Page 209 - Illustrated Pocket Dictionary of Chromatography

W

water Molecular weight: 18.0; boiling point: 100°C; refractive index
(20°C): 1.3330; density (20°C): 0.998g/mL; viscosity (20°C): 1.00cP; UV
cutoff <190nm. Water is a major constituent in many reversed-phase
HPLC analyses. It is a deactivating material in normal phase separa-
tions (nonbonded phase). Water is available to meet many require-
ments (e.g., USP, ACS, pyrogenfree, etc), and so it is imperative that
the proper quality be used for the separation at hand.

weight-average molecular weight, M w The weighted average
mathematically represented as:
M w = ( w M 1 + w M 2 + ... + w M ) ( w 1 + w 2 + ... + w )
2
1
i
i
i
= Â ( wM ) Â w i
i
i
where w i represents the weight of each molecule, M i.
wide-bore gas chromatography columns Columns having
inner diameters of 0.53mm are classified as wide bore. Note that HPLC
columns typically do not have this classification.
Wilke–Change equation Used to calculate the diffusion coeffi-
cient of a solute A in solvent B, D AB (in cp):
D AB = [74 10 -8 (j B M B ) 12 T] [m B V A ] 0 6 .
¥
.
where j B is an associations factor for B, M B is the molecular weight
of B, T is the temperature (°K), m B is the solvent viscosity, and V A is
the molar volume of A at its boiling point.

window diagram A visual optimization technique in the resolu-
tion of multiple peaks that are affected by one operating parameter.
The operating parameter is changed in a precisely controlled fashion,
and the resulting resolution for each pair of analytes in the mixture is
plotted against the changed parameter. The point of intersection
having the highest mutual resolution is the optimal operating point.

Illustrated Pocket Dictionary of Chromatography, by Paul C. Sadek.
ISBN 0-471-20021-2 Copyright © 2004 John Wiley & Sons, Inc.
213