ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 3, pp. 339!359. + Pleiades Publishing, Ltd., 2008.
Original Russian Text + A.G. Vitenberg, Yu.G. Dobryakov, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 3, pp. 353!373.
Gas-Chromatographic Determination of the Distribution Ratios
of Volatile Substances in Gas!Liquid Systems
A. G. Vitenberg and Yu. G. Dobryakov
Mendeleev All-Russian Research Institute of Metrology, Federal State Unitary Enterprise,
St. Petersburg, Russia
St. Petersburg State University, St. Petersburg, Russia
Received July 12, 2007
Abstract-Methods for determining the distribution ratios of volatile substances between liquid and gas
phases, based on gas3liquid chromatography or gas extraction in systems with constant or variable volume
under static or dynamic conditions, are classified and described, and their application fields are indicated.
The distribution ratio K, i.e., the ratio of the equi-
librium concentrations of a substance in the liquid
) and gas (c
is the most important characteristic of a heterogeneous
liquid3gas system. The quantity K is dimensionless,
but can be different for a given system depending on
the concentration scale chosen. In analytical measure-
are commonly expressed in mass
concentrations (mass in volume), because these units
considerably simplify the calculations, as data on the
molecular masses and densities of the gas and liquid
are not required. Furthermore, the distribution ratios
in the mass and molar concentration scales coincide.
Knowledge of the distribution ratios is necessary for
the development and optimization of many industrial
and laboratory chemical processes.
Formula (1) expresses the Nernst distribution law.
The quantity K is constant for ideal systems and
strongly diluted nonelectrolyte solutions to which the
Henry law is applicable. The distribution ratio gener-
ally depends on the solution composition. The area in
which the Henry law is obeyed (and K is constant)
depends on particular system. For example , for
solutions of lower alcohols in nonpolar solvents, the
upper limit of this area is on the level of 0.1 mol %.
Solutions of low-boiling hydrocarbons (n-pentane,
n-hexane) in high-boiling hydrocarbons (squalane)
obey the Henry law up to a concentration of ~1.5, and
systems of polar components (water3methanol), up to
a concentration of ~0.5 mol %.
In the case of dilute solutions, the distribution ratio
and its temperature dependence allow calculation of
the limiting activity coefficients of solutes g
are useful for the calculation of the thermodynamic
properties of dilute solutions, determination of the
parameters of molecular-statistics models for simulat-
ing phase equilibria in a wide range of conditions ,
estimation of the energy of solvation of solutes ,
and evaluation of intermolecular interactions in solu-
For solutions of limit dilution, the distribution ratio
can be calculated from physicochemcial constants of
the solvent and ith solute by the formula 
if the following quantities are known or can be meas-
ured: saturated vapor pressure p
and limiting activity
(symmetrical normalization) of the
solute, and the molecular weight M
and density d
the solvent. In formula (2), R is the universal gas
constant and T is temperature (K).
A powerful tool for determining the content of
volatiles in liquid and gaseous objects is gas-chroma-
tographic head-space analysis (HSA) . This
method is based on the principles of gas extraction
, i.e., on the distribution of a substance in the
liquid3gas system. Therefore, the key parameter deter-
mining the reliability of measurements of the content
of volatiles in liquid and gas media is the distribution