Phase Ratio Variation Method Research Articles

Determination of Partitioning Coefficients of Numerous Organic Solutes between a Long-Chain Aliphatic Alcohol and the Gas Phase as a Function of Temperature

Partitioning coefficients of 44 organic solutes between hexadecan-1-ol and the gas phase at temperatures between 333.15 K and 383.15 K were determined with the phase ratio variation (PRV) method based on headspace gas chromatography. It was first established that the PRV method is suitable to determine partition coefficients using a solid matrix containing multiple solutes. Hexadecane/air partition coefficients for nonane and octan-1-ol measured using the PRV method agreed well with data from the literature. Homogeneous “solutions” of solid hexadecano-1-ol were prepared through melting, quick re-coagulation, and grinding. Exact phase ratios were determined by measuring mass and density. Comparison of partition coefficients determined using solutions containing either a single or multiple solutes showed that, in dilute solutions, the impact of the other solutes on the partitioning behavior can be neglected. Using very large phase ratios, the upper limit of partition coefficients that can be measured by the PRV method could be extended to approximately 20 000. The hexadecan-1-ol/air partition coefficients extrapolated to 298.15 K were well-correlated with both liquid-state vapor pressure and the octan-1-ol/air partition coefficient, suggesting that the partitioning behavior of most organic solutes in aliphatic alcohols can be estimated from their vapor pressure with a precision of approximately 1 order of magnitude simply by assuming that the activity coefficient is 1. The free energies, enthalpies, and entropies of hexadecan-1-ol/air phase transfer were derived from the measured data, and the phase transfer enthalpy was found to be correlated with the partition coefficient at 298.15 K.

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.

Quantitation of the Residual Solvent Naphtha in a Pharmaceutical Soft Gelatin Capsule Product by Equilibrium Headspace Gas Chromatography

An equilibrium headspace gas chromatographic (EHS-GC) method for the quantitation of the residual solvent naphtha in a pharmaceutical soft gelatin capsule product is described. The drug product, which is an encapsulated oil suspension, is exposed to the solvent naphtha during the manufacturing process. Headspace gas chromatography is the preferred method for the analysis of residual solvents in bulk pharmaceutical and drug products because the sample matrix is not introduced into the gas chromatographic system, resulting in a simpler and cleaner assay method. In EHS-GC sampling, the gas phase above the sample matrix is analyzed after it has reached thermal equilibrium. The EHS-GC method parameters are optimized by monitoring the n-octane gas-liquid partition coefficient of naphtha in the sample matrix via the EHS-GC phase ratio variation method of

Determination of gas-liquid partition coefficients by automatic equilibrium headspace-gas chromatography utilizing the phase ratio variation method

The new phase ratio variation method is described which represents a convenient way for the determination of gas-liquid partition coefficients for practical purposes, utilizing equilibrium headspace-gas chromatography (EHS-GC). This method is based on the relationship between reciprocal peak area and the phase ratio in the vial containing the sample solution; it involves regression analysis of the EHS-GC measurements of a number of sample vials containing the same sample solution but with a wide variation of phase ratios. Examples are given for both aqueous systems and systems consisting of a stationary (liquid) phase used as the solvent; comparison of the measured values with results obtained by other methods shows satisfactory agreement. A critical discussion of the conditions influencing the accuracy of the analytical results is given.