Coupled Liquid Chromatographic Techniques in Molecular Characterization

Abstract

Complex polymers are distributed in more than one direction of molecular heterogeneity. In addition to the molar mass distribution (MMD), they are frequently distributed with respect to chemical composition, functionality, and molecular architecture (see Size‐exclusion Chromatography of Polymers). For the characterization of the different types of molecular heterogeneity it is necessary to use a wide range of analytical techniques. Preferably, these techniques should be selective towards a specific type of heterogeneity. The combination of two or more selective analytical techniques is assumed to yield multidimensional information on the molecular heterogeneity. The present review presents the fundamental ideas of combining liquid chromatography (LC) with other analytical techniques in multidimensional analysis schemes (see Size‐exclusion Chromatography of Polymers; Gas Chromatography in Analysis of Polymers and Rubbers; Field Flow Fractionation in Analysis of Polymers and Rubbers). The capabilities and limitations of different coupling techniques are discussed and a number of relevant applications are given. It is shown that multidimensional structural information can be obtained when different chromatographic techniques are combined. Another approach is the hyphenation of LC with information‐rich detectors. These detectors include molar mass‐sensitive detection systems, such as on‐line viscometry (VISC) and light scattering (LS). Information on the chemical composition of complex polymers can be obtained when spectroscopic techniques, like Fourier transform infrared (FTIR) (see Infrared Spectroscopy in Analysis of Polymer Structure–Property Relationships), nuclear magnetic resonance (NMR) or mass spectrometry (MS) are coupled to LC. The basics and applications of multidimensional LC are addressed rather extensively. A brief introduction to different separation mechanisms is given and the particular requirements for the first and second dimensions are discussed. In conclusion, state‐of‐the‐art examples for on‐line coupled two‐dimensional (2‐D) chromatography are demonstrated, and future developments are reviewed.

Size exclusion chromatography – A blessing and a curse of science and technology of synthetic polymers

“…The aim of SEC is to discriminate macromolecules of distinct sizes dissolved in appropriate solvent – not only to determine their molecular characteristics but also to remove undesired admixtures. There exist several monographs, chapters in books and review articles on this subject, for example 3–33. Most of them contain numerous quotations on articles devoted to theory, instrumentation, and applications of SEC.…”

“…This is the reason why the molar masses of complex polymers and complex polymer systems directly determined by SEC are only semi‐quantitative, reflecting the tendencies in changes of molecular characteristics of polymer sample but not the quantitative, absolute data. To obtain the quantitative molar mass values of complex polymers and complex polymer systems, the coupled and two(or multi‐) dimensional polymer HPLC techniques must be engaged 28–30, 32–34, 108, 116.…”

Characterization of branched polysaccharides using multiple‐detection size separation techniques

“…Multidimensional chromatographic separations offer in principle considerable potential for the separation of complex polysaccharides. Online coupling of interaction LC and SEC (LCxSEC) has been developed over the last few years for the separation of complex synthetic copolymers based on their size and chemical composition 106–110. The implementation of such 2‐D technologies could be of great utility for the high‐resolution separation of substituted polysaccharides or polysaccharide derivatives with different chemical substitution pattern.…”

Structure Determination of Polyacetals by Liquid Chromatography and Hyphenated Techniques

“…By applying 2D chromatography the resolution can in principle be greatly increased depending on the resolution of both dimensions. [37] The task of elucidating the correlation between molar mass distribution and end groups and/or Bufo content, respectively, calls for 2D experiments that combine GPEC and SEC, which are desirable. Typically, a 2D experiment is performed using a transfer loop.…”