Suspension equilibration

One of the most useful and unambiguous methods to assess the relative stabUity of two or more forms is suspension equilibration or slurry experiments. If a mixture of two forms is slurried in a solvent at a constant temperature for a long enough period of time, only two outcomes are possible  

The slurry technique can also be used to determine the critical water activity of hydrate formation. If a mixture of hydrate and anhydrate is slurried in a solvent/-water mixture of known water activity, the hydrate has to convert to the anhydrate when the water activity of the solvent is below the critical water activity of hydrate 

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In Figure 5.7, the free energy of the dihydrate of carbamazepine is plotted as a function of the water activity of the environment. The critical water activity of 0.6 was determined by suspension equilibration experiments, as described in Section 5.5.2. 

Crystallization experiments from solution, using several techniques (e.g., (i), (ii), (iii), and (v) in Table 5.1) with a variety of solvents and solvent mixtures. Due to the practical relevance of hydrates, water and water/solvent mixtures should always be included. Suspension equilibration and slow coohng experiments play a particular role in finding the thermodynamically stable form, which is often the most important aim of a polymorph screen. 

Fig. 18 Raman spectra of silver nanoparticle-5X-aminodextran-PS bead with rhodamine 6G (top 3 spectra, top to bottom, 1% w/v solids bead suspension, equilibrated with 1 x 10 M, 5 x 10 M, and 1 X R6G, respectively, followed by wash and lOx dilution with deionized water,...

Following the completion of the polymerization process, the beaded polymer is recovered from the suspension mixture and freed from the stabilizer, diluents, and traces of monomers and initiators. For laboratory and small-scale preparation, repeated washings with water, methanol, or acetone are appropriate. Complete removal of the monomer diluent, solvents, and initiator, especially from macroporous resin, may require a long equilibration time with warm methanol or acetone. In industry, this is usually accomplished by stream stripping. 

Fig. 2.2 Assay of luciferase by the injection of FMNH2. The assay was initiated by the injection of 1 ml of 50 JtM FMNH2 solution into 1 ml of air equilibrated buffer, pH 7.0, containing 0.1% BSA, luciferase, and 20 gl of 0.01% sonicated suspension of dodecanal. From Baldwin et al., 1986, with permission from Elsevier.

Baker s yeast suspension (20% ww/v original cells) was pumped to the bead mill at a flow rate of 280 cm h 1 within the BRG 4.5 cm inner diameter contactor. Then, the disruptate from the mill was directly introduced to the pre-equilibrated fluidised bed containing ZSA II-CB and Macrosorb K4AX-CB. 

Reeve Angel and Co., Clifton, N.J. 07104) is equilibrated with Developer A, and the pH of the stirred suspension Is adjusted to 6.1 with 6 N hydrochloric acid. Several settlings in Developer A should be made In order to remove fine particles. Supernatant buffer and settled resin should be equal In volume for the slurry that Is used to pour the column. One column,... 

The culture broth was recovered after 72 h of fermentation, the biomass removed and the total protein content measured. Broth aliquots with a protein content of 1 mg were collected and their pH regulated at different values ranging from 3.5 to 8.0. To each broth fraction, 50 mg of the microspheres sample, previously equilibrated at the corresponding pH, was added and the suspension left under stirring overnight. Then, the microspheres were removed by centrifugation and the protein content and the PG activity were assayed on the resulting supernatant. 

The determination of partition coefficients using liposomes as a lipid phase require that the sample be equilibrated with a suspension of liposomes, followed by a separation procedure, before the sample is quantitated in the fraction free of the lipid component. 

The photodynamic effect of chloroaluminum(III) phthalocyanine ((47), with C1A1 in place of Zn), a commercial product, was reported by Ben-Hur and Rosenthal.302 The photosensitizer was delivered in ethanol to cultures of Chinese hamster fibroblasts. After equilibration (16 h), exposure to visible light (fluence rate 64 Wm-2) of a suspension in PBS for 2 min gave a 3 log kill. Lack of water solubility is a problem, and for in vivo PDT of EMT-6 mammary tumors in mice a Cremophor emulsion was employed.303 The compound was a more effective PDT sensitizer than... 

Initial studies were made with the Rank Bros, electrophoresis unit, using the dilute supernatant suspension over a dispersion of 3.33g of carbon black per liter of dodecane equilibrated for 24 hours with the added 0L0A-1200. The electrophoretic mobility (u) of 1-3 pm clumps of particles was observed at a field of 100 volts per centimeter. The zeta-potentials ( ) were calculated... 

Z-4A), and zeolite H-ZSM-5. The interlayer distance varied by the intercalation was determined from X-ray diffraction patterns. The interlayer space of the crystalline zeolite is separated by the three-dimensional cage structures. The mean diameters of particles were approximately 1 ym. Such small particles formed very stable suspensions with no sign of sedimentation over the time course of the kinetic measurements. The analytical techniques used to obtain the equilibrium concentration are described elsewhere (10-22). All samples were equilibrated for 24-72 h after preparation. The temperature was controlled at 25 °C. 

Oxidation Studies. These studies were performed at 25+0.2°C in a carbonate buffered 0.1 M NaClO solution. The buffer was equilibrated with air or an 02/C02 gas mixture for at least 24 hours. The pH was adjusted to 8.3 using HCIO, NaOH, or Na2C03. Where y-FeOOH was present the suspension was deaerated by bubbling N2/C02 for 1 hour, the Mn(II) was added and was allowed to equilibrate with the solid for 30 minutes and then the oxidation was commenced by switching to 02/C02 or air bubbling. Where no solid was present the solution was not deaerated. The rate of oxidation was monitored by following the loss of filterable Mn. 

The supernatant was supplemented with NaCl to a concentration of 0.5 m NaCl and mixed with 35 mL of Novagen Fractogel His-Bind resin (pre-equilibrated and loaded with Ni as recommended by the manufacturer). The suspension was gently mixed for 30 min and then manually loaded into a 500 mL glass column and packed under 1.5 bar Ar pressure. 

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