ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 9, pp. 1538!1542. + Pleiades Publishing, Ltd., 2008.
Original Russian Text + L.S. Litvinova, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 9, pp. 1463!1468.
OF SYSTEMS AND PROCESSES
Determination of the Retention Characteristics in Thin-Layer
Chromatography Taking into Account the Actual Position
of the Mobile Phase Front
L. S. Litvinova
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received January 21, 2008
Abstract-To reveal the actual position of the mobile phase front, corresponding to the free volume of the
layer in thin-layer chromatography, it is suggested to use a nonsorbable low-molecular-weight marker.
The expressions for the capacity coefficient k', equilibrium coefficient K
, and corrected R
obtained taking into account the correction of the position of the mobile phase front.
One of the most important parameters of a chro-
matographic process is the capacity coefficient k':
are the amounts of a substance
in the stationary and mobile phases, respectively.
The capacity coefficient in thin-layer chromatog-
raphy (TLC)can be determined as follows :
are the residence times of a sub-
stance in the stationary and mobile phases, respec-
A characteristic feature of TLC is that the sum
t = t
is equal for all the substances being
separated, whereas in column chromatography all
the substances being separated have equal t
The retention in TLC is characterized by the rela-
is the distance passed by a substance from
the start and L is the distance passed by the mobile
phase front from the start (see figure).
Hence, the position of the mobile phase front is
the starting point in TLC. The velocity of the mobile
phase motion along the plate is also judged from the
front motion . If the mobile phase vaporization
from the wetted area of the sorbent layer and the
adsorption of the vapor on a dry sorbent layer are
excluded, then 
It follows from (2)and (4)that
Determination of one of basic characteristics of
a chromatographic process, k', by TLC is seemingly
easy. However, the necessary conditions for experi-
Schematic representation of TLC in a saturated chro-
matographic chamber: (1) start line, (2) chromatographic
spot of the sorbate (i), (3) mobile phase front found from
the position of the spot of a low-molecular-weight non-
sorbable (k' = 0) marker (M), and (4) observed mobile