Dissolution measurement

Purpose of analytical procedure Characteristics Identification Testing for impurities Quantitat. Limit Assay - dissolution (measurement only) - content/potency... 

Dissolution Measurement. Resist solutions 1n mixtures of Isoamyl acetate/cyclohexanone/methyl Isobutyl ketone (90 5 5 by volume) were filtered through 0.45 pm disc filters, then spin-coated onto silicon wafers at about 2000 rpm. The coated wafers were prebaked 1n a convection oven at 90°C for 1 hour, then stored 1n a desiccator. The basicities of the alkaline solutions were titrated by a standard HC1 solution with a Fisher Accument pH meter, Model 805 MP. The film thickness 1s about 2 pm. Resist dissolution was measured by a He-Ne laser Interferometer 1n a thermostated bath at the desired temperatures (12.131-... 

The dissolution measurements of the two products (test and reference, pre- and post-change, two strengths) should be made under the same test conditions. The dissolution time points for both the profiles should be the same, e.g., for IR products 15, 30, 45, and 60 min, for extended-release products 1, 2, 3, 5, and 8 hr. 

Type of Analytical Procedure Characteristics Identification Testing for Impurities Assay - Dissolution (Measurement Only) - Content/ Potency... 

Dissolution measurements under the microscope give several results which will be discussed separately. The first and most evident result is the penetration velocity of the solvent into the polymer. In order to judge the influence of the solvent s chemical constitution on the polymer we have chosen a number of phthalic acid esters which differ only in their ester groups and which are well known plasticizers. The polymer was a vinyl chloride-vinyl acetate (87 13) copolymer. The following plasticizers have been tested, (the abbreviations are indicated)... 

We aimed to draw more conclusions from these dissolution measurements also by measuring the thermodynamic properties. This was done quantitatively by... 

Although chemical constitution obviously plays the major role in determining the thermodynamic quality of a solvent, the influence of steric properties on solvent quality remains an open question. In order to answer this question we have plotted our dissolution-measurement-indicator for thermodynamic quality—the gel fraction molecular weight which stands for the size of the molecule (Figure... 

Dissolution measurements under the microscope, therefore, are a powerful tool for selecting solvents or plasticizers. Measurements of elastic range extension give insight into structural changes caused by plasticizers. Thermal diffusivity and heat conductivity measurements are recommended to detect side group and other transitions in polymers and other substances. 

The silicon-rubber-based graphite electrode has been employed as an appropriate voltammetric sensor to measure the rates of dissolution of several oxidizable pharmaceutical compounds [169]. The recirculating dissolution measuring arrangement with this sensing electrode and an Ag/AgCl reference are... 

From such microbubble-dissolution measurements, Bemd (ref. 16,17) outlined a physical model to explain much of the dynamic behavior of film-stabilized microbubbles.- One problematic aspect of this dynamic behavior involved the question of how a gas nucleus can be surrounded by a relatively impermeable film and yet subsequently act to produce cavitation when a gas/water interface is needed to initiate cavitation. Bernd (ref. 16) explains that if the stabilized gas microbubble enters a low-pressure area, the gas within the microbubble will attempt to expand. The surfactant film may also elastically attempt to expand. The surfactant film will then be expanded until essentially the surface tension of the water alone acts to contract the microbubble, since the protective shell no longer acts. The film has either been ruptured upon expansion, or it has expanded until it is ineffectual. Thus the microbubble (i.e., gas nucleus) should be capable of expanding to form a cavitation void or acquire additional gas in the form of water vapor or from surrounding dissolved gas. In addition, Bernd points out that it is reasonable to expect a gas microbubble to acquire such an effective... 

Both Peterson (41) and Berger (42) found that dissolution started at approximately 0.5 km water depth and the rate of dissolution increased slowly with increasing water depth until a depth of approximately 3.8 km was reached. Below this depth the rate of dissolution rapidly increased with increasing water depth. The change in the saturation state of seawater, with respect to calcite, in the deep water of this region is close to linear with depth (43). Consequently, the results of these experiments indicated that the rate of dissolution was not simply related to saturation state. Edmond (44) proposed that the rapid increase in dissolution rate could be attributed to a change in water velocity. Morse and Berner (45) pointed out that this could be true only if the rate of dissolution was transport controlled. Their calculations indicated that the rate of dissolution measured by Peterson (41) was over 20 times too slow for diffusion controlled dissolution, this being the slowest transport process. 

A major problem encountered in comparing the rates of dissolution measured in the laboratory with rates measured in the water column was that the rates measured in the laboratory were 10 to 100 times faster. It has subsequently been shown (30) that the difference in rates for the biogenic calcite can be largely attributed to the fact that Berger (42) used only large foramin-ifera, while Morse and Berner (45) used a total carbonate sediment sample. The reason for the difference in rates for the Iceland spar and synthetic calcites is less certain. One possibility is that surfaces exposed in seawater experience biofouling. 

Table VL Viscosity Values for Solutions Containing 2-14% Cellulose in TFA-CH2Q2 (70 30 v/v) After 12 Days of Dissolution. Measurements Were Made at 2S°C with a Wells-Brookfield Mode HBT Cone(Plate VisoMneter...

Indicates dissolution measured for less than 1000 h. Indicates normalized by initial surface area. Indicates normalized by final surface area. 

Biopharmaceutic studies (in vitro) Drug release/dissolution Measurement of the rate of drug dissolved under specified conditions... 

It is clear from the DTA curves that Form I is the more stable polymorph in the high-temperature range. However, based upon solubility and rate of dissolution measurements (Tables 3-2 and 3-3 and Fig. 3-4), the reverse situation applies at lower temperatures. Form II is more stable near room temperature. The extrapolation of the solubility and dissolution rate date indicate a transition point at about 165°C for Form II to Form I. This transition is not observed in the DTA curve for Form II, as it should be if the situation were thermodynamically ideal. The lack of transition in the DTA curve corresponds to a case of suspended transformation. Forms I and II of sulindac are enantiotropic polymorphs, with Form II being more stable at room temperature (McCauley 1991). 

Type of analytical procedure characteristics Identification Testing for impurities Quantitation Limit Assay dissolution (measurement only) content/ potency... 

Dissolution measurements in the absence of supporting electrolyte were made on both electrochemically grown films and pressed pellets of AgCl, with similar results (7). Approach curves for tips characterized by a = 5, 12.5, and 25 /xm, constructed by plotting the normalized long-time currents, from chronoamperometric measurements, as a function of normalized tip-substrate distance are shown in Figure 34a and b. The curves cover different values of L since, in each case, measurements were made over a range of distances up to 2 /xm from the substrate surface. For comparison with the experimental data, theoretical approach curves are also shown for second-... 

K. Tachibana and M.B. Ives, Selective Dissolution Measurements to Determine the Nature of Films on Nickel-Molybdenum Alloys, Passivity of Metals, The Electrochemical Society, 1978, p 878-897... 

Figure 2. Thrombus growth and dissolution measured by carotid artery catheter region-of-interest scintillation counting.

Dissolution processes. We used X-ray reflectivity measurements to probe the changes in orthoclase surface structure and termination in real time during dissolution. Measurements of the dissolution process were performed in situ in flowing solutions of 0.1 M HC1 and 0.1 M NaOH, having pH values (at 25 °C) of 1.1 and 12.9, respectively (Teng et al. 2001). 

One area of concern associated with intrinsic dissolution measurements is associated with the preparation of the solid disc by compaction of the drug particles. If a phase transformation is induced by compression, one might unintentionally measure the dissolution rate of a polymorph different from the intended one. This situation was encountered with phenylbutazone, where Form III was transformed to the most stable modification (Form IV) during the initial compression step [90]. 

Dissolution Measurements. Dissolution rate measurements of the benzophenone series were made on a Perkin-Elmer Dissolution Rate Monitor (DRM-5900) in puddle development mode with 0.25 N KOH developer. The DRM was computer-controlled using Perkin Elmer DRM analytical software (DREAMS 3.0). Measurements of the sulfonyl/carbonyl esters were made with 0.26 N tetramethyl-ammonium hydroxide (TMAH). Reported dissolution rates DRj/i) are at half film thickness. 

Characteristic Identification Quantitative Limits Dissolution measurement only Content/potency... 

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