Phase aluminium oxide

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

Note The dipping solution can also be sprayed on. The detection of the aromatic acids is best performed on cellulose layers, if ammonia-containing mobile phases have been employed. The reagent can also be employed on silica gel, aluminium oxide, RP 18 and polyamide layers. 

The inorganic sorbents act as catalysts in all this [3,4]. Hie pH also probaUy plays a role. Reactions that do not otherwise occur are observed on add silka gd [3] or basic aluminium oxide layers. Reactions of this type have also been obsoved for amino [6-8] and RP phases [9]. The products of reaction are usually fluorescent and can normally be used for quantitative analysis since the reactions are reprodudble. 

The reagent can be used on silica gel, kieselguhr. Si 50000, aluminium oxide and RP layers amino phases are unsuitable. 

The reagent can be used most advantageously on aluminium oxide, silica gel, kieselguhr. Si 50000, cellulose, diol and water-wettable RP 18 layers there is less contrast in color on strongly hydrophobic RP 18 phases. NH2 and polyamide layers are not suitable because the iodine is too strongly bound and the whole layer is colored green-yellow. 

The reagent can be used, for example, on silica gel, kieselguhr and Si 50000 layers as well as on aluminium oxide, cellulose or chiral layers. Neither do difficulties occur on RP 18, Diol, NHj and CN phases. Silver nitrate- [4] and calcium oxalate-impregnated layers [9] are also suitable. However, polyamide phases are colored yellow. 

Note The reagent can be just as successfully employed on silica gel, kieselguhr, aluminium oxide and polyamide layers as it can with RP and NH2 phases. The final treatment with ammonia vapor to decolorize the background can be omitted in the last case. 

Owing to its excellent thermal and mechanical stability and its rich chemistry, alumina is the most widely used support in catalysis. Although aluminium oxide exists in various structures, only three phases are of interest, namely the nonporous, crys-tallographically ordered a-Al203, and the porous amorphous t]- and y-Al203. The latter is also used as a catalyst by itself, for example in the production of elemental sulfur from H2S (the Claus process), the alkylation of phenol or the dehydration of formic acid. 

A large range of stationary phases is available, and according to their polarity they can be divided into normal phase and reversed phase types. Silica gel, aluminium oxide, and a nitrile-bonded-phase are normal adsorbents used to separate carotenoids... 

Jameson, R. F. Salmon, J. E. (1954). Aluminium phosphates Phase-diagram and ion-exchange studies of the system aluminium oxide-phosphoric oxide-water at 25 °C. Journal of the Chemical Society, 4013-17. 

These have now been superseded by capillary columns, which offer greatly improved separation efficiency. Fused silica capillary tubes are used which have internal diameters ranging from 0.1 mm (small bore) to 0.53 mm (large bore) with typical lengths in excess of 20 m. The wall-coated open tubular (WCOT) columns have the internal surface of the tube coated with the liquid (stationary) phase and no particulate supporting medium is required. An alternative form of column is the porous-layer open tubular (PLOT) column, which has an internal coating of an adsorbent such as alumina (aluminium oxide) and various coatings. Microlitre sample volumes are used with these capillary columns and the injection port usually incorporates a stream splitter. 

The efficacy of various normal and RP-TLC systems for the separation of the colour pigments of Capsicum annuum was compared. Neutral aluminium oxide, silica gel, diatomaceous earth, silica gel-diatomaceous earth 1 1, cellulose, cyano, diol- and amino modified silicas were employed as stationary phases for adsorption TLC. Polyamide and modified silica layers were used for RP-TLC as received, the other stationary phases were impregnated by overnight predevelopment in n-hexane - paraffin oil, 95 5 v/v. 

Acid (pH 3) ammonium oxalate has been widely used to dissolve iron and aluminium oxides and release bound trace metals since its introduction in 1922 (Tamm, 1922) (Tamm s reagent). Typically McLaren et al. (1986) used 0.17moll-1 ammonium oxalate +0.1 moll- 1 oxalic acid. The extraction is sensitive to light (Mitchell and Mackenzie, 1954) and particularly to ultraviolet light (Endredy, 1963). Schwertmann (1964) showed that in the dark the amorphous iron oxides were mainly attacked and under ultraviolet illumination the crystalline phases were dissolved as effectively as by the dithionite reagent. Heavy metals are released, with the exception of lead and cadmium whose oxalates are poorly soluble and which coprecipitate with calcium oxalate. The use of oxalic... 

Temperature influences the structure of TiC>2 synthesized as a nanolayer on SiC>2 and AI2O3. After 12 cycles at temperatures below 350°C on SiC>2, only anatase is formed. Above 600°C predominantly rutile is formed. At intermediate temperatures a mix of the two phases is formed. On aluminium oxide however, at low temperature the biphase system is formed. At 600°C 100%, anatase is formed on AI2O3. This illustrates the effect of the mutual influence of the matrix surface and the nanolayer on phase transformations in core-shell system. 

Aluminium and Precipitator Ash. In some Victorian brown coals significant quantities of acid-soluble aluminium are found. This is believed to be present as aluminium hydroxide which is dispersed throughout the water phase of the coal. During combustion of this coal, the refractory aluminium oxide formed takes the shape of the relics of the plant material present in the coal, thus forming an extremely low density ash (approximately 100 kg/m ). Whilst the collection of these particles by electrostatic precipitation is possible, the problem of reentrainment on rapping has necessitated the use of larger sized units than would otherwise be required. It is therefore important to determine the acid soluble aluminium fraction in the coal to determine if precipitation of fly ash is likely to be a problem. 

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