Dissolution volume

The power input per unit mass of fluid is greater for a dissolution volume of 500 mL than for 900 mL, at a given stirring rate. Remarkably, s calculated for laminar conditions (p = 0.5) employing 500 mL of dissolution medium (not plotted) results in approximately the same hydrodynamic effectiveness as when turbulent conditions are assumed (p = 1.0) for a dissolution volume of 900 mL (10). This implies... 

Fig 6 Correlation between complex dissociation constant, (lOO-lOOOO) dissolution volume (10-1000 ml), and dissolved drug in % (Free + complexed). Hypothetic solubility of the complex 10" mol/l. Black area free dissolved drug, vertically hatched area dissolved complexed drug. 

The corticosteroid dexamethasone has a poor aqueous solubility of 89 microgram/mL. It is given by the oral route for different diseases. When the medicine is given with a glass of water the oral route offers a dissolution volume of about 500 mL in the stomach. When the 4 mg dose used in rheumatic diseases is given by the oral route the dose number will be 0.09 and no major dissolution problems are to be expected. However, when dexamethasone is used in pyodermia gangrenosum the dose has to be 300 mg. At this dose, the dose number will be 6.7. This is close to 10 and the dissolution behaviour of the medicinal product has to be investigated in order to prevent incomplete absorption of the dexamethasone. 

Transfer 1.000 g Hf to Pt dish, add 10 ml of 9 A/ H2SO4, and then slowly add HP drop-wise until dissolution is complete. Dilute to volume with 10% H2SO4. 

Transfer 1.000 g Nb (or 1.4305 g Nb20g) to Pt dish, add 20 ml HP, and heat gently to complete dissolution. Cool, add 40 ml H2SO4, and evaporate to fumes of SO3. Cool and dilute to volume with 8 M H2SO4. 

The performance of the dmg dehvery system needs to be characterized. The rate of dmg release and the total amount of dmg loaded into a dmg dehvery system can be deterrnined in a dissolution apparatus or in a diffusion ceU. Typically, the dmg is released from the dmg dehvery system into a large volume of solvent, such as water or a buffer solution, that is maintained at constant temperature. The receiver solution is weU stirred to provide sink conditions. Samples from the dissolution bath are assayed periodically. The cumulative amount released is then plotted vs time. The release rate is the slope of this curve. The total dmg released is the value of the cumulative amount released that no longer changes with time. 

Acids that are solids can be purified in this way, except that distillation is replaced by repeated crystallisation (preferable from at least two different solvents such as water, alcohol or aqueous alcohol, toluene, toluene/petroleum ether or acetic acid.) Water-insoluble acids can be partially purified by dissolution in N sodium hydroxide solution and precipitation with dilute mineral acid. If the acid is required to be free from sodium ions, then it is better to dissolve the acid in hot N ammonia, heat to ca 80°, adding slightly more than an equal volume of N formic acid and allowing to cool slowly for crystallisation. Any ammonia, formic acid or ammonium formate that adhere to the acid are removed when the acid is dried in a vacuum — they are volatile. The separation and purification of naturally occurring fatty acids, based on distillation, salt solubility and low temperature crystallisation, are described by K.S.Markley (Ed.), Fatty Acids, 2nd Edn, part 3, Chap. 20, Interscience, New York, 1964. 

Barium tetrathionate [82203-66-5] M 361.6. Purified by dissolution in a small volume of water and ppted with EtOH below 5°. After drying the salt was stored in the dark at 0°. 

In small portions, just sufficient to maintain the blue color, 5.0 g. (0.22 gram atom) of clean, metallic sodium is added with vigorous stirring. After dissolution is complete (Note 3), a solution of 23.4 g. (0.20 mole) of indole (Note 4) in 50 ml. of anhydrous ether is added slowly and then, after an additional 10 minutes, a solution of 31.2 g. (0.22 mole) of methyl iodide in an equal volume of anhydrous ether is added dropwise. Stirring is continued for a further 15 minutes. Fhe ammonia is allowed to evaporate (Note 5), 100 ml. of water is added, followed by 100... 

Density Separation Storage Volume Required Size Modification or Separation Size Reduction Dissolution... 

Although crude cyanoamidine (10) can be used for many reactions, reduction to the 2-formyl-A-norsteroid (11) is most satisfactory when purified material is employed. The crude cyanoamidine is stirred for about 15 min with boiling toluene (120 ml/g of steroid) to effect dissolution, the hot solution is filtered quickly through fluted paper, and the filtrate is cooled and diluted with an equal volume of petroleum ether. The mixture is cooled for 0.5 hr in ice, affording from 25 g of crude material about 18 g of colorless 2a-(A-pyrrolidinylcyanoiminomethyl)-A-nor-5a-androstan-17 -ol (10) mp 252-255° (anal, sample mp 262-263°, from benzene-hexane 250 m ... 

The interpretation of these remarkable properties has excited considerable interest whilst there is still some uncertainty as to detail, it is now generally agreed that in dilute solution the alkali metals ionize to give a cation M+ and a quasi-free electron which is distributed over a cavity in the solvent of radius 300-340 pm formed by displacement of 2-3 NH3 molecules. This species has a broad absorption band extending into the infrared with a maximum at 1500nm and it is the short wavelength tail of this band which gives rise to the deep-blue colour of the solutions. The cavity model also interprets the fact that dissolution occurs with considerable expansion of volume so that the solutions have densities that are appreciably lower than that of liquid ammonia itself. The variation of properties with concentration can best be explained in terms of three equilibria between five solute species M, M2, M+, M and e ... 

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