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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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Pharmaceuticals and Drugs
Table 1 (Continued)
Properties Advantage Disadvantage
Development mode Wide range
Chamber saturation Limited
Time requirement Fast
Dynamic modification
With organic solvent Generally used
With additives Good alternative
7. Detection possibilities
In situ detection
Visual Qualitative good Quantitative problematic
Densitometry without de Widely used
Densitometry after derivati Widely used
Spot elution Problematic
8. Applicability (see Table 2 for data)
9. Quantitation-validation
Method Problematic
System Problematic
Accuracy Good
Selectivity Good
Limit of detection Good
Limit of quantitation Good
Linearity and range Limited
Plate loadability Good
Sample stability Problematic
Plate to plate variation Problematic
Sample concentration Good
Sample size Problematic
Spot type Problematic
Chamber type Problematic
Upvalue Problematic
Color reaction Problematic
Detection Good
Mobile phase composition Good
Temperature Problematic
Running distance Good
Szepesi and Nyiredy
B. Sensitivity to Experimental Conditions
Planar chromatographic methods are more or less sensitive to changes in the environmental conditions. Small changes in the eluent composition and/or in temperature and relative humidity during development may cause dramatic changes in the retention characteristics of the compounds being separated. This effect is more pronounced and valid if unsaturated chambers are used for development. Similarly, the quality of any capillary action chromatographic separation is a function of the type and size of the developing chambers.
C. Stationary Phase Selection
The most important stationary phases used in pharmaceutical analysis can be found in text books (22, 23). Modifications have been done to improve the selectivity and efficiency of precoated layers in TLC. The following examples of modifications could be generally applied in the pharmaceutical analysis:
Bare silica and alumina
Precoated layers suitable for high-performance TLC (HPTLC)
Combinations of different sorbents on a precoated layer
Hydrophobic and hydrophilic modification of bulk sorbents and precoated layers More detailed treatment of this topic will be given in Section III. A.
D. Mobile Phase Selection
The correct choice of mobile phase composition for a given separation constitutes an important stage in achieving good separation by TLC. The basic strategy of mobile phase selection in TLC is similar to HPLC regarding solvent classification and elutropic series (24-27). In general, the selection of a particular solvent to be used is simpler; it must be pure having relatively low boiling point and viscosity, cheap and compatible with the sorbent, support plate, and binder. Selection of appropriate mobile phase composition is more difficult. A great variety of factors can be adjusted, e.g., the solvent components, their relative concentration, pH, solvent strength, etc. A more detailed explanation will be given in Section III.C.
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