ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 8, pp. 1244!1250. + Pleiades Publishing, Inc., 2006.
Original Russian Text + Yu.G. Dobryakov, A.G. Vitenberg, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 8, pp. 1259!1264.
OF SYSTEMS AND PROCESSES
Determination of Distribution Coefficients of Volatile
Sulfur-containing Compounds among Aqueous Solutions
and Gas Phase by Continuous Gas Extraction
Yu. G. Dobryakov and A. G. Vitenberg
St. Petersburg State University, St. Petersburg, Russia
Received March 1, 2006
Abstract-The method of continuous gas extraction at 10340oC was used to measure the distribution co-
efficients of hydrogen sulfide, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, and dimethyl disulfide
between the gas phase and buffer aqueous solutions with a constant pH value.
The problem of determining trace and microscopic
concentrations of volatile sulfur-containing substances:
hydrogen sulfide, alkyl mercaptans, sulfides, and di-
sulfides, in air, aqueous, and hydrocarbon media re-
mains topical because the existing methods, including
those officially accepted, fail to satisfy in the over-
whelming majority of cases the modern requirements
to sensitivity, selectivity, and accuracy of analysis.
A rather promising way to solve numerous problems
encountered in the development of techniques for
monitoring of volatile sulfur-containing impurities in
particular liquid or gaseous objects consists in use,
improvement, and development of the existing meth-
ods and procedures of gas-chromatographic vapor-
phase analysis (VPA) [1, 2]. This technique is based
on principles of gas extraction , i.e., on the dis-
tribution of a substance in the liquid3gas system.
Therefore, a key parameter determining the reliability
of data obtained in measurements of microscopic con-
centrations of volatile sulfur-containing substances is
the distribution coefficient, which is the ratio of
the equilibrium mass concentrations of a substance in
the liquid (c
) and gas (c
K = c
A group of the most important objects in which
the content of volatile sulfur-containing substance is
to be measured is constituted by aqueous solutions.
Microscopic concentrations of hydrogen sulfide, vol-
atile mercaptans, sulfides, and disulfides are to be
monitored not only in wastewater and natural water,
industrial discharges, and in the air of the working
zone at pulp-and-paper and petrochemical plants, but
also in various natural objects.
Data on the numerical values of the distribution
coefficients of hydrogen sulfide, methyl mercaptans
(MM), ethyl mercaptans (EM), dimethyl sulfide
(DMS), and dimethyl disulfide (DMDS) among water
or aqueous solutions of mineral substances and
the gas phase can be found in two reports [3, 4],
which, however, show strong discrepancies, as large
as several tens of percent for some components. These
discrepancies presumably result from use of different
variants of static VPA to measure K. The fundamental
difference between these variants consists in that dif-
ferent gas extraction procedures are employed. In ,
double extraction was used and the phase distribution
constant was calculated from relative areas under
peaks in chromatograms. In the later publication ,
a single-stage gas extraction was used and K was
calculated from the absolute values of the substance
concentrations in the liquid and gas phases.
The aim of this study was to refine the available
published data and obtain reliable information about
phase distribution constants among water or aqueous
solutions and the gas phase for volatile sulfur-contain-
ing substances of priority importance in sanitary-
chemical and ecological regards.
To improve the accuracy and eliminate the possible
systematic errors inherent in the static VPA (especial-
ly in analysis of the unstable mercaptans), the numer-