Page 212 - Illustrated Pocket Dictionary of Chromatography

Z

Z-average molecular weight, M z Represents the second
moment of the weight distribution for a sample and is mathematically
represented as:

2
2
M z = ( w M 1 + w M 2 + ... + w M ) ( w M 1 + w M 2 + ... + w M )
2
1
2
i
2
1
i
i
i
2
= Â ( wM ) Â wM i
i
i
i
where w i represents the weight of each molecule, M i. This method is
very sensitive to changes in the high-molecular-weight region of the
sample. It is very susceptible to error when noise is present in the
system.
Z + 1-average molecular weight, M z+1 Represents the third
moment of the weight distribution for a sample and is mathematically
represented as:
2
2
2
3
3
M z 1+ = ( w M 1 + w M 2 + ... + w M ) ( w M 1 + w M 2 + ... + w M )
3
i
i
i
2
1
i
2
1
3
= Â ( wM ) Â wM i 2
i
i
i
where w i represents the weight of each molecule, M i. This method is
very sensitive to changes in the high-molecular-weight region of the
sample. It is very susceptible to error when noise is present in the
system.
zeolite A porous alkali-aluminum silicate that is used in specialized
separations.
zero dead volume (ZDV) Refers to union and fittings that are
machined in such a way as to minimize added extracolumn volume to
the system.
zeta potential, z The electrical potential established at the shear
plane/double layer interface of a system where an external voltage is
applied. In capillary electrophoresis the zeta potential represents
Illustrated Pocket Dictionary of Chromatography, by Paul C. Sadek.
ISBN 0-471-20021-2 Copyright © 2004 John Wiley & Sons, Inc.
217