Content and Hygroscopicity

The effects of moisture content in drug substances iancthed dosage form have been widely studied. Static moisture content can be determined by many methods like Karl Fisher titration, loss on drying (LOD), and TGA. Dynamic hygroscopicity of a drug substance has beerLcWaato four 

Salt selection may help to improve various properties of a drug substance such as bioavailability, stability, and manufacturability. 

Salt screening is often conducted in parallel to the polymorph screening in case a scalable crystallization process for the drug is not found. Chapter 11 in this book is devoted to this topic, and the reader is directed there for a detailed discussion. 

The importance of polymorphism in pharmaceuticals cannot be overemphasized. Some crystal structures contain molecules of water or solvents, known as hydrates or solvates, respectively, and they are also called as pseudopolymorphs. Identifying all relevant polymorphs and solvates at an early stage of development for new chemical entities has become a well-accepted concept in pharmaceutical industry. For poorly soluble compounds, understanding their polymorphic behavior is even more important since solubility, crystal shape, dissolution rate, and bioavailability may vary with the polymorphic form. Conversion of a drug substance to a more thermodynamically stable form in the formulation can signiLcantly increase the development cost or even result in product failure. 

Preformulation should include rigorous studies to determine the number of polymorphs that exist, relative degree of stability of the various polymorphs, solubilities, method of preparation of each form, effect of micronization and tableting, and interaction with formulation ingredients. 

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In spite of the variability of the sum calculated from the nitrogen content and hygroscopicity the effect of the nitrogen content on the hygroscopicity can be expressed by a straight line. In Fig. 109 (after de Pauw) straight-lines corresponding with different relative moistness of atmosphere (f/F) are shown. 

The influence of sorbed moisture on chemical stability and the flow and compaction of powders and granulations is well established. The moisture content and hygroscopicity of excipients is particularly important as total product processing as well as finished product stability can be affected. Hygroscopicity, moisture-sorption isotherms, and equilibrium moisture content can be determined by thermogravimetric analysis and Karl Fisher titration methods. 

Cellulose filters (Whatman 41, Whatman, USA) were selected for this study because of their low intrinsic metal content and hygroscopic character (Dams et al. 1972). These filters are widely used in a range of applications including filtering of solutions and airborne particulate matter collection. The cellulose filters used for this work have a dimension of 20 x 25 cm 2 x 1 cm sections were cut using stainless steel scissors to fit in the sample cell of the LA system. 

Potassium nitrate is being used increasingly on intensive crops such as tomatoes, potatoes, tobacco, leafy vegetables, citms, and peaches. The properties that make it particularly desirable for these crops are low salt index, nitrate nitrogen, favorable N K20 ratio, negligible CU content, and alkaline residual reaction in the soil. The low hygroscopicity of KNO (Table 9) leads to its use in direct appHcation and in mixtures. It is an excellent fertilizer but the high cost of production limits its use to specialty fertilizers. 

Almost all tests carried out to study the starting process of atmospheric corrosion have been performed in a surface without corrosion products however, in real conditions, the metal is covered with corrosion products after a given time and these products begin to play its role as retarders of the corrosion process in almost all cases. Corrosion products acts as a barrier for oxygen and contaminants diffusion, the free area for the occurrence of the corrosion is lower however, the formation of the surface electrolyte is enhanced. Only in very polluted areas the corrosion products accelerate the corrosion process. Water adsorption isoterms were determined to corrosion products formed in Cuban natural atmospheres[21]. Sorption properties of corrosion products (taking into account their salt content-usually hygroscopics) determine the possibilities of surface adsorption and the possibility of development of corrosion process... 

Chowhan [9] defined different pathways of physical instability of tablet formulations. These physical paths may involve one or more complex physical processes, e.g. change in polymorphism, crystallization, vaporization and adsorption. These pathways and thus the physical tablet parameters, are influenced by different types of variables formulation variables (e.g. solubility and hygroscopicity), in-process variables (e.g. moisture content) and aging variables (e.g. temperature and relative humidity). 

Another potential effect is if one species affects the concentration of others due to chemical interactions. If the concentration of a species that is hygroscopic changes, the water content and average index of refraction for the particle may change simultaneously. For example, a reduction of about 7% in the index of refraction due to increased hydration can lead to a change in the scattering efficiency of as much as 34% (Hegg et al., 1993). 

Electrical Resistance Moisture Meters. The electrical resistance of wood is extremely sensitive to its moisture content, approximately doubling for each 1% decrease in moisture content over the hygroscopic range of moisture contents. The development of a successful resistance moisture meter may be attributed primarily to the pioneering work of Stamm (9) who first measured this relationship quantitatively. Because of the nature of electrical conduction in wood there is also a strong increase in resistivity with a decrease in wood temperature. Figure 1 illustrates how the electrical resistivity of wood varies with both moisture content and temperature. 

Moisture content slightly hygroscopic. A well-defined crystalline hydrate is not formed although surface moisture may be picked up or contained within small pores in the crystal structure. At relative humidities between about 15% and 65%, the equilibrium moisture content at 25°C is about 2.0%. At relative humidities above about 75%, tribasic calcium phosphate may absorb small amounts of moisture. Particle size distribution Tribasic calcium phosphate powder typical particle diameter 5-10 pm 98% of particles <44 pm. 

The vitreous B2O3 is colourless, transparent and hygroscopic. It can be prepared by dehydration of H3BO3 at 266 °C —270 C under a reduced pressure of 130 — 260 Pa. The removal of water by heating H3BO3 in air is quite difficult and even the melt contains considerable amounts of residual water.The final H2O content after fusion at 700,1100 and 1200 °C is 0.25, 0.17 and 0.14% respectively (Poch, 1964). As a result of the H2O content, the data on the basic properties (e.g. those on viscosity and thermal expansion coefficient) exhibit some differences. The viscosity curve shown in Fig. 7 should serve for rough orientation only. More detailed data are reported by Bruckner (1964), for example. 

Copovidone forms soluble films, independently of the pH, regardless of whether it is processed as a solution in water or in organic solvents, or as a powder. It differs from povidone as a film-forming agent in that it is less hygroscopic (see Section 4.2.4.4) and has greater plasticity and elasticity. At the same time the films are also less tacky. The glass transition temperature depends on the moisture content, and at 103°C for dry copovidone, is also below that of dry povidone K 30 (i68°C). 

Results of the char analyses are given in Table II. They are only presented for two specific experiments since the characteristics did not vary considerably with reactor temperature or residence times. The calorific value of the straw char was higher than that of the stover char by about 20%. The calorific value of the straw char on a unit weight basis was about 1.6 times greater than the straw feed and the calorific value of the stover char was about 1.4 times greater than the stover feed. Further characterization of the char will be carried out in Phase II. Of particular interest are the burning characteristics, hygroscopicity, ash and acid insoluble ash content and measured calorific value. 

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