Emulsion partition coefficient

The model mouth and the RAS were used in two separate studies to determine the release of aroma from two separate model emulsion systems with known amounts of five aroma compounds, while varying the saliva volumes and mastication rates. In each study, only the effects of mastication and saliva volume on the release of aroma at one emulsion-to-saliva ratio and one mastication rate, respectively, are presented and discussed. Before both studies, static headspace analysis was used to determine the gas-emulsion partition coefficients of the five aroma compounds above the emulsions, while varying the emulsion-to-saliva ratio. 

Significance of Partition Coefficient of a Preservative in Cosmetic Emulsion, by H S Bean et all, American Perfumer and Cosmetics, Vol. 85, March, 1970... 

Other fatty acids as absorption enhancers have been reported. Ogiso et al. [112] demonstrated that lauric acid (C12) produced the largest increase in permeation rate, penetration coefficient, and partition coefficient of propranolol. Onuki et al. [113] reported that docosa-hexaenoic acid (DHA) has a strong insulin permeability enhancement effect and little toxicity, compared to oleic acid and eicosapentaenoic acid (EPA) using a water-in-oil-in-water (W/O/W) multiple emulsion with no or little mucosal damage. 

It has to be clear that, once diluted and injected (or administered in ocular and other routes), the emulsion stability and fate are determined by three measurable parameters. The first is the partition coefficient of each emulsion component (including added drugs and agents) between the emulsion assembly and the medium. To some extent this partition coefficient is related to oil-water and/or octanol-water partition coefficients. For example, it was well demonstrated that per component of which logP is lower than 8, the stability upon intravenous (IV) injection is questionable [42,138], The other two parameters are kQff, a kinetic parameter which describes the desorption rate of an emulsion component from the assembly, and kc, the rate of clearance of the emulsion from the site of administration. This approach is useful to decide if and what application a drug delivery system will have a chance to perform well [89],... 

Schuller [150] and Guillot [98] both observed that the copolymer compositions obtained from emulsion polymerization reactions did not agree with the Mayo Lewis equation, where the reactivity ratios were obtained from homogeneous polymerization experiments. They concluded that this is due to the fact that the copolymerization equation can be used only for the exact monomer concentrations at the site of polymerization. Therefore, Schuller defined new reactivity ratios, TI and T2, to account for the fact that the monomer concentrations in a latex particle are dependent on the monomer partition coefficients (fCj and K2) and the monomer-to-water ratio (xp) ... 

The octanol-water partition coefficient for surfactants can not be determined using the shake-flask or slow stirring method because of the formation of emulsions. In addition, the surfactant molecules will exist in the water phase almost exclusively as ions, whereas they will have to pair with a counter-ion in order to be dissolved in octanol. Therefore, experimental determination of K w does not characterize the partition of ionic surfactants (Tolls, 1998). On the other hand, it has been shown that the bioconcentration of anionic and non-ionic surfactants increases with increasing lipophilicity (Tolls, 1998). Tolls (1998) showed that for some surfactants, an estimated log Kow value using LOGKOW could represent the bioaccumulation potential however, for other surfactants some correction to the estimated log Kow value using the method of Roberts (1989) was required. These results illustrate that the quality of the relationship between log Kow estimates and bioconcentration depends on the class and specific type of surfactants involved. Therefore, the classification of the bioconcentration potential based on log Kow values should be used with caution. 

Flavor partition coefficients. The equilibrium distribution of a particular flavor molecule between two phases (e.g., oil-water, air-water, or air-oil) is characterized by an equilibrium partition function. These partition coefficients determine the distribution of the flavor molecules between the oil, water, and head space phases of an emulsion. 

During mastication, nonvolatile flavor molecules must move from within the food, through the saliva to the taste receptors on the tongue, and the inside of the mouth, whereas volatile flavor molecules must move from the food, through the saliva and into the gas phase, where they are carried to the aroma receptors in the nasal cavity. The two major factors that determine the rate at which these processes occur are the equilibrium partition coefficient (because this determines the initial flavor concentration gradients at the various boundaries) and the mass transfer coefficient (because this determines the speed at which the molecules move from one location to another). A variety of mathematical models have been developed to describe the release of flavor molecules from oil-in-water emulsions. 

One possibility is the entry of single radicals from the aqueous phase. The rate of entry of such radicals should depend on the concentration of the initiator in the water. This concentration is not so much determined by the solubility of the catalyst in water, as by its partition coefficient between hydrocarbon and aqueous phases. Although, for example, all the cumene hydroperoxide, in an amount usually employed in emulsion polymerization, easily dissolves in the aqueous phase, only a fraction of 1% of this amount is actually found in the water, the rest being dissolved in the monomer. The number of radicals formed in the water must therefore be very small indeed. 

Hibbott HW, Monks J. Preservation of emulsions— p-hydroxy-benzoic ester partition coefficient. J Soc Cosmet Chem 1961 12 2-10. 

Dmg release from emulsions is related to the partition coefficient of the dmg and the volume of the disperse phase, as well as to the concentration of surfactant which might solubilise the dmg in the aqueous phase. 

The amount of preservative remaining in the aqueous phase (C ) is related to the total amount (C) of preservative with a partition coefficient P in an emulsion with an oil/water phase ratio of O by equation (7.19) ... 

Usually, dmgs dissolved in oils are absorbed mainly via the aqueous phase. Transport from one phase to the other and partitioning are therefore important. In the absorption of drugs from o/w emulsions when the dmg partition coefficient is greater than 1, the amount of dmg in the aqueous phase (rather than the concentration) is a critical factor for absorption. In the absorption of poorly oil-soluble drugs, drug absorption from emulsions is greater than from aqueous solution. In an emulsion of volume ratio, O, the dmg concentration in the aqueous phase (C ) is related to the overall concentration of the dmg (C) by the expression ... 

Lipid emulsion formulations of prostaglandin Ej have been used in the treatment of vascular disorders. They exhibit a reduced incidence of side-effects at the site of injection, as does the diazepam lipid emulsion. A soybean emulsion stabilized by egg-yolk lecithin releases the PGEj over a period of 4-16 hours depending on pH (Fig. 7.24). The partition coefficients of PCEj between soybean emulsion and aqueous buffers at 20°C are shovm in Fig. 7.25, explaining why... 

For emulsion-type vehicles equations similar to those used to describe germicidal behaviour in two-phase systems can be applied. If Dj and D2 are the diffusion coefficients of the medicament in the continuous and disperse phases respectively, and 02 the volume fractions of these two phases, and P is the partition coefficient of the dmg between the... 

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