Silica gel high-performance

C. E. Poole and M. T. Belay, The influence of layer thickness on the cliromatographic and optical properties of high performance silica gel tliin layer cliromatographic plates , J. Planar Chromatogr. 4 345-359 (1991). 

Plates. High performance silica gel (10 x 20 cm) with fluorescent indicator and concentration zone (see Reagent Appendix). 

The USP 24/NF 19, section 201 (Ref.f p. 1856), contains a general TLC identification test that involves a non-high-performance silica gel layer with fluorescent indicator, chloroform-methanol-water (180 15 1) mobile phase, and detection under 254 nm UV light for verification of the identities of compendial drugs in dosage form test solutions prepared according to the individual monographs. Section 621 of the USP 24/NF 19 (Ref. pp. 1916-1917) presents brief information... 

Layer Channeled preadsorbent high-performance silica gel. 

Aloisi, J. D., Sherma, J. and Fried, B. (1990) Comparison of mobile phases for separation and quantification of lipids by one-dimensional TLC on preadsorbent high performance silica gel plates. Journal of Liquid Chromatography, 13, 3949-72. 

Figure 10.7 HPTLC separation of 1, acetophenazine 2, perphenazine 3, trifluoroperazine 4, promazine 5, thioridazine and 6, chlorpromazine on a high-performance silica gel plate using multiple development in the mobile phase benzene-acetone-ammonium hydroxide (80 20 0.2). [Reproduced with permission of The American Association for Clinical Chemistry from Fenimore et al. (1978).]...

Norfolk, E., Khan, S. H., Fried, B., and Sherma, J. (1994). Comparison of amino acid separations on high performance silica gel, cellulose, and C-18 reversed pha.se layers and application of HPTLC to the determination of amino acids in Biomphalaria glahrata snails. J. Liq. Chromatogr. 17 1317—1326. 

Unidimensional TLC of nucleic acid derivatives has also been done on silica gel. Issaq et al. (1977) separated mixtures of alkylated guanines, adenines, uracils, and cytosines on silica gel 6OF2S4, in various chloroform-alcohol solvent systems. The addition of 1 ml of ammonium hydroxide to the mobile phase prevented streaking and resulted in nondistorted developed spots. Figueira and Ri-beiro (1983) separated adenine, adenosine, inosine, hypoxanthine, 2-AMP, 5-AMP, ADP, ATP, cAMP, and dibutyryl cAMP also on silica gel 6OF254, and Sleckman et al. (1985) used conventional and high-performance silica gel to separate four representative nucleotides and their corresponding nucleosides. Detailed Experiment 2 of this chapter describes a unidimensional separation of nucleotides and nucleosides on silica gel. 

Brinkman and deVries (1979, 1980) also described TLC applications of drugs on high-performance silica gel plates. Numerous separations of pharmaceuticals on Whatman HPTLC plates and a useful list of references of drugs separated by HPTLC have been presented in the Whatman TLC Technical Series, Volume 2. 

A, Baker Flex cellulose sheets B, Baker Flex microcrystalline cellulose sheets C, Whatman K6 silica gel plates D. Whatman high-performance silica gel plates E, Fixion ion-exchange sheets (Na form). FXa, no prior treatment FXs. layer preequilibrated with equilibration buffer for 16 h FXc, layer preequilibrated as for FXb but at 45 C. Solvent for A, B, C, D, 2-butanol-acetic acid-water (3 1 1) solvent for E and run buffer, 84 g citric acid + 16 g NaOH + 5.8 g NaCl + 54 g ethylene glycol+4 ml cone. HCl (pH 3.3) solvent equilibration buffer, run buffer diluted 30 times (pH 3.8). S ce From Ref. 69. 

A stock cholesterol (99.9% purity) solution was prepared at a concentration of 1 mg/ml in chloroform the TLC standard was prepared by a 10-fold dilution with chloroform (100 ng/)tl). Whatman LHPKDF 20 x 10 cm channeled high-performance silica gel plates with preadsorbent spotting area for quantitative densitometry, and Whatman PK1F 20 x 20 cm plates with 0.5-mm silica gel layer thickness for preparative TLC were used. Layers were cleaned by predevelopment with... 

An ion-pair reagent was not wholly essential for separation, and it was found that the optimum concentration was probably below 0.01 mole/liter. Different chain lengths up to C4 caused minor modifications in the order of / / values for the eight acids. For the aromatic dicarboxylic acids in chloroform-tetrahydrofuran (2 1) on silufol (175), the Ry order found was isophthalic (0.5), terephtha-lic acid (0.49), 2-hydroxyethyl isophthalate (0.33), 2-hydroxyethyl-terephthalate (0.35), and the bis ester (both 0.18). Cj and cyanopropyl-bonded high performance silica gel layers in conjunction with ion-pair reagents have been employed to separate dihydroxybenzoic acids (175a,175b). 

Probably, isomers are also included in the 14 oxidation products of retinyl acetate separated on preparative silica gel HR plates developed with n-hexane diethyl ether (95 5 to 10 90, depending on the polarities of the substances to be separated) (14). After the first TLC run, five fractions are obtained which are subfractionated in a second run. However, no positive identification is given by the authors. Another separation of isomers is described by DePaolis (IS). On high-performance silica gel plates eluted with diethyl ether-cyclohexane-acetone-glacial acetic acid (40 60 2 1, by vol) all-trans- and 13-cis-retinoic acid were separated and quantitated in gel formulations. Cream samples, however, contained some interfering excipients and required two-phase (reversed-phase Cig and normal-phase silica gel) two-dimensional TLC. This will be discussed in the section of reversed phase TLC. 

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