Storage, gels

For longer term storage, gels may be stored wet at 4°C. The wet gel should be wrapped in a piece of plastic wrap. This permits handling the gel without risk of breakage. The wrapped gel can be stored in a sealable bag for <1 year at 4°C. To preserve gels indefinitely, they may be either vacuum dried onto filter paper or air dried between sheets of cellophane. 

Certain grades of siUca gel or selected clay minerals are often used. The buffeting material is preconditioned under the selected relative humidity and, after equihbration, installed in the case. This method of microclimate control has proven to be very efficient, not only in exhibition cases and storage spaces, but also in packing crates used for the transportation of sensitive objects. 

Properties. CoUoidal siUca is a stable aqueous dispersion or sol of discrete amorphous siUca particles having diameters of 1 to 100 nm. SiUca sols do not gel or setde out of solution for at least several years of storage. Aqueous sols that contain up to 50% siUca have been developed (30,31). Particle sizes of approximately 130 nm in diameter are possible (32), but slowly settle out of solution. 

ProStep, developed by Elan and marketed by Ledede, dehvers nicotine over 24 hours (107) and is available ia a 22 mg dose (108). The system consists of a nicotine-containing carrageenan gel embedded and heat-sealed iato a foil—polyethylene laminate to isolate the nicotine from a peripheral acryhc adhesive duriag storage. 

Dehydration of TSK-GEL columns can result from improper use or during long-term storage. This condition can be remedied by the following procedure. 

The gel is supplied as a suspension in 20% aqueous ethanol. Before packing the storage solution should be removed from the gel. 

Transfer excess gel from the filling tube into a bottle supplied with storage medium. 

X. COLUMN AND GEL MAINTENANCE. CLEANING, REGENERATION, AND STORAGE METHODS... 

F rom 5-deoxy-5-iodo-1,2-0-isopropylidene-/ -l-arabinofura-nose (37). Anhydrous silver fluoride (600 mg.) was added to a solution of 300 mg. of 37 in pyridine (4.0 ml.), and the mixture was shaken at room temperature for 24 hours. Ether (4 ml.) was added, and the mixture was passed through a column of silica gel (1.5 X 12 cm.). The column was washed with ether/pyridine, 1 1 v/v. (10 ml.), and the effluent, which contained 5-deoxy-l,2-0-isopropylidene-/ -L-threo-pent-4-enofuranose (33), was concentrated to 4 ml. Acetic anhydride (0.2 ml.) was added, and the reaction mixture was kept at room temperature for 16 hours. Concentration afforded a sirup from which the last traces of solvent were removed by storage in high vacuum at 20°C. The sirup was distilled at 90°C. (bath) at 2.5 X HHmm. The distillate (110 mg., 51%), which crystallized on standing, had physical constants which were identical to material prepared as above. 

Yield of the crude product according to the NMR spectra. In parentheses yield of the isolated pure hydrazine. Hydrazines arc known to be prone to air oxidation and unstable upon storage or handling on silica gel. This might be the reason for the considerable loss of yield during purification. 

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