple in instrumentation and in practice. The mobile phase can be easily prepared from organic solvents of conventional purity. The chromatograms can be visually evaluated after color reaction or under UV light. However, to yield quantitative results, densitometric evaluation is usually required. Although great efforts have been made to completely automate, this is difficult and not widely used.
Table 1 Advantageous and Disadvantageous Properties of Capillary Action Planar Chromatographic Methods
Properties Advantage Disadvantage
1. Ease of operation
Solvent selection Simple
Detection Off-line densitometry
Automation Difficult
Plate size Easy to select
2. Sensitivity to experimental conditions
Chromatographic parameters
Eluent composition Sensitive
Temperature Sensitive
Chamber type Sensitive
Chamber size Sensitive
Relative humidity Sensitive
Sample size No problem
3 . Stationary phase selection
Type of stationary phase More uniform
Nature of stationary phase Limited
Applicability Limited
Number of phases Wide range
Selectivity Limited in general use
4. Mobile phase selection
Separation selectivity Wide range
Variants in separation modes Limited
5. Separation efficiency
Plate efficiency Good
Peak symmetry Problematic
Irreversible absorption Frequently occurs
Solvent purity No problem
Spot shape Dependent
Spot size Dependent
Development modes Highly dependent
Vapor phase Highly dependent
6. Phase system optimization
Number of variables
Separation mode Limited
Stationary phase Limited
Mobile phase composition Wide range
Use of additives No problem
pH Limited
Temperature No
Relative humidity No
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