Particulates fused silica

Grade 2 water to reverse osmosis or de-ionisation, followed by filtration through a membrane filter of pore size 0.2 jum to remove particulate matter. Alternatively, Grade 2 water may be redistilled in an apparatus constructed from fused silica. 

These have now been superseded by capillary columns, which offer greatly improved separation efficiency.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. 

In other cases, stationary phases have been tailored to achieve specific separations. In one case, a new stationary phase was designed to achieve the separation of a particular mixture of volatile priority water pollutants whose separation has posed a real problem (6, 7). A serendipitous finding was that this new stationary phase, DB-1301, also promises to be very useful for the separation of some chlorinated pesticides. Nor have we reached the end of this road an Immobilized form of 2330, with utility for those Interested In dioxins, In positional Isomers of the fatty acids, and In other challenging separations, will soon be available. Fused silica columns with bonded particulate materials, reminiscent of the old PLOT-type columns, are also available. The primary utility of the PLOT-type columns currently available Is for fixed gas analysis, but newer types on the horizon will permit a choice of adsorptive-type separations, partition-type separations, or a combination of both. 

CEC columns are generally made of fused-silica tubing, usually packed with the appropriate stationary phase. Today, the most commonly used CEC columns have i.d. of 100 p,m or less, with 50 and 75 p,m i.d. being the most popular. The stationary phase is retained in the column by two frits. Column designs can be categorized into two major types OT columns and packed structures, which include packed columns, monolithic columns, and microfabricated stractures (open or continuous beds). Packed capillary columns are most commonly used, as has been demonstrated in numerous papers [9-11]. They can be subdivided into three different categories columns packed with particles, columns with continuous beds fabricated in situ creating a rod-like monolithic structure, and columns with immobilized or entrapped particulate materials. 

SEM microphotogaphs and EDAX scans of the cross section and outer surface of the slag deposit, illustrated in Figure 10, indicate the chemistry of the deposit is not uniform. The bulk of the fused material is rich in silica, low in iron, and virtually depleted of potassium. The outermost layers, no more than 2 to 3p thick, are very rich in iron and frequently also rich in calcium. On occasion, the outer surface is covered with small particulate, several microns in diameter, or undissolved cubic or octahedral crystals whose origin is pyrites. Similar formations have been observed in full-scale operation. The evidence indicates deposits form under axial symmetric flow conditions in the furnace by the fluxing action at the heat transfer surface of small particles, <8p in diameter, of decidedly different chemical composition and mineral source. Migration of the fly ash to the surface is by means of eddy diffusion, thermophoresis, or Brownian motion. 

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