Effect Of Silica Gel Research Articles

Counting efficiency in the radioassay of 3H- and 14C-labeled lipids adsorbed on silica gel by liquid scintillation

The effect of silica gel on the recovery of radioactivity from 14C- and 3H-labeled lipids by liquid scintillation is analyzed. In the most unfavorable ease, when counting with a toluenefluor solution directly added to the vials containing the adserbed lipid, drastic reductions in the counting efficiency were found, which depended on the amount of silica gel, sample activity, and chemical nature of the lipid. For certain lipids like phosphatidylcholine, these effects were not completely overcome even by introducing water and detergents in the counting system. This paper intends to draw attention to the fact that these factors should be especially taken into account when comparing different lipids from thin-layer chromatograms.

Effect of Silica Gel on Stability and Biological Availability of Ascorbic Acid

The alleged interaction of silica gel and ascorbic acid has been investigated in model experiments and in practical tablet trials, using wet granulation procedures. In simple mixtures stored for 3 weeks at 45° in closed tubes, losses of ascorbic acid increase progressively with increasing moisture content, whether or not silica gel is present, although losses are higher in the presence of silica gel. At an equivalent percentage of water in such mixtures, the amount of silica gel or the prior adsorption of 1 ½ times its weight of vitamin E on the silica gel, did not influence the loss of ascorbic acid. The data show that silica gel binds a certain fraction of the water present and that the loss of ascorbic acid is directly proportional to the amount of unbound water in the system. Sodium ascorbate is more sensitive than ascorbic acid to aerobic oxidation in the presence of moisture. Other commonly used tablet excipients, as well as silica gel, enhance losses of ascorbate. However, proper technology applied to wet granulation procedures yields excellent recoveries and stability of ascorbic acid or sodium ascorbate in dried granulations and in finished multivitamin tablets. The human bioassay technique, in which extra urinary excretion of ascorbic acid after tablet dosage is compared to that after dosage of ascorbic acid in water, has been used to demonstrate the full physiological availability of ascorbic acid in the presence of silica gel. Storage of such tablets for 3 months at 45° did not alter the complete bioavailability of the ascorbic acid.

Effect of silica gel on the technological properties of clays

Effect of silica gel on the technological properties of clays