Page 142 - Illustrated Pocket Dictionary of Chromatography

142 PARTITION COEFFICIENT

this category. It should be noted that the retention mechanism for par-
tition chromatography is different from adsorption chromatography
in that adsorption chromatography is exclusively surface mediated
and partition chromatography models an analyte partially or com-
pletely entering the stationary phase. For partition-based separations
the C term in the van Deemter equation (mass transfer component)
is very important.

partition coefficient See distribution coefficient, D.

parts per billion, ppb A unit of concentration expressed as ng
9
analyte/g sample or g analyte/10 g sample, etc.
parts per million, ppm A unit of concentration expressed as mg
6
analyte/g sample or g analyte/10 g sample, etc.
pascal, Pa A unit of measure, in newtons/square meter, used for
backpressure displays in some chromatographic systems. 1MPa is
approximately 10atm or 150psi.

path length, b The distance that the source radiation travels
through the sample. Path length is an explicit variable in Beer’s law:
A =ebC. The direct impact is that absorbance is directly proportional
to path length.

peak area The total area under the peak elution profile, above the
baseline, and between the integration start and stop markers. See
integration.

peak broadening The result of all dispersion processes present
in the chromatographic system that increase the width of a peak
as it moves through the system. The extent of peak broadening is
2
represented as the sum of the variances (s ) of all independent
contributors:
2
2
2
2
2
s tot = s inj + s col + s det + s ct
2
2
where s tot is the total system variance, s inj is due to the injector,
2
2
2
s col is due to the column, s det is due to the detector, and s ct is due
to connecting tubing and unions.