ChromeGate 3.3.2 Software Manual - KNAUER Advanced Scientific ...

258 SEC Option
Universal Calibration
Universal calibration allows a narrow range polystyrene standard
calibration curve to be used to calibrate for a broader range of polymers.
Using the relationship between the hydrodynamic volume, (the product of
the Molecular Mass M and the intrinsic viscosity [�]) of the polymer and
its elution time), the narrow range calibration curve can be adjusted to
more closely fit the sample being analyzed.
The intrinsic viscosity [�] of a polymer is experimentally determined from
directly measuring the viscosity of the polymer solution. It is related to
the polymer Molecular Mass through the Mark-Houwink equation
[�]=Km a
where K and a are constants that vary with polymer type, solvent, and
temperature. Tables have been published that contain K and a constants
for a wide variety of polymers. Thus, using published values for K and a,
or the measured viscosity of the polymer, one can determine Molecular
Mass information for the sample.
Applications of SEC
SEC is used commonly for quality control of high Molecular Mass
polymers. Molecular Mass distribution is indicative of the physical
properties of the polymer. Such properties include strength, flexibility,
and tackiness, among others. Because the shape of the broad SEC
peaks can vary, in many cases simply examining the average Molecular
Mass number is not adequate to characterize the polymer, as two
polymers can have the same average Molecular Mass but very different
weight distribution. It is therefore important to evaluate a range of
different Molecular Mass calculations, as well as examine the actual peak
shape (overlay comparisons are helpful here) to get a good indication of
polymer quality.
The various different Molecular Mass numbers are used to characterize
different properties of polymers, as follows.
MN
MW
MZ
MV
Number-average Molecular Mass , is used in determination of
flexibility and tackiness of samples, which is a function of the
proportion of low-Molecular Mass material.
Weight-average Molecular Mass , is indicative of the strength of
the polymer, as it gives an indication of the proportion of high-
Molecular Mass material in the sample.
Z-average Molecular Mass , is used to determine brittleness,
and indicates the proportion of very high Molecular Mass
material in the sample.
Viscosity-average Molecular Mass , is used to relate the
average viscosity of the sample to its Molecular Mass .
MW/ MN Polydispersity, is an indication of how homogeneous the
sample is. A low number indicates more homogeneity, or
narrow Molecular Mass distributions. Higher numbers indicate
more complex polymers.
Using ChromGate ® SEC Software
The ChromGate ® Size Exclusion Software is an optional package that
enables ChromGate ® Chromatography Data System to perform SEC
calculations. Once the SEC option is enabled, it is possible for the user
to configure any one (or more) of the instruments connected to the
system as an SEC instrument. It is also possible to perform normal
partition chromatography calculations on some instruments, while
performing SEC on other instruments. (Note that SEC and partition