Chromatographic field flow fractionation

In conclusion one can say that SEC is a very powerful method for polymer characterization, especially in combination with other composition sensitive or absolute calibration methods. A big advantage is also that the sample amount is fairly small, typically 10 mg. For more complex polymers, such as polyelectrolytes, enthalpic effects often become dominant and also for rather high molecular weight polymers chromatographic methods such as field-flow fraction (FFF) techniques might be more suitable. For fast routine measurements linear columns are often used. 

In this chapter, we restrict our discussion to a chromatographic technique normally used for molecular weight measurements. The chromatographic concept can also be used for direct size (instead of molecular weights) measurement in the case of rigid particles, as we illustrate in our description of field-flow fractionation methods in Chapter 2. 

High-Speed Size Characterization of Chromatographic Silica by Flow/Hyperlayer Field-Flow Fractionation, S. K. Ratanathanawongs and J. C. Giddings, J. Chromatogr., 467, 341 (1989). 

Giddings JC, Kumar V, Williams PS, Myers MN (1990) Polymer separation by thermal field-flow fractionation high speed power programming. In Craver CD, Provder T (eds) Polymer characterization physical properties, spectroscopic, and chromatographic methods. American Chemical Society, Washington, DC, pp 1-21... 

Schimpf ME (1995) Determination of molecular weight and composition in copolymers using thermal field-flow fractionation combined with viscometry. In Provder T, Barth HG, Urban MW (eds) Chromatographic characterization of polymers hyphenated and multidimensional techniques. American Chemical Society, Washington, DC, pp 183-196... 

Ion Chromatography, edited by James G. Tarter 38. Chromatographic Theory and Basic Principles, edited by Jan Ake Jonsson 39. Field-Flow Fractionation Analysis of Macromolecules and Particles, Josef Janca 40. Chromatographic Chiral Separations, edited by Morris Zief and Laura J. Crane 41. Quantitative Analysis by Gas Chromatography, Second Edition, Revised and Expanded, Josef... 

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. 

Field-flow fractionation is a one-phase chromatographic system in which an external field or gradient replaces the stationary phase. The applied field can be of any type that interacts with the sample components and causes them to move perpendicular to the flow direction in the open channel. The most highly developed of the various FFF subtechniques is sedimenta-... 

E-3 Advantages of Field-Flow Fractionation over Chromatographic Methods... 

Field-flow fractionation appears to have several advantages over ordinary chromatographic methods for some applications. First, no packing material or stationary phase is needed for separation to occur. In some chromatographic systems, there may be undesirable interactions between the packing material or stationary phase and the sample constituents. Some solvents or sample materials adsorb or react with the stationary phase or its support. Macromolecules and particles are particularly prone to such adverse interactions. 

Particle-size and mass distribution curves, along with information on particle porosity, density, shape, and aggregation, can be obtained for submicrometer- and supramicrometer-size silica materials suspended in either aqueous or nonaqueous media by field-flow fractionation (FFF). Narrow fractions can readily be collected for confirmation or further characterization by microscopy and other means. Among the silicas examined were different types of colloidal microspheres, fumed silica, and various chromatographic supports. Size distribution curves for aqueous silica suspensions were obtained by both sedimentation FFF and flow FFF and for nonaqueous suspensions by thermal FFF. Populations of aggregates and oversized particles were isolated and identified in some samples. The capability of FFF to achieve the high-resolution fractionation of silica is confirmed by the collection of fractions and their examination by electron microscopy. 

A very recent volume edited by Berthed (2002) is on countercurrent chromatography - the support-free liquid stationary phase. Ebdon et al. (1987) review directly coupled liquid chromatogramphy-atomic spectroscopy. The review by Uden (1995) on element-specific chromatographic detection by atomic absorption, plasma atomic emission and plasma mass spectrometry covers the principles and applications of contemporary methods of element selective chromatographic detection utilizing AA, AES and MS. Flame and furnace are considered for GC and HPLC, while MIP emission is considered for GC and ICPAES for HPLC. Combinations of GC and HPLC with both MIPAES and ICPAES are covered and supercritical fluid chromatographic (SFC) and field flow fractionation (FFF) are also considered. 

In all of the many forms of chromatography, detection is an inherentiy important final step. The type of detection can aid in the analysis by gathering information that can be used to identify the peaks seen. There can be many peaks that elute from the column of a gas, hquid, or supercritical-fluid chromatograph. Certain detectors are in fact spectrometers that examine each peak for specific information on its identity. This chapter deals with this use of spectrometers as the tail-end detector in chromatography. Other separation techniques, such as field-flow fractionation or capillary electrophoresis, differ in their separation mechanisms, but as far as coupling to spectrometers behave like one of these three types of chromatography. 

It is discussed in more detail below. The most basic chromatographic technique is adsorption chromatography [82,83], in which separation arises from variation in the retention of the chain units or functional groups, due to their interaction with a stationary surface. Other techniques rely on rates of sedimentation [84,85], and diffusion-adsorption phenomena (thin layer chromatography [TT-C]) [86, 87]. Thermal diffusion is the basis for thermal field flow fractionation (TFFF) [88-91], discussed later. 

Ananieva, I.A. Minarik, M. Boutin, R. Shpigun, O.A. Janca, J. Characterization of chromatographic beads by micro-thermal field-flow fractionation. J. Liq. Chromatogr. Relat. Technol. 2004, 27, 2313. 

Regazzetti, A. Hoyos, M. Martin, M. Influence of operating parameters on the retention of chromatographic particles by thermal field-flow fractionation. Anal. Chem. 2004,... 

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