Only the AMD procedure can be successfully employed for reproducible gradient elution with silica gel as the stationary phase. In column liquid chromatography, gradient elution is common on reversed phases only because a silica gel column would call for a time consuming reconditioning or be irreversibly degraded, which is not acceptable in a technique depending on multiple use of the stationary phase. In thin-layer chromatography this is not relevant.
The principle of the CAMAG AMD procedure
The HPTLC plate is developed repeatedly in the same direction
Each successive run extends over a longer solvent migration distance than the one before.
Between runs, the solvent is completely removed from the developing chamber and the layer is dried under vacuum.
Each successive run uses a solvent of lower elution strength than that of the one used before. In this way, a stepwise elution gradient is formed.
The combination of focusing effect and gradient elution results in extremely narrow bands. Their typical peak width is about 1 mm. This means that, with the available separation distance of 80 mm, up to 40 components can be completely resolved, i.e. with base line separation.
Key features of the AMD 2 at a glance:
Multiple development, gradient elution
Separation power improved over regular HPTLC by a factor 3
Data input and monitoring through winCATS
Utilizing time also after working hours
Compliant with requirements of GMP/GLP
Installation Qualification (IQ) and Operation Qualification (OQ) provided
Usage in a 21 CFR Part 11 environment under winCATS.
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