Amino-modified precoated silica layers

Amino-modified precoated silica layers In the case of the NH2-modified precoated layers, the amino group is bonded via a propyl group as a spacer onto the silica gel. Besides their use in a straight-and a reversed-phase retention mechanism, a further possibility is application in ion-exchange chromatography. This special use is described in Section III.A.3. Typical applications with amino-modified precoated layers used in straight- or reversed-phase mechanisms are, among others, separations of barbiturates and steroids (142, 143), carbohydrates (144-146), phenols and xanthin derivatives (147). and purines and pyrimidines (148,149). 

Amino acids and their derivatives] resolution of amino acids and dieir derivatives on impregnated layers, 406-408 resolution of enantiomeric mixtures of amino acids and their derivatives, 411-419 separation of amino acid derivatives, 398-406 DABITC derivatives of amino acids, 403-406 dansyl amino acids, 402 dinitrophenyl-amino acids, 406 PTH amino acids, 399-402 separation of amino acids, 389-398 chromatographic techniques, 393-395 preparation of test materials, 389-392 TLC system for amino acids, 395-398 Aminoglycosides, 457-461 Amino-modified precoated silica layers, 114,117-119... 

AMINO-, CYANO-, AND DIOL-MODIFIED PRECOATED SILICA LAYERS... 

Amino-, Cyano-, and Diol-Modified Precoated Silica Layers... 

In Vol. lb of the reagent books, Jork et al. describe and hypothesize about the reactions that take place in thermochemical activation, the term used for this physical process, and give the conditions for the thermal treatment of a large number of substances on aluminum oxide gel, silica gel and amino-modified sihca gel precoated layers. 

An improvement in the use of phases impregnated with Pirkle selectors in planar chromatography was proposed by Witherow et al. [48], which prepared a two-phase modified amino-bonded stationary phase by immersing the lower portion of the precoated silica gel 60 HPTLC NH2 F254S plate (Merck) in a solution of CS2. The layer portion ionically modified with the chiral selector was employed for the enantioseparation of the two aforementioned test materials. 

HPTLC separation material is available in the form of precoated layers supported by glass, plastic sheets or aluminum foil. Although precoated layers of aluminum oxide, cellulose, polyamide, ion exchange materials, reversed phase silica (alkyl bonded) have been commercially available for quite some time, the vast majority of TLC separations is carried out on normal phase silica gel, particularly in quantitative TLC analysis. Recently introduced plates modified with amino, cyano and diol functional groups bonded to the silica can be used as multimodal media. Depending on the developing solvent used, they extend normal phase or reversed phase chromatographic properties. These layers may affect the predominant role of normal phase silica gel in TLC to a certain extent. They are described in Chapter 4 of this book. Also chiral layers for the separation of optical isomers are available and cause increased interest (11). 

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