Osmotic adjustment pressure

Fig. 4. Whole-plant fresh weight and leaf osmotic adjustment of Thino-pyrum bessarabicum as a function of time following the gradual addition of 250 mol m NaCl to the culture solution. Fresh weight = control, O = 250 mol m NaCl. Leaf sap osmotic pressure = 250molm NaCl.

When data on the amphidiploid and the hexaploid wheats are considered (Table 5), the former being substantially more salt tolerant in hydroponic culture, then again several points are noted. First, the sap osmotic pressure in the young leaves is least in the tolerant amphidiploid. Secondly, Na" and Cl levels are also lower in the juvenile amphidiploid leaves. These data imply that minimal osmotic adjustment is more beneficial than apparently complete osmotic adjustment. 

Ophthalmic Dosage Forms. Ophthalmic preparations can be solutions, eg, eye drops, eyewashes, ointments, or aqueous suspensions (30). They must be sterile and any suspended dmg particles must be of a very fine particle size. Solutions must be particle free and isotonic with tears. Thus, the osmotic pressure must equal that of normal saline (0.9% sodium chloride) solution. Hypotonic solutions are adjusted to be isotonic by addition of calculated amounts of tonicity adjusters, eg, sodium chloride, boric acid, or sodium nitrate. 

Equation (22) has been confirmed by a variety of techniques including neutron scattering, dynamic light scattering, and osmotic pressured measurements [23]. As concentration increases the concentration blob decreases in size until the Kuhn length is reached and the coil displays concentrated or melt Gaussian structure. The coil accommodates concentrations between the overlap and concentrated through adjustment of the concentration blob size. 

Special care has to be taken if the polymer is only soluble in a solvent mixture or if a certain property, e.g., a definite value of the second virial coefficient, needs to be adjusted by adding another solvent. In this case the analysis is complicated due to the different refractive indices of the solvent components [32]. In case of a binary solvent mixture we find, that formally Equation (42) is still valid. The refractive index increment needs to be replaced by an increment accounting for a complex formation of the polymer and the solvent mixture, when one of the solvents adsorbs preferentially on the polymer. Instead of measuring the true molar mass Mw the apparent molar mass Mapp is measured. How large the difference is depends on the difference between the refractive index increments ([dn/dc) — (dn/dc)A>0. (dn/dc)fl is the increment determined in the mixed solvents in osmotic equilibrium, while (dn/dc)A0 is determined for infinite dilution of the polymer in solvent A. For clarity we omitted the fixed parameters such as temperature, T, and pressure, p. 

Make the medium shown in Table 1 (200 mL for 10 Petri dishes). For the growth of pollen tubes in vitro, calcium and borate are generally required. Sucrose is also added to the medium, mainly for the purpose to adjust the osmotic pressure it is unclear whether the external sucrose plays a role... 

Several factors of design and manufacture are of great importance sterility, absence of pyrogens and foreign particulate matter, and tonicity. The last, when adjusted to the osmotic pressure of body fluids in the case of aqueous solutions, reduces the risk of tissue irritation and pain,... 

Figure 2.3 Typical osmotic pressure data, where solvent A is a very good solvent (strong polymer-solvent interactions), B is a moderately good solvent, and C is a 0 solvent (in which polymer-solvent interactions have been adjusted to nullify the excluded volume effect).31a Reprinted with permission from J. E. Mark, Physical Chemistry of Polymers, ACS Audio Course C-89, American Chemical Society, Washington, DC, 1986. Copyright 1986, American Chemical Society.

Pyranine has been used to study the proton dissociation and diffusion dynamics in the aqueous layer of multilamellar phospholipid vesicles [101], There are 3-10 water layers interspacing between the phospholipid membranes of a multilamellar vesicle, and their width gets adjusted by osmotic pressure [102], Pyranine dissolved in these thin layers of DPPC and DPPC+cholesterol multilamellar vesicles were used as a probe for the study. Before the photoreleased proton escapes from the coulombic cage, the probability of a proton excited-anion recombination was found to be higher than in bulk. This was attributed to the diminished water activity in the thin layer. It was found that the effect of local forces on proton diffusion at the timescale of physiological processes is negligible. 

Many cestodes appear to behave like osmometers, and when placed in an environment with a different osmotic pressure can only adjust their internal osmotic pressure by varying their body volume. Moniezia, Hymenolepis, Schistocephalus and Callibothrium change their weight almost arithmetically in response to a change in external osmotic pressure (796). 

The alga Phaerodactilum tricornutum was found to respond to hyperosmotic stress by a marked elongation of PolyP and a decrease in its total amount, while exposure to hypoosmotic stress resulted in a higher content of shorter PolyPs and an increased total PolyPs content (Leitao et al., 1995). It is probable that, such variations might allow the adjustment of the intracellular osmotic pressure to an extracellular one. 

The volume of urine produced each day is very variable since the kidney maintains water balance in the body by adjusting the excretion of water, keeping the osmotic pressure of body fluids constant. Approximately 1.5 to 21 of urine are usually excreted each day. 

The combination of active drug, preservative, and vehicle usually results in a hypotonic formulation (< 290 mOsm). Simple or complex salts, buffering agents, or certain sugars are often added to adjust osmolarity of the solution to the desired value. An osmolarity of 290 mOsm is equivalent to 0.9% saline, and this is the value sought for most ophthalmic and intravenous medications.The ocular tear film has a wide tolerance for variation in osmotic pressure. However, increasing tonicity above that of the tears causes immediate dilution by osmotic water movement from the eyelids and eye. Hypotonic solutions are sometimes used to treat dry eye conditions and to reduce tear osmolarity from abnormally high values. 

Modern osmometers reach equilibrium pressure in 10-30 min and indicate the osmotic pressure automatically. Several types are available. Some commonly used models employ sensors to measure. solvent flow through the membrane and adjust a counteracting pressure to maintain zero net flow. Other devices use strain gauges on flexible diaphragms to measure the osmotic pressure directly. 

The four colligative properties that are of importance are 1) the vapor pressure lowering 2) the elevation of boiling point 3) the freezing-point depression and 4) the osmotic pressure. An attempt is made below to describe qualitatively and quantitatively each colligative property of solutions, with an emphasis on their interrelationship and their application later in measurement and adjustment of the tonicity of solutions, with particular reference to parenteral formulations. Although theoretical derivations based on thermodynamics can be used to show how each of the colligative properties of solution arises and relate to each other, textbooks on physical chemistry for theoretical derivations are recommended. 

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