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Static partition coefficient

Barrett and Thomas (10)proposed that these effects of differential monomer adsorption could be modeled by correcting homogeneous solution copolymerization reactivity ratios with the monomer s partition coefficient between the particles and the diluent. The partition coefficient is measured by static equilibrium experiments. Barrett s suggested equations are ... [Pg.274]

Poecilia reticulata, under static and semi-static conditions, quoted, Devillers et al. 1996) Sorption Partition Coefficient, log K ... [Pg.851]

In flavor analysis, the most frequent use of volatile traps is in analyzing the flavor compounds in foods using purge-and-trap or dynamic headspace, followed by GC-MS or GCO. Additionally, the traps can be used to measure static headspace and air-matrix partition coefficients where air is pushed out of an equilibrated cell containing the sample onto a volatile trap (Chaintreau et al., 1995). Volatile traps have been also used for flavor release measurements during eating (Linforth and Taylor, 1993) or simulated eating (Roberts and Acree, 1995). [Pg.1009]

Other advantages of LLC systems include the possibility to form reproducible, homogeneous stationary phases, a large sample capacity and a large contamination capacity (i.e. LLC columns are not easily polluted by contaminants in the mobile phase or the samples) [315]. Because the LLC system is generally well-defined, it allows a more rigorous theoretical treatment than other forms of LC. In particular, LLC retention data correlate well with liquid-liquid partition coefficients obtained from independent ( static ) experiments. [Pg.55]

The partition coefficients for these chelates have been determined by static methods and found to be as follows beryllium, 4.4 chromium, 16.1 ruthenium, 23.2 and cobalt, 33.5. [Pg.151]

In a static partition, the atom (necessarily radioactive in the present context) is distributed between two immiscible phases (liquid and/or solid). Since this procedure is sequential, the accuracy in the measurement of the average concentrations increases with the number of trials. For a given system, under given conditions, the determination of one partition coefficient (D) requires numerous repetitive experiments, even for the more simple case involving only one chemical species in each phase. The experimental conditions must always ensure that at the end of the experiment, the atom has reached permanent partition equilibrium between the two phases. Moreover, the short half-life of the nucleus does not bring any perturbation since there is only one alternative either the measurement indicates in which phase the atom is or the atom has disintegrated before the measurement and no information is obtained. [Pg.104]

Phase equilibrium measurements with supercritical SC-CO2 as solvent were performed with a variable volume static cell, Riha 1996. Isotherms and partition coefficients were determined for 13 oils. Each oil represents a separation product. [Pg.292]

There are different experimental methods for determining the gas-liquid partition coefficients leading to the determination of activity coefficients at infinite dilution y . The most frequently used methods are dynamic and static headspace methods. [Pg.418]

Most of the static headspace methods determine the partition coefficient by quantifying volatile concentration above a sample by gas-chromatography. The vapour phase calibration method (VPC) uses an external vapour standard for calibration. One must assure that the pure component is completely vaporized before injection. A widely employed alternative is the Liquid calibration static headspace (LC-SH) method (YoiWey et al. 1991 Nedjma 1997). A third approach uses HS-SPME. SPME may be used to determine partition coefficients if short sampling times are applied the process must only sample the headspace and not disrupt the equilibrium (Jung and Ebeler 2003). This method has become very popular to study the effect of wine macromolecules on the liquid-vapor equilibrium, (Whiton and Zoecklein 2000 Escalona et al. 2002 Hartmann et al. 2002 Aronson and Ebeler 2004). [Pg.419]

Some static headspace methods do not require an external calibration and are based on measurements performed at thermodynamic equilibrium between liquid and gas phase. In the phase ratio variation method (PRV) described by Ettre and Collaborators (1993), the partition coefficient calculation is based on the fact that the headspace concentration changes as a function of the phase volume ratio (gas and liquid phases), while the partition coefficient remains constant. This method has been recently applied to study the interactions between aroma compounds and macromolecules in different food systems (Savary et al. 2006, 2007) but so far not to the wine. [Pg.419]

Athes et al. (2004) compared the data from three static headspace methodologies (VPC, PRV and LC-SH) for determining gas/liquid partition coefficients of two aroma compounds in hydroalcoholic, multicomponent solutions at infinit dilution. They found that PRV was a simpler method compared to VPC and LC-SH and that VPC and PRV were more accurate than LC-SH since errors due to gas leaks and adsorption in gastight syringes are avoided. They suggested that these issues could be responsible for significant bias (50% lower values) obtained when using the LC-SH method. Nevertheless, all three methods were able to find an effect of ethanol (up to 20%) on the release of aroma compounds from their model system (Fig. 8F.1). [Pg.419]

Fig. 8F.1 Ethyl hexanoate (a) and isoamyl alcohol (b) partition coefficients [K (mol/mol)/(mol/mol)] at 25 °C in water, in 10 vol.% ethanol, and in 20 vol.% ethanol, with three static headspace methods PRV, VPC, and LC-SH (reprinted with permission from Athes et al. (2004) J Agile Food Chem 52 2021-2027. Copyright (2004) American Chemical Society)... Fig. 8F.1 Ethyl hexanoate (a) and isoamyl alcohol (b) partition coefficients [K (mol/mol)/(mol/mol)] at 25 °C in water, in 10 vol.% ethanol, and in 20 vol.% ethanol, with three static headspace methods PRV, VPC, and LC-SH (reprinted with permission from Athes et al. (2004) J Agile Food Chem 52 2021-2027. Copyright (2004) American Chemical Society)...
Shake-flask measurements are often employed to design a suitable LLPC system for a given sample mixture by assisting in the selection of the two phases in which the compound of interest shows a partition coefficient sufficiently different from those of the impurities. One of the two phases is then immobilized on a suitable support that is packed into the column, and the second phase is used as the mobile phase. In general, partition coefficients of solutes obtained from static experiments compare favorably with those obtained from chromatographic experiments [3]. A comprehensive thermodynamic treatment of LLPC can be found in Ref. 4, and the prediction and control of zone migration is discussed extensively in Ref. 5. [Pg.960]

When three dimensional particles were used instead of coatings, the diffusional and structural kinetics showed marked differences in the rates of mass to area in the concentration dependent regions of partition coefficient (lower temperature and mass sorbed). Thus, the fundamental assumption of the Kiselev Yashin equation that the mass/area ratio was equal for prepeak and peak regions was not met, and agreement with static data was fortuitous at best. [Pg.310]

Fig. 7.6 Options to assess imprinting effects and corresponding response factors, (a) Static mode assessment. (1) Template release. K = partitioning coefficient. (2) Comparison of template binding to a MIP with that to a NIP. IF = imprinting factor. (3) Comparison of binding of template with that of a close analog to the MIP. a = selectivity factor, (b) Flow through SPE mode assessment. Response factors can here be the % recovered template and for gradient elution, the cumulative recovery... Fig. 7.6 Options to assess imprinting effects and corresponding response factors, (a) Static mode assessment. (1) Template release. K = partitioning coefficient. (2) Comparison of template binding to a MIP with that to a NIP. IF = imprinting factor. (3) Comparison of binding of template with that of a close analog to the MIP. a = selectivity factor, (b) Flow through SPE mode assessment. Response factors can here be the % recovered template and for gradient elution, the cumulative recovery...
A number of test methods have been used to determine sink model parameters. The most common test protocol uses a dynamic, flow-through chamber and involves challenging a test sink material with a test gas [20, 31, 35, 36]. Details on this technique are presented later. Other methods include static tests and microbalance measurements. Borrazzo et al. [37 ] took a fundamental physical chemistry approach and used static equilibrium tests to determine partition coefficients for trichloroethylene and ethanol vapors and several types... [Pg.78]

Permeation-skin-gas chromatography (GC)/MS A silastic membrane was coated onto a fiber to be used as a permeation membrane. The MCF was immersed in the donor phase to partition the compounds into the membrane. At a given partition time, the MCF was transferred into a GC injector to evaporate the partitioned compounds for quantitative and qualitative analyses. This technique was developed and demonstrated to study the percutaneous permeation of a complex mixture consisting of 30 compounds. Each compound permeated into the membrane was identified and quantified with GC/MS. The standard deviation was less than 10% in 12 repeated permeation experiments. The partition coefficients and permeation rates in static and stirred donor solutions were obtained for each compound. The partition coefficients measured by this technique were well correlated (Pf — 0.93) with the reported octanol/water partition coefficients. This technique can be used to study the percutaneous permeation of chemical mixtures. No expensive radiolabeled chemicals were required. Each compound permeated into the membrane can be identified and quantified. The initial permeation rate and equilibrium time can be obtained for each compound, which could serve as characteristic parameters regarding the skin permeability of the compound. [Pg.192]

Gretsch C., Grandjean G., Haering M., Liardon R. and Westfall S. (1995) Determination of the partition coefficients of coffee volatiles using static headspace. 16th Int. Colloq. Chem Coffee (Kyoto, 9-14.4.1995) (ASIC, 1995), 1, 326-31. [Pg.360]

Table 6.6 [46] gives experimental results for the complexing constant together with values determined by other methods. In Table 6.7 [129] a comparison between chromatographic and static values of the partition coefficient is given for acetylene, methylacet-ylene and vinylacetylene, which form hydrogen bonds with various electron-donor stationary phases. The agreement between the GC and static values is reasonable. [Pg.202]

COMPARISON OF GAS CHROMATOGRAPHIC AND STATIC VALUES OF THE PARTITION COEFFICIENT, K, FOR UNSATURATED HYDROCARBONS IN VARIOUS SOLVENTS [129]... [Pg.204]


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See also in sourсe #XX -- [ Pg.29 , Pg.52 ]




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