Dessicant, silica

Anhydrous An anhydrous material does not contain any water molecules. Many substances occur naturally as hydrates, compounds that have a specific number of water molecules attached to them. This water can often be removed by heating and/or vacuum to give the anhydrous material. Anhydrous materials can absorb water from their surroundings and find use as dessicants. Examples include those packets of silica gel you find in some consumer goods, as well as dehumidifying sachets used in clothes closets. When an anhydrous material reacts with water, this could release a large amount of heat, possibly leading to a heat or pressure buildup that could result in an explosion. 

In fact, it is extremely important to eliminate as completely as possible the solvent imbedded into the thin layer of coated adsorbent. It is achieved conveniently first by air-drying the TLC plates for a duration of 30 minutes and then in a hot-air oven maintained at 110 °C for another 30 minutes and subsequently cooling them in a dessicator. This drying process helps a great extent in rendering the adsorbent layer active. In order to achieve very active layers, silica gel and alumina coated plates may be heated upto 150 °C for a duration of 4 hours and colling them in a dessicator. 

Table 2. Structural characteristics of initial fumed silica A-200 and hybrid pyrocarbon/silica adsorbents prepared by mechanical mixing of oxide with starch (St) or cellulose (C), saturation with water vapour in dessicator for 48 hours and subsequent carbonization.5...

Silica-gel thin-layer chromatography plates (Fisher catalog 05-713-317)—Heat at 100°C for 10 min just before use. (Store dessicated at room temperature.) Twenty-five will be required we try to fit two groups on one plate. 

Fig. 6. Adsorption capacity of various dessicants vs years of service in dehydrating high pressure natural gas (39). a, Alumina H-151, gas r- 27°C and 123 kPa, from oil and water separators b, silica gel, gas 38° C and 145 kPa, from oil absorption plant c, sorbead, 136-kPa gas from absorption plant ...

In general, basic compounds are retained more strongly on mildly acidic surfaces, such as silica or acidic alumina. Acidic compounds are retained on basic surfaces, such as basic alumina. Because both silica and alumina are hydroscopic, they adsorb water to their surface. This water greatly reduces the retention of organic solutes because it deactivates the hydrogen-bonding sites. Thus, it is important to keep the SPE sorbents dry and free from water. They may be stored in a dessicator prior to use. Very polar compounds, such as carbohydrates or amino compounds, are tightly bound to nonbonded normal-phase sorbents, such as silica and alumina. However, the use of cyanopropyl or aminopropyl phases often permit the recovery of these compounds when silica does not work. 

The CRM consists of 0.317 g artificially contaminated spray dried milk contained in an ochre/white gelatin capsule. The strain used for the contamination is Bacillus cereus (ATCC 9139). The capsules are packed in a plastic container with a silica gel dessicant bag. 

The product was dried in a vacuum dessicator over silica gel to constant weight. After optimisation of sulfonation conditions, all graft copolymers for ion exchange experiments were sulfonated at 90 for 45 minutes. 

CT - chemical traps 120-150 mL of Silica Gel 60 (230/ ifOO mesh, EM Reagents, methanol-rinsed, activated at 110, 20 hours) in high pressure traps (prototypes, Adsorbents and Dessicants of America)... 

To show the variety of isotherm shapes for a single adsorbate, data for water adsorbed from air on three dessicants are given in Fig. 25.3. Silica gel has a nearly... 

Normal phase plates (silica, alumina) should be stored in a dessicator, as they are prone to pick up water from the atmosphere and become deactivated (lose their ability to resolve compounds). In some cases, plates may be activated by drying in an oven before use. 

Activate the silica gel coated plates by heating in a ventilated oven for 30 min at 110°C. Store the plates in a dessicator until use, they should be used on the same day that they are activated. 

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