Wool glass Subject

Figures 4-65, 4-66, and 4-67 show several units of the bag. The bags may be of cotton, wool, synthetic fiber, and glass or asbestos with temperature limits on such use as 180°F, 200°F, 275°F, 650°F respectively, except for unusual rnaterials. (See Table 4-12A and B.) These units are used exclusively on dry solid particles in a gas stream, not being suitable for wet or moist applications. The gases pass through the woven filter cloth, depositing the dust on the surface. At intervals the unit is subject to a de-dust-ing action such as mechanical scraping, shaking or back-flow of clean air or gas to remove the dust from the cloth. The dust settles to the lower section of the unit and is removed. The separation efficiency may be 99%-i-, but is dependent upon the system and nature of the particles. For extremely fine particles a precoat of dry dust similar to that used in some wet filtrations may be required before re-establishing the pi ocess gas-dust flow.

Fig. 7.70 Use Kevlar or glass wool tape on two- and three-fingered clamps, especially if they will be subjected to any heat.

Reactions and distillations carried out in a hood are subject to strong drafts of air and should be protected. In particular distillation apparatus should be carefully wrapped in glass wool or aluminum foil or both, to prevent excessive and uneven cooling. 

Splitless injector liners are normally straight tubes without any flow-disruption devices. Any flow disruption in the injector usually causes peak broadening. Therefore, it is not recommended to pack a splitless liner with glass wool. Sometimes there is a restriction at the bottom of the liner. This is to keep the column centered in the liner and away from the liner walls. Use of small-volume liners will result in greater inlet efficiency, since the sample will be transferred into the column over a shorter period of time. However, smaller-volume liners are more subject to backflash problems. For small injection volumes (<0.5 pi), the 2-mm-I.D. splitless liner is recommended for larger injection volumes, the 4-mm liner is recommended to minimize backflash problems. 

With lipid samples from animal tissues, it is sometimes necessary to purify methyl esters after transesterification has been carried out in order to eliminate cholesterol, which can be troublesome when the esters are subjected to gas chromatography. This can be accomplished by adsorption chromatography with a short column (approx. 2 cm) of silica gel or Florisir in a Pasteur pipette plugged with glass wool, and eluted with hexane-diethyl ether (95 5, v/v 10 mL). The cholesterol and other polar impurities remain on the column. Commercial pre-packed columns (Bond Elut or Sep-Pak ) can be used in a similar way. Methyl esters can also be purified by preparative TLC, with hexane-diethyl ether (9 1, v/v) as the mobile phase. 

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