Residual solvent concerns

Alternatives to compounding in the melt are solution mixing or powder blending of solid particles. Mixing with the aid of solvents can be performed at lower temperatures with minimal shear. However, difficulties in removal of the solvent results in plasticization of tJie polymer matrix and altered erosion/drug release performance in addition to residual solvent toxicity concerns. Powder blending at room temperature minimizes thermal/shear stresses, but achieving intimate mixtures is difficult. 

For difficult separations, multiple extractions are frequently carried out, although in many cases the background is also coextracted. Using multiple extractions, polar interferences may sometimes be transferred from the aqueous into organic solvents that can dissolve minute amounts of water. This problem cannot be eliminated by simple presaturation of the extraction solvent but only by washing the extract with small amounts of water (58). Another relevant issue to be considered in trace residue analysis concerns the purity of the organic solvents, since they can introduce solvent impurities into the sample extract. Therefore, the need for high solvent purification should not be overlooked in some applications. 

Organic coating was the first choice in earlier times. Film formation takes place when the solvent evaporates. However, because of increasing environmental concerns and increasing regulatory restrictions of residual solvent content in the final formulation, coating material suppliers have been highly motivated to develop aqueous systems. 

As well as predicting protein structure, it is also of interest to try to predict solvent accessibility from the protein s primary sequence of amino acid residues. Solvent accessibility concerns the area of a protein s surface that is exposed to the surrounding solvent. The importance of this concept is that these accessible regions have the potential to interact with other entities, including endogenous proteins and drugs. Similarly, if the protein of interest is an enzyme, only residues with solvent accessibility could be part of the enzyme s active site. This means that an interaction site of interest, one involved in signal transduction (see Krauss, 2003), requires spatial accessibility to the solvent (Ofiran and Rost, 2005). 

The most important extraction technique nowadays is simple solvent extraction. The traditional solvent for extraction was benzene, but this has been superseded by other solvents because of concern over the possible toxic effects of benzene on those working with it. Petroleum ether, acetone, hexane and ethyl acetate, together with various combinations of these, are typical solvents used for extraction. Recently, there has been a great deal of interest in the use of carbon dioxide as an extraction solvent. The process is normally referred to as super-critical carbon dioxide extraction but, in fact, the pressures employed are usually below the critical pressure and the extraction medium is sub-critical, liquid carbon dioxide. The pressure required to liquefy carbon dioxide at ambient temperature is still considerable and thus the necessary equipment is expensive. This is reflected in the cost of the oils produced, but carbon dioxide has the advantage that it is easily removed and there are no concerns about residual solvent levels. 

The invention concerns the use of supercritical solvents to extract the cocoa butter from cocoa nibs (comminuted cocoa beans) and cocoa mass (fmely crushed beans). The description of other processes in the prior art section of the patent points out that organic solvent extraction results in the presence of residual solvents. Additionally, some of the newer pressing methods, via expellors, for example, introduce waste bean contaminants into the butter which must be removed with economic and taste penalties. 

In the construction industry, residual solvent evaporation becomes an increasingly more critical issue, especially in the case of products used for indoor applications. Sealants, adhesives, and paints are now a major focus of this concern since they contribute to indoor pollution. Similar trends are observed in the automotive industry where both solvents and plasticizers are suspected of contributing to a plastics odor in car interiors. 

Figure 16.2.3. Typical chromatogram of class 1 solvents using the conditions described for system A and procedure 1. Flame-ionization detector. 4 benzene 10 carbon tetrachloride 14 1,2-dichloroethane 15 1,1-dichloroethylene 52 1,1,1-trichloroethane. [Adapted, by permission, horn European Pharmacopoeia, Addendum 2000, pp31-36.] [Please note that iirformation concerning residual solvents are susceptible to be modified...

---