Precipitation by changing

The more disagreeable and troubling side-effect of long-term neuroleptic treatment is tardive dyskinesia. This occurs after variable duration of treatment, and may be precipitated by changing doses, and repetitive stopping and starting drugs. Its mechanism is not well known, and it may improve when... 

Microemulsion A microemulsion process is the process that two immiscible liquids will go through a dispersion stage where both liquids are stabilized by the surfactant molecules. For example, oil and water are two immiscible liquids. The disperse phase of oil will be surrounded by surfactant molecules. With the desired reactants in the solution, the microdroplets will form and then break to precipitate in the micelles. Acetone and ethanol can be used as solvent for microemulsions to extract the precipitate by changing the structure. Figure 1.4 shows the nanorod synthesis process (Lu et al., 2007). 

By precipitation through boiling radionuclide solution with cleaned sand, or precipitation by changing pH... 

Specific adsorption. Enzymes showing acidic properties can be removed from solution by addition of an insoluble basic adsorbent, usually aluminium hydroxide. Basic enzymes can be reihoved by use of an acidic adsorbent, usually kaolin. The adsorbed enzyme is liberated, or eluted, from the precipitate by changing the pH of the mixture or by addition of a more acceptable adsorbent. 

HPC is available in a number of viscosity grades, ranging from about 3000 mPa-s(=cP) at 1% total soHds in water to 150 mPa-s(=cP) at 10% total sohds. HPC solutions are pseudoplastic and exceptionally smooth, exhibiting Htde or no stmcture or thixotropy. The viscosity of water solutions is not affected by changes in pH over the range of 2 to 11. Viscosities decrease as temperature is increased. HPC precipitates from water at temperatures between 40 and 45°C. Dissolved salts and other compounds can profoundly influence the precipitation temperature (50,81). 

Precipitatioa (2,13—17) techniques employ a combination of nucleation and growth iaduced by adding a chemical precipitant, or by changing the temperature and/or pressure of the solution. Chemical homogeneity is controlled by controlling the rate of precipitation. FFeterogeneous precipitation iavolves the precipitation of a soHd of different composition from the solution, and the composition of the precipitate may change as precipitation continues. Coprecipitation iavolves the simultaneous precipitation of similar size cations ia a salt as a soHd solutioa. 

Almost anyone who has at some time in his life met some reverses is familiar with depression. In the normal course of events, changing circumstances will soon lead to the replacement of this state of mind by a more pleasant one. There exist, however, a set of pathologic states in which depression feeds on itself in a destructive cycle. Individuals affected with this syndrome— whether precipitated by outside events or not—eventually find it most difficult to function. The advent of antidepressant drugs, first the MAO inhibitors and more recently the tricyclic antidepressants, have made this syndrome amenable to treatment. 

An alternative procedure for removing an ion from solution is to change its identity by changing its oxidation state. The metal ions in very insoluble heavy metal sulfide precipitates can be dissolved by oxidizing the sulfide ion to elemental sulfur. For example, copper(II) sulfide, CuS, takes part in the equilibrium... 

The synthetic approach is very simple and does not require any special set up. In a typical room temperature reaction, 1.0 mL aqueous solution of cadmium chloride was added to 20 mL aqueous solution of soluble starch in a 50 mL one-necked round-bottom flask with constant stirring at room temperature. The pH of the solution was adjusted from 6 to 11 using 0.1 M ammonia solution. This was followed by a slow addition of 1.0 mL colourless selenide ion stock solution. The mixture was further stirred for 2 h and aged for 18 h. The resultant solution was filtered and extracted with acetone to obtain a red precipitate of CdSe nanoaprticles. The precipitate was washed several times and dried at room temperature to give a material which readily dispersed in water. The same procedure was repeated for the synthesis of PVA and PVP - capped CdSe nanoparticles by replacing the starch solution with the PVA and PVP polymers while the synthesis of elongated nanoparticles was achieved by changing the Cd Se precursor ratio from 1 1 to 1 2. The synthesis of polymer capped ZnSe nanoparticles also follows the same procedure except that ZnCb solution was used instead of CdCb solution. 

Depression is a common problem in patients with epilepsy, with approximately 30% having symptoms of major depression at some point.34 Patients with epilepsy should be routinely assessed for signs of depression, and treatment should be initiated if necessary. Certain AEDs may exacerbate depression, for example levetirac-etam and phenytoin. Other AEDs (e.g., lamotrigine, carba-mazepine, and oxcarbazepine) maybe useful in treating depression. Changes in mood can be precipitated by addition or discontinuation of an AED. If treatment for depression is necessary, caution should be exercised in choosing an agent that does not increase seizure frequency and does not interact with AEDs. 

Applications Caceres et al. [114] compared various methods for extraction of Tinuvin 770 and Chimas-sorb 944 from HDPE pellets, namely room temperature diffusion in CHC13 (20 % extraction), ultrasonica-tion (20% extraction), Soxtec extraction with DCM (nonsolvent) (50 % extraction), dissolution (dichloroben-zene)/precipitation (2-propanol) (65-70% recovery) and boiling under reflux with toluene (solvent) at 160 °C (95 % extraction). By changing conditions (nature of solvent, T, t) similar comparisons do not have much added value. Table 3.6 compares the results of reflux extraction and MAE for additives in LDPE [115]. 

Table 7.89 lists the main characteristics of MDHPLC (see also Table 7.86). In MDHPLC the mobile-phase polarity can be adjusted in order to obtain adequate resolution, and a wide range of selectivity differences can be employed when using the various available separation modes [906]. Some LC modes have incompatible mobile phases, e.g. normal-phase and ion-exchange separations. Potential problems arise with liquid-phase immiscibility precipitation of buffer salts and incompatibilities between the mobile phase from one column and the stationary phase of another (e.g. swelling of some polymeric stationary-phase supports by changes in solvents or deactivation of silica by small amounts of water).

---