Impregnated reagents

Many studies have been recently focused on impregnated plates. The methods used for impregnation depend on whether the plates are home-made or commercially available. In the first case, the impregnation reagent is usually added to a slurry of the adsorbent, whereas ready-to-use plates are dipped in the solution of the reagent. 

Bhushan, R. Martens, J. Thuku Thiongo, G. Direct thin layer chromatography enantioresolution of some basic DL-amino acids using a pharmaceutical industry waste as chiral impregnating reagent. J. Pharm. Biomed. Anal. 2000, 21, 1143-1147. 

Different procedures have been used to study the extractant retention on the polymeric support as a result of these weak extractant-support interactions. In all cases the retention process has been studied using the analysis of the distribution isotherm of the impregnated reagent between water and a solid phase. Because of the complex nature of the resins no precise assumptions were made about the kind of adsorption sites, and the adsorption model used in the approach was the classical Branauer, Emmet, and Teller... 

Diatomaceous earth is a nonsorbent silica gel formed under the oceans from the skeletons of diatoms millennia ago. Its main use is on preadsorbent zone plates described previously. Prepared TLC layers of this material are available to hold impregnated reagents for special applications. 

The same method has been used successfully to prepare plates with silica gel, silica gel-polyamide, cellulose, and these adsorbents impregnated with a variety of reagents including HDEHP, TOPO, 8-hydroxyquinoline, dibenzoyl methane, and several metal salts (13-30). Brucine (20) and tartaric acid (22) were also mixed in slurries of silica gel as impregnating reagents to resolve enantiomers of amino... 

Separation data provided for various concentrations of each of the impregnating reagent. 

Bhushan, R. and C. Agarwal, Direct enantiomeric TLC resolution of DL-p>enicillamine using (R)-mandelic acid and L-tartaric acid as chiral impregnating reagents and as chiral mobile phase additive. Biomed. Chromatogr., 2008. 22(11) 1237-1242. 

With respect to the effect of the impregnating reagent concentration, no resolution was obtained for tested racemates when L-serine was increased or decreased to 0.2 or 0.05 g, respectively. 

Bhushan, R., Martens, J., Walbaum, S., Joshi, S. and Parshad, V., TLC resolution of enantiomers of amino acids and dansyl derivatives using (IR, 3R, 5R) 2-azabicyclo [3.3.0]octan-3-carboxylic acid as impregnating reagent, Biomed. Chromatogr., 11, 286-288, 1997. 

Different chiral selectors have been used for TLC resolution of variety of racemates of amino acids into enantiomers. Bhushan and Martens [20] in a review summarized various chiral selectors used as impregnating reagents, along with the mobile phases used for resolution of DL-amino acids (Table 12.2). 

Mixing of the impregnating reagent, say a chiral selector, with the silica gel prior to plate making, is one of the various methods used for impregnation and has successfully been used in the author s laboratory. 

The chemical nature of the impregnating agent and the structure of the compounds being separated, along with the influence of the impregnating reagent on the... 

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