Osmotic value importance

To isolate intact organelles, it is important for the homogenization solution to be isotonic—I e the osmotic value of the buffer has to be the same as that of the interior of the cell. If hypotonic solutions were used, the organelles would take up water and burst, while in hypertonic solutions they would shrink. 

In the formulation of preparations for the oropharynx, taste and texture are features that are important for the acceptance by the patient. Pharmacy preparation can play an important role, because of the advantage that preparations can be tailor made according to the specific situation or taste of the patient. For instance, chemotherapy and several other active substances, may cause dry mouth and stomatitis, and mouthwashes or gels can relieve these problems. However, they should not cause irritation and must be accepted by the patient. This has to be kept in mind when choosing a vehicle, or the pH or the osmotic value of a preparation. 

The volume of enemas may vary from a few millilitres (micro-enema) to more than 100 mL, mainly depending on the intended effect systemic or local. For large-volume enemas water is commonly used and a water-soluble form of the active substance is preferred. The solubility may be increased by addition of co-solvents, to be applied in small volume enemas. If a soluble active substance or an adequate co-solvent cannot be found, a suspension may be prepared. If this is also not an option, a lipophilic vehicle may be chosen. Choice of pH depends on the chosen form of the active substance and is important for the absorption. Excipients may be added to correct the osmotic value, to increase the viscosity, to prevent oxidation or for preservation. 

Registration authorities invite the manufacturer to include pH and osmotic value of the product in the packaging leaflet The pH and the osmotic value of the undiluted as well as the ready to administer product are important in order to estimate the chance of phlebitis. The information about pH is also useful for investigating the possibility of mixing reconstituted products. 

Irrigations to rinse a surgical area or a deep wound should be iso-osmotic. For disinfection or cleansing of superficial wounds this is not strictly necessary. Historically, a sterile hyperosmotic solution (NaCl 3 %, for example) is prepared for rinsing superficial moist wounds and bedsores. Hypertonicity is in fact the mechanism of action the solution has a desiccating effect. For irrigations for the bladder iso-osmosis is less important. Hypo-osmosis is more problematic than hyper-osmosis, because the osmotic value of urine is twice to trice the osmotic value of blood [4]. 

The osmotic value of a solution (see Sect. 18.5) may be an important quality parameter for parenterals, but also for eye or nose drops which should, in principle, be isotonic. Values outside the physiologic limits point to a deviation in the declared composition. The osmolality will be studied in the design phase of the preparation and later often will only be checked as in-process control. 

Reciprocals of the critical temperatures, i.e., the maxima in curves such as those in Fig. 121, are plotted in Fig. 122 against the function l/x +l/2x, which is very nearly 1/x when x is large. The upper line represents polystyrene in cyclohexane and the lower one polyisobutylene in diisobutyl ketone. Both are accurately linear within experimental error. This is typical of polymer-solvent systems exhibiting limited miscibility. The intercepts represent 0. Values obtained in this manner agree within experimental error (<1°) with those derived from osmotic measurements, taking 0 to be the temperature at which A2 is zero (see Chap. XII). Precipitation measurements carried out on a series of fractions offer a relatively simple method for accurate determination of this critical temperature, which occupies an important role in the treatment of various polymer solution properties. 

A semi-permeable membrane, which is unequally permeable to different components and thus may show a potential difference across the membrane. In case (1), a diffusion potential occurs only if there is a difference in mobility between cation and anion. In case (2), we have to deal with the biologically important Donnan equilibrium e.g., a cell membrane may be permeable to small inorganic ions but impermeable to ions derived from high-molecular-weight proteins, so that across the membrane an osmotic pressure occurs in addition to a Donnan potential. The values concerned can be approximately calculated from the equations derived by Donnan35. In case (3), an intermediate situation, there is a combined effect of diffusion and the Donnan potential, so that its calculation becomes uncertain. 

It can now be used for the extremely important purpose of calculating calcium sulphate and 4,000 dyne/cm. for barium sulphate. These figures entirely confirm the conclusion to which we have come on general grounds, that the surface tensions of solids must have high values. The applicability of the Ostwald-Hulett formula is limited, since it is based on Van t Hoff s equation for osmotic pressure, which only holds for small concentrations and, therefore, in the present case, for low solubilities. 

V, is the molar volume of polymer or solvent, as appropriate, and the concentration is in mass per unit volume. It can be seen from Equation (2.42) that the interaction term changes with the square of the polymer concentration but more importantly for our discussion is the implications of the value of x- When x = 0.5 we are left with the van t Hoff expression which describes the osmotic pressure of an ideal polymer solution. A sol vent/temperature condition that yields this result is known as the 0-condition. For example, the 0-temperature for poly(styrene) in cyclohexane is 311.5 K. At this temperature, the poly(styrene) molecule is at its closest to a random coil configuration because its conformation is unperturbed by specific solvent effects. If x is greater than 0.5 we have a poor solvent for our polymer and the coil will collapse. At x values less than 0.5 we have the polymer in a good solvent and the conformation will be expanded in order to pack as many solvent molecules around each chain segment as possible. A 0-condition is often used when determining the molecular weight of a polymer by measurement of the concentration dependence of viscosity, for example, but solution polymers are invariably used in better than 0-conditions. 

The thermodynamic approach does not make explicit the effects of concentration at the membrane. A good deal of the analysis of concentration polarisation given for ultrafiltration also applies to reverse osmosis. The control of the boundary layer is just as important. The main effects of concentration polarisation in this case are, however, a reduced value of solvent permeation rate as a result of an increased osmotic pressure at the membrane surface given in equation 8.37, and a decrease in solute rejection given in equation 8.38. In many applications it is usual to pretreat feeds in order to remove colloidal material before reverse osmosis. The components which must then be retained by reverse osmosis have higher diffusion coefficients than those encountered in ultrafiltration. Hence, the polarisation modulus given in equation 8.14 is lower, and the concentration of solutes at the membrane seldom results in the formation of a gel. For the case of turbulent flow the Dittus-Boelter correlation may be used, as was the case for ultrafiltration giving a polarisation modulus of ... 

The total electro-osmotic coefficient = Whydr + mo includes a contribution of hydrodynamic coupling (Whydr) and a molecular contribution related to the diffusion of mobile protonated complexes—namely, H3O. The relative importance, n ydr and depends on the prevailing mode of proton transport in pores. If structural diffusion of protons prevails (see Section 6.7.1), is expected to be small and Whydr- If/ ori the other hand, proton mobility is mainly due to the diffusion of protonated water clusters via the so-called "vehicle mechanism," a significant molecular contribution to n can be expected. The value of is thus closely tied to the relative contributions to proton mobility of structural diffusion and vehicle mechanism. ... 

Another important application of experimentally determined values of the osmotic second virial coefficient is in the estimation of the corresponding values of the Flory-Huggins interaction parameters x 12, X14 and X24. In practice, these parameters are commonly used within the framework of the Flory-Huggins lattice model approach to the thermodynamic description of solutions of polymer + solvent or polymer] + polymer2 + solvent (Flory, 1942 Huggins, 1942 Tanford, 1961 Zeman and Patterson, 1972 Hsu and Prausnitz, 1974 Johansson et al., 2000) ... 

Tire evaluation of Mr is often of critical importance. Minimum values of Mr can often be computed from the content of a minor constituent, e.g., the tryptophan of a protein or the iron of hemoglobin. However, physicochemical techniques provide the basis for most measurements.177 Observations of osmotic pressure or light scattering can also be used and provide determinations of Mr that are simple in principle, but which have pitfalls.178... 

Recently, Nyquist et al. [39] tried to develop a theory for rods of finite size. These authors used a two-state model for the counterions and employed a random phase approximation in order to calculate the osmotic coefficient (j) of rod-like polyelectrolytes [39]. An important goal of this work was to reproduce in the zero density limit the correct osmotic coefficient of 1 instead of the Manning limiting value which is due to the unphysical infinite rod assumption employed. The model presented in ref. [39], however, seems to overestimate considerably the osmotic coefficient when compared to experimental data (see below Sect. 4.2). 

After all drug is dissolved, the osmotic pressure decays and the beads shrink to their equilibrium swelling value, as observed for beads with high water swelling (11,12) during this second release phase normal Fickian diffusion kinetics becomes more important, characterized by a very low rate which depends on the hydro-philicity of the polymer. 

The osmolality of tears is of prime importance, since optical integrity of the cornea is significantly influenced by the tonicity of the tears. The normal osmolality of tears varies from 290 to 310 mOsmkg-1, which is almost equivalent to that of normal saline solution. Variations in osmotic pressure between 100-640 mOsmkg 1 appear to be well tolerated by the eye beyond these values irritation takes place, eliciting reflex tears and reflex blinking. 

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