Solubility rate measurements

Solubility Rate Measurements. Solubility rates, Sr, were determined by measuring PBS film thickness as a function of development time. PBS films coated on silicon wafers were broken into several pieces. Each piece was dipped into n-butyl acetate, BuAc, and the development time measured. The film was rinsed in isopropanol and baked at 120 C for 30 minutes to remove residual solvents. Film thickness was measured by interferometry. The temperature of the developer, BuAc, was controlled at 2S C O.OS C and the developer was not stirred or agitated during the deydopment process. Plot of film thickness vs. development time were linear for low Mw films. Films having M, greater than 400,000 g/mole did not completely dissolve in BuAc. 

In an extension of this work, pellets of a blend of PCL and hy-droxypropylcellulose containing fluridone were prepared by grinding, blending, and then melt-spinning the mixture with a Berstorff twin screw extruder (78). The extruded rod was subsequently water-quenched and pelletized. Pellets were also prepared by coating bundles of extruded rods with the water-soluble excipients PEG 3350 and PEG 600 (95 5). In vitro release rate measurements were conducted in the simulant medium of 50% aqueous ethanol or hardened water. 

Certain surface-active compounds [499], when dissolved in water under conditions of saturation, form self-associated aggregates [39,486-488] or micelles [39,485], which can interfere with the determination of the true aqueous solubility and the pKa of the compound. When the compounds are very sparingly soluble in water, additives can be used to enhance the rate of dissolution [494,495], One can consider DMSO used in this sense. However, the presence of these solvents can in some cases interfere with the determination of the true aqueous solubility. If measurements are done in the presence of simple surfactants [500], bile salts [501], complexing agents such as cyclodextrins [489 191,493], or ion-pair-forming counterions [492], extensive considerations need to be applied in attempting to extract the true aqueous solubility from the data. Such corrective measures are described below. 

C Nystrom, J Mazur, MI Barnett, M Glazer. Dissolution rate measurements of sparingly soluble compounds with the Coulter counter model TAIL J Pharm Pharmacol 37 217-221, 1985. 

More evidence for enhanced porosity in irradiated PBS films is provided by postexposure annealing experiments. The solubility rate of an irradiated MP20 film which was annealed for 30 minutes at 120 C before dissolution was lower than the solubility rate of the unannealed film. Table IV shows the measured solubility rate loss and the expected solubility rate loss, Sr(IF) — Sr(IP), if all the porosity created during irradiation were removed by annealing. The soluMity rate of the annealed IF-type films are somewhat higher than IP-films of similar M . Thus, the annealing process removes most but not all of the porosity created during irradiation. 

Sol-Gel Measurements. The relative rates of crosslinking and scission may be estimated from soluble-fraction measurements. For an initial random molecular weight distribution and random chain scission, extrapolating a curve of S + S vs. 1/D, where S = sol fraction and D —... 

Another measure of sensitivity can be obtained from the rate of dissolution of exposed versus unexposed film at various doses. The amount of energy needed to obtain some arbitrary ratio of rates or the exponent of the dissolution rate ratio versus dose at high doses may be used. In the present study, both a contrast curve and a solubility rate ratio versus dose data are reported for the copolymer of maleic anhydride with alphamethylstyrene. However, these tests are burdensome when many materials are to be screened... 

Measures of change Viscosity measurements Intrinsic viscosity Viscosity-average molecular weight Molecular weight distribution, GPC Solubility Rates Thickness changes on development... 

The higher sensitivity indicated by the increased GCr) value can also be tested by measuring the solubility rate ratio, S/S0 where... 

For the solubility rate studies, thin films of polymer were spun on silicon wafers as described previously for the G(s) measurement. The wafers were then immersed in the developing solvent at a controlled temperature. The dissolution rate was monitored with a laser-interferometer device (28). In order to compare the dissolution rate ratios of PMMA and p(MMA-MA) (Figure 5) it is important to compare polymers of the same initial molecular weights. The... 

The dissolution rate is directly proportional to the equilibrium solubility if the appropriate experimental conditions such as the ones used for intrinsic dissolution rate measurements are selected. The rotating-disk method is the most useful and most widely used technique for measuring intrinsic dissolution rates. The theoretical considerations and experimental details of this method will be considered later in this chapter in the discussion dealing with dissolution. 

Rate Measures for Interfacial Processes Terminology used for reporting rate data can be confusing. Normally rate data are reported on a volumetric basis with transfer rate and effective area combined. For example, kLa denotes mass-transfer data per unit volume. The L subscript means it is referenced to the molar concentration difference between the interface and the bulk liquid. This is commonly used on data involving a sparingly soluble (high relative volatility) component. Note that the lowercase k means the data deal only with the resistance in the liquid phase. 

Chlorides RCeoCI (R = CHj, CH2CI, CHClz, CCIj) and RCtoCI (R = CHClj) undergo ionization in Cp3CH20H-anisole (1 9 v/v) to form RCeo and RC70, respectively, as short-lived intermediates, the nucleophilic trapping of which resulted in substitution products shown in Figure 20. Anisole was used as a cosolvent to ensure sufficient solubility for the rate measurements, while it also acted as a nucleophile. 

The C0CI2/AlEt2Cl/H2 0 catalyst is heterogeneous and rate measurements have not been reported, but, similar to the soluble catalysts, molecular weights increase in proportion to monomer concentration, and are independent of Al/Co ratio over the range 1—10/1 [167]. 

The composition of dew collected from a Teflon surface was compared to summer rainwater concentrations at a site in Warren, Michigan. This comparison showed that natural dew is similar to rainwater with the exception that dew has much higher concentrations of Ca and Cl and much lower acidity. Dry deposition rates of several species were measured to artificially-generated dew and a dry surface. It was found that deposition rates were 2 to 20 times greater to the artificial dew than to the dry surface indicating that the presence of dew enhances both the retention of dry deposited particles and the absorption of water soluble gases. Measurement of the atmospheric concentrations of the depositing species permitted the calculation of deposition velocities for particulate... 

Viscosity measurements used to describe polymer solubility are based on the Brookfield model LVF, at 60 rpm after 1 min spindle revolution. This is a rotational type viscometer which can vary its shear rate by spindle speed changes. Only one-point (shear rate) measurements were made however. This type of reporting puts it on a par with the efflux type viscometers used in the coating industry in that only one shear rate is used. 

The rates measured reflect directly the physical-chemical properties of the water molecule in the nearby hydration shell. These measurements can gauge the properties of the water in an active site where biochemical catalysis takes place. Insertion of proton emitter in a specific site can be useful to determine the internal geometry of a site in a soluble, functioning protein. The subnanosecond measurement is equivalent to a strobe light that freezes in time a transient conformation of a protein. 

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