Solubility classes

Gra.nula.r Compositions. Granular compositions of UF reaction products are divided into three classes, each based on their degree of water solubihty as affected by their polymer distributions, ie, ureaform, the least water-soluble class methylene ureas and methylene diurea/dimethylene triurea (MDU/DMTU) compositions, the shortest-chain MU oligomers and the most water-soluble. 

Biopharmaceutics Classification System Redefining BSC Solubility Class Boundary... 

A special case in dissolution-limited bioavailability occurs when the assumption of sink condition in vivo fails that is, the drug concentration in the intestine is dose to the saturation solubility. Class IV compounds, according to BCS, are most prone to this situation due to the combination of low solubility and low permeability, although the same could also happen for class II compounds, depending primarily on the ratio between dose and solubility. Non-sink conditions in vivo lead to less than proportional increases of bioavailability for increased doses. This is illustrated in Fig. 21.8, where the fraction of drug absorbed has been simulated by use of an compartmental absorption and intestinal transit model [35] for different doses and for different permeabilities of a low-solubility, aprotic compound. 

Doses to sections of the GI tract were calculated according to the model presented in ICRP (1959). The critical organ for each of these nuclides is indicated in Table 25 for each solubility class and for the two modes of exposure considered in that publication. 

Many investigations of relationships between composition and properties take into account only the concentration of the asphaltene constituents, independent of quality criterion. However, a distinction should be made between the asphaltene constituents that occur in straight-run resids and those that occur in blown asphalts. Remembering that asphaltene constituents are a solubility class rather than a distinct chemical class means that vast differences occur in the makeup of this fraction when it is produced by different processes. 

Assumed Solubility Class Intake Mode Bone ash, (ng/g) ... 

DF Houston, T Iawasaki, A Mohammad, L Chen. Radial distribution of protein by solubility classes in the milled rice kernel. J Agric Food Chem 16 720-724, 1968. 

Fractionation of petroleum in the refinery, to obtain streams with specific boiling ranges for various downstream processes, is performed by distillation in a crude unit. To determine how Ni and V compounds are distributed as a function of boiling point is, therefore, useful for evaluating their impact in the refinery. Petroleum may also be fractionated by solvent separation and chromatography to obtain more detailed information on the distribution of Ni and V compounds. This section will review the available literature on how metals are distributed in petroleum by boiling point and solubility class. It will also include some discussion of the structure of heavy oil in general and asphaltenes in particular. Vercier etal. (1981) have provided an excellent review of methods and procedures involved in petroleum fractionations. 

Metal Porphyrin and Nonporphyrin Distribution in Petroleum Solubility Classes... 

Asphaltenes are thought to be the most complex, high-molecular-weight, high-boiling components in petroleum. Asphaltenes constitute a solubility class of materials consisting primarily of highly polar and... 

Although the residuum is a mixture too complex for isolating chemically pure components, asphaltene investigators in recent years have developed techniques that separate residuum molecules on the basis of compound class rather than solubility class. These studies, discussed next, have greatly modified the concepts of asphaltene structure. 

With regard to the heterogeneity or homogeneity of these systems one may make the following generalizations 1. The alkali metal initiated polymerizations are heterogeneous, at least with respect to initiation, by virtue of the insolubility of the alkali metals in the various solvents. 2. In polar solvents the alkyl alkali metal systems appear to represent a soluble class of initiator systems. 

Class I high permeability, high solubility Class II high permeability, low solubility Class III low permeability, high solubility Class IV low permeability, low solubility... 

Asphaltenes are, by definition, a solubility class (8, 9, 10) that is precipitated from petroleums and bitumens by the addition of a minimum of forty volumes of the liquid hydrocarbon. In spite of this, there are still reports of asphaltenes being isolated from crude oil by much lower proportions of the precipitating medium (II), which leads to errors not only in the determination of the amount of asphaltenes in the crude oil but also in the determination of the compound type. For example, when insufficient proportions of the precipitating medium are used, resins (a fraction isolated at a later stage of the separation procedure by adsorbtion chromatography) also may appear within the asphaltene fraction by adsorbtion onto the asphaltenes from the supernatant liquid and can be released by reprecipitation in the correct manner (12). Thus, questionable isolation techniques throw serious doubt on any conclusions drawn from subsequent work done on the isolated material. 

For the control of internal doses, annual limits of intake (ALI) and derived air concentrations (DAC) have been determined. ALIs and DACs in EPA guidance and the USNRC and DOE regulations are based on the recommendations of the ICRP (ICRP 1979). Values of the ALIs and DACs for uranium isotopes are presented in Table 7-1. These values are for soluble. Class D (Days) material, which has a half-time for clearance from the pulmonary region of the lung of less than 10 days. Values of ALIs and DACs for Class W (Weeks) and Class Y (Years) uranium are available in Appendix B to 10 CFR 20 (USNRC 1993f). 

Where several e(50) values are given depending upon the solubility class of the radionuclide and the speed of metabolism in the body, the bounding or highest value in any solubility class is used. For some radionuclides and a few waste streams, it is possible that following loss of control, inhalation could provide a significant exposure pathway relative to the ingestion accounted for in the SITP. This would be a waste stream that is in the form of a gas, fine particulates or an unstable material (e.g. sodium) which could convert from a solid to fine particulate. 

An intermediate solubility class should be introduced given the tendency of many acids and bases to be highly soluble at pH 6.8 and 1.2, respectively. 

A comparison of the DCS value estimated using in silica, HTS and rat in situ perfusion estimated for a given subset of clinical candidates is given in Table 1 based on internal historical data. As indicated, in silica data predicted DCS class correctly in 74% of cases and HTS data in 81% of cases using rat in situ perfusion as the reference data set. In many cases, errors were associated with the misclassification of DCS Class I or III with class II or IV (permeability errors). Misclassifications based on solubility errors were less common. Also some very poorly soluble Class II compounds can masquerade as Class IV candidates based on precipitation and adsorption to the hlters and plastics associated with the permeability apparatus. 

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