Page 140 - Illustrated Pocket Dictionary of Chromatography

140 OFFORD’S EQUATION

Offord’s equation Relates the electrophoretic mobility of mole-
cules, m em, to their net charge, Z, and their molar mass (g/mol):
ZM ]
m em = [ 32
on-column detection With on-column detection, the detector
is positioned such that the analyte is detected while it is within the
packed bed of the column. This typically requires the construction of
a special “window” along the column wall or insertion of a probe. The
advantage is that a considerable amount of band broadening can be
eliminated in this fashion.

optimization The process of changing operating parameters in s
system in order to fulfill all pre-established separation requirements
(e.g., run time, resolution, peak shape). Typical requirements for a
separation include one or more of the following: run time, resolution,
peak shape, sensitivity, selectivity, specificity, linearity and linear
range, precision and accuracy, ruggedness, robustness, etc.
overload An overload situation occurs when the concentration
of the analyte (of sample) exceeds the capacity of the column or the
linear range of the detector. Column overload refers to the condition
in which the concentration of the analyte exceeds the capacity of the
column precluding the rapid and reversible transfer of the analyte
from the mobile phase to the stationary phase. Peak shape is
adversely affected and often results in pronounced fronting. In a
detector, overload occurs when there is no further change in response
(detector output) for an increase in analyte concentration.

over-pressured layer chromatography (OPLC) A thin-layer
technique in which the sorbent layer is firmly pressed against a cover
membrane and solvent is forced through the sorbent layer. This tech-
nique is like HPC that the solvent is “pumped” through the sorbent,
but it is still planar chromatography. This technique has the advantage
over HPLC that viscous solvents can be used and over TLC that the
development of the chromatogram is faster.

oxidation The process by which a compound (or atom) loses an
electron.