Silica gels silanised

Precoated layers are available with chemically bonded phases. The most interesting group is silica gel in the reversed phase (both TLC and HPTLC) silica gel. silanised and with long chain hydrocarbons. The silanisation degree may be between 50 yf and 100%. In addition these layers can also be purchased in a water-compatible form. Water-compatible reversed-pha.se TLC may be used for separation at any water content of the eluent. 

Dibenzyl-14-crown-4 (lithium ionophore VI 6,6-dibenzyl-l,4,8,ll-tetra-oxa-cyclo-tetradecane) [106868-21-7] M 384.5, m 102-103°. Dissolve in CHCI3, wash with saturated aqueous NaCl, dry with MgSOa, evaporate and purify by chromatography on silica gel and gradient elution with C6Hg-MeOH followed by preparative reverse phase HPLC on an octadecyl silanised silica (ODS) column and eluting with MeOH. It can be crystd from MeOH (v Br 120 cm , C-O-C). [7 Chem Soc Perkin Trans 1 1945 1986.]... 

Beezhold and Stout [68] studied the effect of using mixed standards on the determination of PCBs. Mixtures of Arochlors 1254 and 1260 were used as comparison standards and gas chromatograms of these mixtures were compared with those obtained from a hexane extract of the sample after clean-up on a Florasil column. Polychlorinated biphenyls were separated from DDT and its analogues on a silica gel column activated for 17h and with 2% (w/w) of water added. The extracts were analysed on a silanised glass column packed with 5% DC-200 and 7.5% QF-1 on Gas Chrom Q (80-100 mesh) operated at 195°C with nitrogen as carrier gas (50-60mL min-1) and a tritium detector. 

Enhancement of a flexible PVC-silica composite interface was studied by the application of gamma-aminopropyltrimethoxysilane on silane. Composites containing silica and silanised silica up to 25.6 phr and prepared by sol-gel technology were subjected to water and water vapour attacks similar to that in their daily use. Silane application resulted in diminishing liquid water and water vapour sorption by about 24.0% and 11.9%, respectively. Inhibition of dioctyl phthalate migration from composites by silane application was also determined as 24% using UV measurements. 20 refs. TURKEY... 

The main use of TLC in analysis of amoxicillin and its formulated products is as an identity test. A major study [105] using silica gel and silanised silica gel plates with thirty five different mobile phases and iodine vapour detection produced a system, on silanised plates with ammonium acetate/acetone mobile phase, in which amoxicillin was separated from all the other penicillins studied. A slightly modified version of this system was subsequently introduced into the European and British Pharmacopoeia monographs for amoxicillin trihydrate and sodium salt [2]. The British [57,58] and US [9] Pharmacopoeias specify other TLC systems for identification of amoxicillin in formulated products. Simple TLC methods have been developed for identification of several compounds on the WHO essential drugs list, to help combat counterfeiting [106]. For amoxicillin, systems using ethyl acetate/acetic acid/water or acetone/toluene/acetic acid/water with silica gel plates were recommended. 

The scheme summarises all modern analytical and preparative chromatography protocols, such as high-performance liquid chromatography (HPLC) and gas-liquid chromatography (GLC), with all their conceivable variations. Reverse-phase HPLC or GLC , in which a non-polar liquid is adsorbed onto the solid - the stationary phase - is more appropriate for the analysis of mixtures of derivatives of amino acids and peptides. Cellulose in the above scheme would be replaced by a less-polar medium, such as acetylated cellulose, silanised silica gel, etc. in standard reversed-phase HPLC. 

Levarato has developed a series of quantitative methods for the determination of prednisolone along other corticoids after extraction from preparations and separation by TLC on silica gel plates and determination by spectrophotometric (absorption at 240 nm) or colorimetric methods (INH-hydrazone formation, tetrazolium reaction) (81). A simple, fast and quantitative TLC-method for the determination of prednisolone in tablets is described. The method is stability-indicating with respect to accuracy, specificity, sensitivity and precision. The coefficient of variation was between 1.26 and 1.96 % and the sensitivity was about 25 ng. The chromatographic separation was performed on a silicagel plate using two step development of the plate (82). A simple TLC method of separation of prednisolone from other corticosteroids is reported (83). Prednisolone and the dephosphorylated D-homosteroid can be separated on silanised silica gel TLC plates (36). 

Nonionics. The determination of nonionic surfactants using a silanised silica gel GF254 layer with aqueous 80% methanol and the use of a scanning densitometer at 525 nm for detection is described in [43]. Analysis of alkylphenol ethoxylates using a Kieselgel F60 layer with chloroform methanol as mobile phase and IR detection is described in [44]. 

The immobilisation of optically active alkenes on the silica surface by combined hydrosilation and sol-gel technology has been studied. The silanol and silyl groups in silicas which have been silylated with Cg chains have been estimated by Si NMR spectroscopy. Dehydroxylation and silanisation of the surfaces of sihca have been investigated. A A1 and Si NMR study of silane surface modified calcined kaolin has been reported. C NMR spectroscopy has been used to establish the bonding trihydrosilane to Ti02 particles. ... 

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