Solvents and impurities

When the samples have been withdrawn from the vessels, suitable analytical separations must be available to analyze the reaction. This would include starting materials, products, impurities, and solvents, as appropriate. Quantitations may need to be developed for key components. Karl Fischer titrations may be needed... 

As a starting point for considering the effect of impurity and solvent on crystallization, the growth and interaction process is examined in the framework of the fundamental solid-state, interfacial, and liquid phase (solute-solvent-impurity) chemistry. The solid-state chemistry is specific to a given crystalline material and the nature of the bonds (e.g., ionic, covalent, van der Waals, etc.) that hold the crystal structure together. A complete description of the solid-state aspects of crystal growth is beyond the scope of this... 

The most common sample forms used for the measurement of electrical properties are pressed pellets, thin films, and single crystals. Electrical measurements on pellets are often difficult to interpret because of the presence of polycry staUinity, grain boundaries, large surface area, and unknown amounts of adsorbed gases. Films are useful in some instances, but in many cases also cause uncertainties because of poly cry staUinity. Electrical properties are most easUy and reUably interpreted with single crystals free from unintentional impurities and solvent occlusions. 

If absorption by impurities and solvent can be neglected, the quantum yield of the solution can be taken as that of the dye (tjfj = Unfortunately, the precision with which thermooptic coefficients are known is inadequate for precise measurements of the quantum yield via Eqs. (6)-(9). To circumvent this problem, Brannon and Magde [19] suggested using a nonfluorescent compound as reference. Thus in addition to the sample, designated below by superscript s, the reference compound, denoted by a superscript r, is measured under the same conditions (solvent, temperature, etc.). For this reference P bs equals P,b, and by combining Eqs. (6b), (7a) and (9), the following expression for the quantum yield is obtained ... 

Bundgaard, H. Influence of an acetylsalicylic anhydride impurity on the rate of dissolution of acetylsalicylic acid. J. Pharm. Pharmacol. 1974, 26, 535-540. Klug, D.L. The influence of impurities and solvents on crystallization. In Handbook of Industrial Crystallization Myerson, A.S. Ed. Butterworth-Heinemann Boston, 1993 65-87. 

Peak. If the user selects this function, the screen is changed as shown in Figure 9. All peaks which are detected previously are shown by vertical lines. The impurity peak(s) and solvent peak(s) which have been designated in the previous step are also shown and they may be changed by means of IMPURITY and SOLVENT subcommands. The two subcommands ADD and DELETE are used for adding and deleting peaks arbitrarily. 

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