Handbook of Size Exclusion Chromatography and Related ...

useful information in the analysis of linear polyolefins at high temperature. They
also demonstrated, for the polymer studied, that no single detector was able to give
a complete picture of the MWD because of different sensitivity ranges. Jackson
and co-workers (218) showed that the Mark–Houwink exponent of polystyrene in
toluene could be measured with a relative standard deviation of less than 1% with a
single injection of a broad MWD standard.
As discussed earlier, a combination of a right-angle laser light-scattering
detector and a viscometer has proved to be a useful system for determining not
only molecular weight and intrinsic viscosity data but also radius of gyration of
linear polymers (11). Light-scattering measurements made at 908 simplify the
design of light-scattering instrumentation and, in principle, give a less noisy signal
by reducing spikes from particle contamination and stray light. In fact, a
commercially available HPLC fluorescence detector can be employed for these
measurements (212).
6 SUMMARY
The use of molecular weight sensitive detectors has increased dramatically the
information content that can be obtained from an SEC analysis. With these
detection systems, accurate measurements of fundamental molecular parameters,
both average and distributed values, can be determined readily. Furthermore, the
use of light-scattering detectors, and viscosity detectors for IVD, eliminates the
need for column calibration, which greatly increases the precision and reliability of
these measurements. However, as, in any other analytical instrumental procedure,
good chromatographic practise must be exercised: signal-to-noise ratio of detector
outputs must be maximized, defined polymer solutions injected, and instrument
calibration parameters and proper interdetector volumes established.
In addition to applications in the area of synthetic polymers, we foresee
exciting uses of molecular weight sensitive detectors for biopolymer characterization
and with interactive modes of separation, such as reversed-phase
gradient elution or ion-exchange chromatography. Finally, the combination of online
spectroscopic detectors, including UV-diode array, Fourier transform infrared,
mass spectrometry and possibly nuclear magnetic resonance with molecular
weight sensitive detectors represent a significant breakthrough for the
characterization of complex polymeric materials.
7 ACKNOWLEDGEMENTS
The authors gratefully acknowledge the valuable input and discussions with our
colleague Wallace W. Yau. We also thank the Corporate Center for Analytical
Sciences of the DuPont Company for giving us opportunity to prepare this chapter.
© 2004 by Marcel Dekker, Inc.