Cross-fractionation chromatography

Figure 15. Cross fractionation by orthogonal chromatography arrangement of...

D. Recommendations. Cross-Fractionation using Orthogonal Chromatography has high potential in the analysis of complex polymers and even polymer latices (with Hydrodynamic Chromatography). Multi-detector analysis, particularly utilizing spectrofluorometry, should be very useful in developing the technique. 

Multi-dimensional Chromatography. Multi-dimensional chromatography is the term used to describe a variety of methods where fractions from one chromatographic system are each transferred to another for further separation. Combinations of SEC with thin-layer chrcmatography have been shown to enable separation of copolymers by composition in a "cross-fractionation". OC utilizes a combination of two SECs in a cross-fractionation approach. 

Fig. 30. Chromatographic cross-fractionation of300 mg poly(styrene-6-methyl methacrylate) with 47 wt % styrene. SEC curves of the fractions obtained by column adsorption chromatography. The large SEC curve is from the non-fractionated sample. (From Ref.1321 with permission)...

By the use of different modes of liquid chromatography it is possible to separate polymers selectively with respect to hydrodynamic volume (molar mass), chemical composition or functionality. Using these techniques and combining them with each other or with a selective detector, two-dimensional information on different aspects of molecular heterogeneity can be obtained. If, for example, two different chromatographic techniques are combined in a cross-fractionation mode, information on CCD and MMD can be obtained. Literally, the term chromatographic cross-fractionation refers to any combination of chromato-... 

Balke ST, Patel RD (1983) Orthogonal chromatography. Polymer cross-fractionation by coupled gel permeation chromatographs. In Craver CD (ed) Polymer characterization. Adv Chem Ser 203, American Chemical Society, Washington, DC... 

This book covers some of the significant advances in hyphenated chromatographic separation methods for polymer characterization. Chromatographic separation techniques in this volume include size-exclusion chromatography, liquid chromatography, and field flow fractionation methods that are used in conjunction with information-rich detectors such as molecular size-sensitive or compositional-sensitive detectors or coupled in cross-fractionation modes. 

CCC. A schematic diagram of the CCC system is shown in Figure 4 [this technique also has been named orthogonal chromatography 10-J3)]. Cross-fractionation on the polymer solution injected into the SEC column was performed on the solution passing through the switching valve in the time interval 830-850 s. This fraction was separated by isocratic elutions with column two. 

Polyolefins, other synthetic polymers, and water-soluble macromolecules have been investigated in highspeed SEC systems. High-speed SEC can be a major time saver in two-dimensional chromatography applications, which require about 10 hr analysis time for cross-fractionation. This can be reduced by a factor of 10, to about 1 hr, which makes it much more interesting for many laboratories. Details on these and additional highspeed applications can be found in Ref. [4]. 

Lee et al. (2005) proposed a method for analysis of flavonols in grape by performing berry extraction with acidified methanol (0.01% of 12 N HC1). After filtration, the solvent is removed under vacuum and the residue is dissolved in a 0.1 M citric acid buffer with pH 3.5. First, polyphenols are fractionated on a reverse-phase Ci8 cartridge (e.g., Sep-Pak 5g), then on a Sephadex LH-20 3-g cartridge (a cross-linked dextran-based stationary phase used for gel permeation, normal-phase partition, and adsorption chromatography). Four fractions finally are recovered by ethyl acetate and methanol, as shown in the f >w diagram Fig. 6.5. 

The method traditionally used for measuring the Bivariate Distribution is the "Chromatographic Cross Fractionation" (also referred to as "Two-dimensional Chromatography" or "Orthogonal Chromatography"). Macromolecules having different composition are separated in a silica column, and an SEC column is then used to elute chains having different sizes. ... 

Cross-fractionation chromatography, separating in a first step by composition followed by molar mass, is a very powerful approach to obtaining the full bivariate distribution of classical polyolefins and the most complete characterization of complex resins. TREF-GPC, TGIC-GPC, and SGIC2D are the various modes that can be used to obtain the three-dimensional analyses. Although not covered in this review, one should not forget the value of preparative fractionation combined with other separation techniques to obtain the three-dimensional plots as well as intramolecular characterization by spectroscopic techniques. 

Balke and Patel [62] used an orthogonal coupling of an SEC system to another HPLC system to achieve a desired cross-fractionation. They proposed to use it in an SEC/SEC mode, and suggested that a more descriptive general term for it is orthogonal chromatography . Both SEC systems utilized SEC columns. The solvent in the first system was chosen to accomplish only a hydrodynamic volume sreparation, and the solvent in the second system was chosen so as to be a thermodynamically poorer solvent for one of the monomer types in the copolymer in order to fractionate by composition under adsorption or partition modes as well as size exclusion. 

CED Cohesive energy density CEF Crystallization elution fractionation CFC Cross-fractionation chromatography CFT Continuum field theory CGC Constrained geometry catalyst CHX Cyclohexyl... 

Jeon, S.J. Schimpf, M.E. Cross-fractionation of copolymers using SEC and thermal field-flow fractionation for determination of molecular weight and composition. In Chromatography of Polymers Hyphenated and Midtidimensiorud Techniques, Provder, T., Ed. ACS Symposium Series No. 731, Ch ter 10 ACS Publications Washington, DC, 1999 141-161. 

Some workers nsed SEC for the first fractionation, and TLC [2,3] and high-performance precipitation liqnid chromatography [4, 5] were applied as the second chromatographic method. Balke and Patel [6,7] performed cross-fractionation by orthogonal chromatography (SEC-SEC) in which different mobile phases were used. Tanaka and co-workers [8] used the... 

Tref can also be combined with other fractionation techniques, such as size-exclusion chromatography (SEC) or successive solution fractionation (SSF). These cross-fractionation techniques can provide a great wealth of information on chain microstructme. The applications of cross-fractionation techniques using Tref will be summarized later in this review. 

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