Partition Coefficients Of Volatile Compounds Research Articles

Determination of solid–liquid partition coefficient of volatile compounds by solid phase ratio variation based headspace analysis

A novel method has been developed for the determination of the solid–liquid partition coefficient of volatile analytes using headspace gas chromatography (HS–GC). The method is based on the headspace measurement for the three-phase equilibrium in sample vials containing different amounts of solid sample. Theory is presented that allows calculation of partition coefficient of the analyte from the HS–GC data obtained at the condition of solid phase ratio variation (SPRV). Analysis of errors demonstrates that this solid phase ratio variation method generates results with reasonable precision for all volatile compounds, much better than the liquid-focused (i.e., liquid phase ratio variation) method reported early.The solid phase ratio variation method was used to determine the solid–liquid partition coefficient of toluene in a water–polystyrene system, using polymer particles with average size ranging from 0.4 to 2.1μm. The results show that the partition coefficient of toluene in the given system is proportional to the specific surface area of the polymer particles, as expected.In summary, the method is a simple and practical tool for determining the solid–liquid partition coefficient of volatile analytes.

Effect of konjac glucomannan addition on aroma release in gels containing potato starch

The present study aimed to measure the retention of aroma compounds (ethyl acetate, ethyl hexanoate and carvacrol) in dispersions based on konjac glucomannan and/or potato starch, and to highlight the influence of konjac glucomannan on the mechanisms involved in aroma retention. Publications on the effect of konjac glucomannan on aroma release are scarce. Konjac glucomannan is a polysaccharide used as a food additive for its viscous and emulsifying properties. Retention of aroma compounds in dispersions was calculated from partition coefficients which were measured using the phase ratio variation method. This method, consisting of analyses of the headspace at equilibrium, enables the determination of the partition coefficient of volatile compounds in a gas/liquid system without external or internal calibration. The three aroma compounds chosen for this study behave differently toward amylose. Prior to the release study, the complexing behavior of carvacrol with starch, hitherto unknown, was investigated by X-ray diffraction: V6III amylose complexes were formed with carvacrol. Our results showed no specific interaction between ethyl hexanoate and potato starch or konjac glucomannan. Ethyl acetate retention seemed to be due to trapping in the complex network of polysaccharides and to the density of this network. Retention of carvacrol was influenced by the nature of polysaccharides present in the dispersion, and was mainly governed by specific interaction with starch. Additionally, the addition of konjac glucomannan to potato starch dispersions decreased the retention of volatile compounds complexing starch, but had little effect on the retention of the other aroma compounds.

Proposed alternative phase ratio variation method for the calculation of liquid–vapour partition coefficients of volatiles

The phase ratio variation PRV method is a classical way to determine the partition coefficients of volatile compounds between their solution and vapour phases in a variety of circumstances. However, some results obtained by this method can be disappointing. A new PRV equation in which the initial liquid-phase solute concentration is replaced by the liquid-phase solute concentration at equilibrium is proposed. This proposed PRV equation is a second-order polynomial equation. To thoroughly examine the possible modes of calculation, noisy dummy data were generated using both the classical, first-order PRV model (PRV1) and the proposed, second-order model (PRV2). Thus, pseudo-data obtained from simulations were compared to published experimental data. We observed that the second-order model, PRV2, produces a lower variability, allowing improved K precision. Moreover, the obtained K(PRV2) values are very close to those obtained by classical equilibrium headspace analysis (EHSA). The PRV2 model we propose responds to the demand for a simple, reliable method and is a useful alternative for the calculation of liquid–vapour partition coefficients.

Mixture of aroma compounds: Determination of partition coefficients in complex semi-solid matrices

The phase ratio variation method was used to determine partition coefficients of a mixture of aroma compounds in a complex model of fruit preparations containing starch and pectin or carrageenans as texture agents. This method enables easy determination of the partition coefficient of volatile compounds in a gas/matrix system without requiring any calibration. The present results were fully consistent with published data obtained with other methods. The influence of temperature on volatility as well as the effect of the composition and of the texture of the matrix were investigated. Under equilibrium an effect of polysaccharides was found only with hexanal, limonene, diacetyl and linalool. These were apparently trapped inside the matrix. Measurements on simplified systems suggested that retention was not due to interactions between aroma compounds and the gelling polysaccharide but rather to trapping in the complex network or to a combined effect of starch and of the gelling polysaccharide.

Partition coefficients of aroma compounds in polysaccharide solutions by the phase ratio variation method

The partition coefficients ( K) of aroma compounds (a homologous series of ketones, hexanal, t–2-hexenal, ethyl butanoate and 1-hexanol) in polysaccharide solutions were determined by the phase ratio variation method (PRV method) using a headspace autosampler. This method enabled easy determination of the partition coefficients of volatile compounds in a gas/liquid system without external or internal calibration, and the results agreed well with published data obtained by direct method. Measurements of K at different temperatures enabled the investigation of aroma compound retention by maltodextrin and β-cyclodextrin during heat treatment. In a maltodextrin solution, retention depended on the hydrophobicity of aroma compounds and it was favoured by the increase of temperature (from 60 to 80 °C). In a β-cyclodextrin solution, temperature variations produced different effects on the retention of aroma compounds and could reveal differences in the nature of the interaction with β-cyclodextrin.

Determination of partition coefficients by automatic equilibrium headspace gas chromatography by vapor phase calibration

Equilibrium headspace gas chromatography has been applied to the determination of the partition coefficients of volatile compounds in water-air systems. Only techniques that are suited to a fully automatic headspace procedure using the pneumatic headspace sampling-technique have been considered. Particularly simple is the technique of “vapor phase calibration —VPC” where an external vapor standard is used to calibrate the concentration of the volatile analyte in the headspace, while the concentration in the sample is found from the difference in the total amount in the vial. This technique is described in detail for 2-butanone in water. Finally, the water-air partition coefficients of several selected volatile compounds at different temperatures are listed together with their temperature functions.

A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems

Vejrosta, J., Novák, J. and Jönsson, J.Å., 1982. A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems. Fluid Phase Equilibria, 8: 25–35. A method has been developed for measuring the partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems, based on the direct analysis of both phases. A gas mixture containing a known proportion of a volatile compound is drawn through the liquid (water) until equilibrium is established. A defined volume of the liquid phase is then withdrawn through a porous-polymer trap while maintaining the system at equilibrium. The residual water in the trap is then expelled by a stream of nitrogen gas, and the deposit remaining is thermally desorbed and analyzed by gas chromatography. This approach, together with an experimental technique for producing gas mixtures containing an accurately known concentration of hydrocarbon at low values, makes it possible to determine accurately the partition coefficients of low-solubility compounds, such as for hydrocarbons in aqueous systems, at very low solute concentrations in the system. The method has been verified by measuring the partition coefficient of hexane between the gas and liquid phases of an aqueous system at various concentrations and temperatures.