Additives entrapment

Cumulative volume curves generated by intruding mercury into porous samples are not followed as the pressure is lowered and mercury extrudes out of the pores. In all cases the depressurization curve lies above the pressurization curve and the hysteresis loop does not close even when the pressure is returned to zero, indicating that some mercury is entrapped in the pores. Usually after the sample has been subjected to a first pressurization-depressurization cycle, no additional entrapment occurs during subsequent cycles. In some cases, however, a third or even fourth cycle is required before entrapment ceases. 

The incorporation of drug-loaded liposomes in adequate formulations can improve their stability, allowing their applicability in vaginal drug delivery [151], Additionally, entrapment of drugs in liposomes may improve their solubility and... 

Many types of gloves are manufactured for different purposes. Proper selection of gloves is important to ensure that the solvent, or other chemical compound, cannot penetrate through the glove, where its subsequent evaporation would be prevented by the glove itself Exposure to the additive entrapped between the glove and the skin is more severe than the exposure to the additive without the glove. 

Direct Compression. This process is relatively simple and time saving. AH the ingredients are blended and then compressed into the final tablet. This is an excellent method, but encumbered by a number of problems. Not all substances can be compressed directly, necessitating a granulation step. Likewise, the flow properties of many blends of fine, particle-sized powders are not such as to ensure even filling of the die cavities of tablet presses. In addition, air entrapment can occur. 

Coagulation involves neutralizing charged particles to destabilize suspended soflds. In most clarification processes, a flocculation step then follows. Flocculation starts when neutralized or entrapped particles begin to colUde and fuse to form larger particles. This process can occur naturally or can be enhanced by the addition of polymeric flocculant aids. 

In all metal spraying processes the particles emerge from the nozzle in a conical stream, and although the particles near the centre are molten, those at the periphery have solidified. In the powder process there are in addition solid particles which have not melted. The solid particles tend to become entrapped in the coating, making it porous. The effect is more pronounced in the powder process owing to the larger number of solid particles present. 

Cationic quaternary ammonium compounds such as distearyldimethylammonium-chloride (DSDMAC) used as a softener and as an antistatic, form hydrated particles in a dispersed phase having a similar structure to that of the multilayered liposomes or vesicles of phospholipids 77,79). This liposome-like structure could be made visible by electron microscopy using the freeze-fracture replica technique as shown by Okumura et al. 79). The concentric circles observed should be bimolecular lamellar layers with the sandwiched parts being the entrapped water. In addition, the longest spacings of the small angle X-ray diffraction pattern can be attributed to the inter-lamellar distances. These liposome structures are formed by the hydrated detergent not only in the gel state but also at relatively low concentrations. 

Nonfills Air entrapment Gel and/or resin timet too short Additional air vents and/or vacuum required Adjust resin mix to lengthen time cycle... 

Networks obtained by anionic end-linking processes are not necessarily free of defects 106). There are always some dangling chains — which do not contribute to the elasticity of the network — and the formation of loops and of double connections cannot be excluded either. The probability of occurrence, of such defects decreases as the concentration of the reaction medium increases. Conversely, when the concentration is very high the network may contain entrapped entanglements which act as additional crosslinks. It remains that, upon reaction, the linear precursor chains (which are characterized independently) become elastically effective network chains, even though their number may be slightly lower than expected because of the defects. 

The presence of redox catalysts in the electrode coatings is not essential in the c s cited alx)ve because the entrapped redox species are of sufficient quantity to provide redox conductivity. However, the presence of an additional redox catalyst may be useful to support redox conductivity or when specific chemical redox catalysis is used. An excellent example of the latter is an analytical electrode for the low level detection of alkylating agents using a vitamin 8,2 epoxy polymer on basal plane pyrolytic graphite The preconcentration step involves irreversible oxidative addition of R-X to the Co complex (see Scheme 8, Sect. 4.4). The detection by reductive voltammetry, in a two electron step, releases R that can be protonated in the medium. Simultaneously the original Co complex is restored and the electrode can be re-used. Reproducible relations between preconcentration times as well as R-X concentrations in the test solutions and voltammetric peak currents were established. The detection limit for methyl iodide is in the submicromolar range. 

In its more recent phase of development, the multidisciplinary nature of metal-vapor cryochemistry is becoming evident with, for example, chemical physicists attempting to explain subtle, spectroscopic phenomena associated with matrix-entrapped, metal atomic species (75-77). A clear display of renewed physics interest in the field may be seen from a glance at the proceedings of the International Conference of Matrix Isolation Spectroscopy (Ber. Bunsenges. Phys. Chem., January, 1978). In addition, matrix reactions are providing unique, syn-... 

Phase separation microencapsulation procedures are suitable for entrapping water-soluble agents in lactide/glycolide excipients. Generally, the phase separation process involves coacervation of the polymer from an organic solvent by addition of a nonsolvent such as silicone oil. This process has proven useful for microencapsulation of water-soluble peptides and macromolecules (48). 

FIGURE 8 Antitumor activity of free DXR and DXR entrapped in different liposome types in solid IgM immunocytoraa-bearing Lou/M Wsl rats. 2 mg DXR/kg body weight was injected i.v. daily for 5 days (0-4) followed by one additional injection at day 11 after start of therapy. Results obtained during the first 21 days after start of treatment are shown. Treatment groups consisted of 10 animals. 

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