Hydrophilic modification, precoated plates

The recently introduced hydrophilic modified precoated plates have broadened the spectrum of selectivity available for TLC. These plates are referred to as HPTLC-NH2 precoated plates, in which > -aminopropyl groups are bonded to the surface of a silica-gel skeleton, and HPTLC-CN precoated plates. with cyanopropyl moieties as the functional groups. In terms of polarity the two hydrophilic modifications can be classified as follows Normal Si02 > NH2 > CN > RP. Since the surface NHv and CN groups are of medium polarity, no wetting problems are encountered with the corresponding plates even at the maximum level... 

Reversed-phase PLC precoated plates are based on silica gel matrices with chemical modifications in such a manner that the accessible polar, hydrophilic silanol groups at the silica gel surface are replaced by nonpolar, hydrophobic alkyl chains via silicon-carbon bonds. For preparative purposes, up to now only PLC precoated RP plates with C-18 modification are available. This abbreviation is often also designated as RP-18, meaning that an octadecyl alkyl chain is chemically bonded to the silica gel surface. 

Figure B The influence of different hydrophilic modifications on /(/values of steriods. Plates HPTLC precoated plate NH2 F254s, DIOL F254s, CN F254s. Eluents a. straight-phase system, petroleum benzine (40-60°C) cetone 80/20 (v/v) b. reversed-phase system, acetone/water 60/40 (v/v). Migration distance 7 cm. Chamber normal chamber without chamber saturation. Compounds , cortisone A, corticosterone , cortexone. Detection UV 254 nm.

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