Dissolution microparticles

Diebold SM, Dressman JB. Dissolution of microparticles—a hydrodynamically based contribution to an unresolved pharmaceutical issue. Pharm Res. In preparation. 

A number of electrochemical processes involving solid materials can be described in terms of the reductive or oxidative dissolution of such materials. Within this type of processes, one can include the stripping of metal deposits previously mentioned. In the context of archaeometry, conservation, and restoration sciences, the reductive dissolution of iron oxide-type materials is of particular interest. Thus, application of the voltammetry of the microparticles approach for identifying iron pigments has been described [108, 137-139]. 

Grygar T (1998) Phonomenological kinetics of irreversible electrochemical dissolution of metal-oxide microparticles. J Solid State Electrochem 2 127-136. 

In addition, the enzymic disintegration of the prepared albumin microparticles was systematically evaluated by carrying out a dissolution process in the presence of trypsin. 

Muhrer, G., U. Meier, F. Fusaro, S.AIbano, andM. Mazzotti. 2006. Use of compressed gas precipitation to enhance the dissolution behavior of a poorly water-soluble drug Generation of drug microparticles and drug-polymer solid dispersioriat J Pham308 69-83. 

Some problems associated with conventional LLC (e.g., the loss of the liquid stationary phase through dissolution in the mobile phase) may be obviated by chemically bonding the liquid stationary phase to the support medium. This type of liquid-liquid chromatography is designated bonded phase chromatography (BPC)(11). Since the properties of bonded phases may differ substantially from those of coated phases, BPC separation characteristics may differ from those of conventional LLC. Many phases have exhibited increased efficiency when bonded to the support medium. Most current reverse phase HPLC work involves the use of stationary phases bonded to microparticles. 

A technique based on the formation of a multiple emulsion with an external aqueous phase was developed for the encapsulation of water-soluble drugs in order to replace the external oil phase. Possible unwanted interactions between the oil and the emulsified wax such as swelling or dissolution of the wax, clean-up requirements of the final product, and recovery of the oil phase could be eliminated. In analogy to the encapsulation of water-soluble drugs within polymeric microparticles by a w/o/w-solvent evaporation method, a molten wax phase was used instead of an organic polmer solution. A heated aqueous solution of pseudoephedrine HCl was emulsified into the molten carnauba wax, followed by the emulsification of this w/o-emulsion into a heated external aqueous phase. The temperature of the internal and external aqueous phases had to be kept above the melting temperature of the wax in order to avoid premature... 

Operating pressure and included spherical and needlelike particlesJ Dissolution studies showed the burst release of 22-45% of the drug content followed by an almost complete release over 10 hr. The results indicated that a significant amount of theophylline was on the surface of the microparticles. ... 

Debenedetti and coworkers (88,89) provided one of the first examples of microencapsulation of a drug in the polymeric matrix. Richard and coworkers (90) provided a recent example of the microencapsulation process when they produced microparticles with the encapsulated model protein that showed sustained release. Foster and coworkers (87) also reported precipitation of copper-indomethacin by PVP with a 96-fold enhancement in the dissolution rate of indomethacin. These examples clearly demonstrated the advantages of using supercritical fluid processing for the preparation of polymer-drug formulations with potentially improved therapeutic properties. 

Inorganic pigments and corrosion products of metals have also been studied intensively by using voltammetry of immobilized microparticles. In this way, it was possible to identify hematite as the main corrosion product of a modern steel sculpture in Valencia [64]. Iron (III) oxides and oxide-hydrates are characterized by reductive dissolution signals with very distinct peak potentials and signal shapes. 

Kovanda et al. [67] have employed not only the voltammetry of immobilized microparticles but also several solid-state analytical techniques when studying the thermal behavior of a layered Ni-Mn double hydroxide. The important advantage of these electrochemical experiments was that they proved the presence of substantial amounts of amorphous compounds. Moreover, distinct signals could be identified for the reductive dissolution of the different phases. 

Additional examples of functionalized magnetic materials described in the literature for specific appHcations are summarized in this section. Magnetic microparticles with embedded silicotitanate have shown excellent adsorption ability for radioactive cesium isotope ( Cs) from HEDPA (l-hydroxyethane-l,l-diphosphonic acid), although dissolution of magnetite in acidic solutions in the regeneration step leads to a decrease in magnetic susceptibility (Kaminski and Nunez, 2002). 

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