Concentration detectors size-exclusion chromatography

Size exclusion chromatography (SEC) separates molecules of a polymer sample on the basis of hydrodynamic volume. When the chromatograph is equipped only with a concentration-sensitive detector, i.e. conventional SEC, a molecular weight distribution (MWD) can be obtained from the chromatogram only through use of a calibration function relating molecular weight and elution volume V (2). 

A more sensitive viscometer than the drop-time glass capillary method is also needed in size exclusion chromatography (SEC) such as the gel permeation chromatographic (GPC) analysis of polymer molecular weight distribution (MWD). In an SEC system, a concentration detector is commonly used for providing the weight concentration profile of the polymer elution curve. 

The size exclusion chromatography for this study was done in the routine manner execept for the inclusion of an online viscosity detector called a Differential Viscometer <3> (Viscotek Corp., Porter, Texas, USAl. This instrument together with an RI concentration detector permits the calculation of intrinsic viscosities across the chromatogram. An IBM PC data system with software is also provided (5). The software acquires data from both detectors, and performs calculations of intrinsic viscosity and molecular weight distributions using the Universal Calibration Method. 

A low-angle laser light scattering (LALLS) detector was developed for use in size exclusion chromatography [133] and has been used coupled with FFF [134]. The advantage of this detector is that it can, in combination with a concentration detector (refractometer, UV/VIS, or IR photometric detector), provide direct data on molar masses of the eluted sample. 

Detectors capable of continuously measuring the density of the flowing liquid have been designed by Kratky et al. [146]. They are based on the measurement of frequency oscillations of a quartz tube through which the eluate flows. The oscillation frequency depends on the tube mass and, thus, for the given eluent, on the concentration and density of the solute. Their application to size exclusion chromatography has been described by Trathnigg and Jorde [147]. Kirkland applied such a detector for FFF [148]. 

The advent of size exclusion chromatography in the 1960 s provided an alternative to drying polymer-polymer-solvent samples to determine the equilibrium phase compositions. Size exclusion chromatography separates solvents from polymers and to a varying extent, polymers from polymers, based on the size of the molecules in solution. Ultraviolet spectrometry and refractive index detectors may be used to determine the concentrations of each of the polymers in each of the phases (Lloyd et al., 1980). 

Size Exclusion Chromatography. The molecular weight distribution of each sample was determined by size exclusion chromatography (SEC). A volume of 150 jxL of each sample at a concentration of 1-2 mg/mL was injected onto a set of four 30-cm PLgel (cross-linked polystyrene) columns (with porosities of 10 , 10 , 10, and 10 A) housed in a Waters 150C liquid chromatograph at 40 °C. The mobile phase was tetrahydrofuran, and the concentration detector was a differential refrac-tometer. 

Determination of the average chemical composition and polymer composition by size-exclusion chromatography (SEC) has been reported in the literature. Two different types of concentration detector or two different absorption wavelengths of an ultraviolet or an infrared detectors are employed the composition at each retention volume is calculated by measuring peak responses at the identical retention points of the two chromatograms. 

Size-exclusion chromatography is a liquid chromatography technique in which a polymer sample, dissolved in a solvent, is injected into a packed column (or a series of packed columns) and flows through the col-umn(s) and its concentration as a function of time is determined by a suitable detector. The column packing material differentiates SEC from other liquid chro-... 

Refractive index and specific refractive index increments - (k = dn/dc) of polymers in solution have been studied extensively in connection with light scattering measurements and size exclusion chromatography applications to polymer characterization for which refractometers are used as standard concentration detectors. Contrary to the observations made in the infrared region (12), refractive index increments have been shown to be a function of the molecular weight of the polymers (2) and, in some cases, of the copolymer composition (17). Therefore, the assumptions of linearity and additivity (Eq. 1 to 4) have to be verified for each particular polymer system. In the case of styrene/acrylonitrile copolymers, there is an additional uncertainty due to the... 

This technique is often used online in conjunction with size-exclusion chromatography. Since the signal from the light-scattering detector is directly proportional to the molecular mass of the protein times the concentration (mg mL ), by combining this signal with that from a concentration detector (refractive index or absorbance) it is possible to measine the molecular mass of each protein coming off the column. 

Size Exclusion Chromatography (SEC) is widely used technique polymer characterization. The standard configuration of a SEC apparatus consists of three parts (/-5), viz., a solvent-delivery system (equipped widi an injection port), the columns, and a differential refractive index (RI) detector. This basic configuration can be modified by adding an additional detector, either in series or in parallel to the RI detector (J-5). The second detector can be a viscometer (2), a concentration detector (3), an UV detector (4) or a Light Scattering (LS) device (5),... 

Figure 8 Concentration of materials in crude oils separated by size-exclusion chromatography. (A) Volume fraction eluted each second (B) moles eluted each second. 1, Arun crude oil 2, North Slope crude oil. (Reprinted with permission Yeung ES (1986) Detectors for Liquid Chromatography. New York Wiley John Wiley Sons, Inc.)...

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