Page 61 - Illustrated Pocket Dictionary of Chromatography

56 DISK

R'
Surface Si O Si CH 2 CH 2 CH 2 OCH 2 CH(OH)CH 2 OH
R
Diol bonded phase

For further discussions of the R and R¢ groups, see octadecyl bonded
phase.

disk A solid-phase extraction format in which the packing material
(typically 3–7mm in diameter) is intercalated into a PTFE mesh.
Sample is drawn through the disk with an apparatus similar to a
solvent filtering unit.

displacement The process that best describes the retention
mechanism for liquid-solid (adsorption) chromatography.

distillation A method used to separate components of a liquid
through differences in their boiling points.
distribution The representation of the frequency with which indi-
vidual measurements yield different results is the distribution of the
data.

distribution coefficient, D (1) The chromatographic distribu-
tion coefficient (also called the partition coefficient), K D, is the ratio
of the equilibrium concentration of a species associated with the
stationary phase (C s) to that in the mobile phase (C m):

K D = C C m
s
(2) A more general solution distribution coefficient is used to describe
the stoichiometric ratios of a compound that partitions between two
definable and distinct phases. In liquid-liquid extractions the value of D
for a given species X partitioned between phases A and B is written as:
D = [] []
X B
X A
where B is typically the organic phase and A is the aqueous phase.
Also note that the distribution coefficient also takes into account
species that dissociate or associate. For example, a diprotic acid can