Field-Flow Fractionation
4
4.1
Fundamentals
The molar mass distribution (MMD) of complex polymers is typically analysed by
size exclusion chromatography (SEC). In the classical approach, the correlation
between the experimentally determined elution volume and the molar mass is done
using a set of well characterized calibration standards. For accurate results, the
chemical compositions and molar masses of the calibration standards must be
similar or close to the samples under investigation; see more details in Sect. 3.1.
SEC separates according to hydrodynamic size in solution and it is assumed that
one hydrodynamic size corresponds strictly to one molar mass. This, however, is
not always the case as has been shown, e.g., for high molar mass branched polymers
[1–7]. For such materials, co-elution of linear and branched molecules having
different molar masses has been observed [8]. Accordingly, SEC is not the best
tool for molar mass analysis in this case. Other problems associated with SEC relate
to unwanted polar or ionic interactions with the stationary phase that disturb the
SEC separation mechanism. Finally, samples with very high molar masses cause
problems in SEC because the largest molecules are frequently shear degraded by
the pores and frits of the columns, resulting in molar masses that are lower
compared to those of the injected sample [7, 9–14]. All of the above-mentioned
problems can lead to erroneous results and inaccurate interpretation of calculated
results.
Field-flow fractionation (FFF) is a chromatography-like technique, discovered
in the 1960s by J. Calvin Giddings, which has developed into a powerful alternative
fractionation technique for complex polymers. Most of the problems associated
with SEC can be overcome by FFF and additional information can be retrieved
using the various sub-techniques of FFF. The most popular FFF techniques are
asymmetric flow field-flow fractionation (AF4) and thermal field-flow fractionation
(ThF3). Studies have been carried out on natural and synthetic polymers using
organic and aqueous mobile phases, in various fields. Examples include the investigation of virus-like particles, starches and hyaluronic acid for aqueous
# Springer International Publishing Switzerland 2014
H. Pasch, M.I. Malik, Advanced Separation Techniques for Polyolefins, Springer
Laboratory, DOI 10.1007/978-3-319-08632-3_4
147
4
4.1
Fundamentals
The molar mass distribution (MMD) of complex polymers is typically analysed by
size exclusion chromatography (SEC). In the classical approach, the correlation
between the experimentally determined elution volume and the molar mass is done
using a set of well characterized calibration standards. For accurate results, the
chemical compositions and molar masses of the calibration standards must be
similar or close to the samples under investigation; see more details in Sect. 3.1.
SEC separates according to hydrodynamic size in solution and it is assumed that
one hydrodynamic size corresponds strictly to one molar mass. This, however, is
not always the case as has been shown, e.g., for high molar mass branched polymers
[1–7]. For such materials, co-elution of linear and branched molecules having
different molar masses has been observed [8]. Accordingly, SEC is not the best
tool for molar mass analysis in this case. Other problems associated with SEC relate
to unwanted polar or ionic interactions with the stationary phase that disturb the
SEC separation mechanism. Finally, samples with very high molar masses cause
problems in SEC because the largest molecules are frequently shear degraded by
the pores and frits of the columns, resulting in molar masses that are lower
compared to those of the injected sample [7, 9–14]. All of the above-mentioned
problems can lead to erroneous results and inaccurate interpretation of calculated
results.
Field-flow fractionation (FFF) is a chromatography-like technique, discovered
in the 1960s by J. Calvin Giddings, which has developed into a powerful alternative
fractionation technique for complex polymers. Most of the problems associated
with SEC can be overcome by FFF and additional information can be retrieved
using the various sub-techniques of FFF. The most popular FFF techniques are
asymmetric flow field-flow fractionation (AF4) and thermal field-flow fractionation
(ThF3). Studies have been carried out on natural and synthetic polymers using
organic and aqueous mobile phases, in various fields. Examples include the investigation of virus-like particles, starches and hyaluronic acid for aqueous
# Springer International Publishing Switzerland 2014
H. Pasch, M.I. Malik, Advanced Separation Techniques for Polyolefins, Springer
Laboratory, DOI 10.1007/978-3-319-08632-3_4
147