Size exclusion chromatographic detector

A New Stand-Alone Capillary Viscometer Used as a Continuous Size Exclusion Chromatographic Detector... 

Yau, W.W.-, Abbot, S.D. Smith, G.A. Keating, M.Y. A new stand-alone capillary viscometer used as a continuous size exclusion chromatographic detector. ACS Symp. Ser. 1987, 352, 80. 

The automation of the SEC/Viscometer detector system is achieved by interfacing the DRI and viscosity detectors to a microcomputer for real time data acquisition. The raw data subsequently are transferred to a minicomputer (DEC PDP-11/44) for storage and data reduction. The automated data acquisition and analysis system for the size exclusion chromatograph with multiple detectors used in this study have been described previously.(23)... 

Experimental. The differential refractive indexes of polymer solutions were measured at 25°C with a Waters Scientific R-403 differential refractometer connected on-line with a size exclusion chromatograph. The refractometer was calibrated to refractive index units (Riu) with benzene/carbon tetrachloride solutions. The rationale behind using the refractometer on-line with the chromatograph is the elimination of impurities in the sample (water, residual monomer etc.) which affect the refractive index measurements particularly at low polymer concentrations and to calibrate the detectors at the flow conditions at which they were normally operated. Polymer solutions of several concentrations (0.015-0.0025 wt %) were injected repeatedly to verify the reproducibility of the measurements, which was typically An 0.5 x 10-6 for replicates on the same solutions. 

Experimental. Absorbances of selected polymer and copolymer samples were measured with a Waters 440 ultraviolet absorbence detector equipped with a 254 nm filter, and a Beckman 25 ultraviolet/visible spectrophotometer. The Water s instrument was used on-line with the size exclusion chromatograph (16). The Beckman 25 was used to calibrate and standardize the Water s 440 UV detector. THF was used as standard solvent. The extinction coefficients were estimated from absorbance measurements at several polymer concentrations. The standard deviation for the absorbance measurements was typically . 001 Au for replicates on the same sample. All measurements were done at room temperature. 

Figure 2.11 Schematic diagram of a gel permeation chromatograph (size exclusion chromatograph). The key elements are a pulseless pump, injection port, separation column containing appropriate crosslinked gel particles of controlled pore size, and one or more detector systems...

An analytical TREF system was first described by Wild and Ryle [8], Their system (Fig. 8) used components taken from a Waters model 200 size exclusion chromatograph. The solvent reservoir, degasser and pump from the Waters unit was used as was the refractive index detector system. In place of the SEC oven a temperature programmed oil bath provided the temperature gradients. A 0.2 g polymer sample was loaded in a hot trichlorobenzene solution into a small column packed with 40-60 mesh Chromosorb P. Crystallization was achieved by slow-cooling the polymer solution (0.2 g in 5 ml) in the packed column at a rate of 1.5 K/hour down to room temperature. The temperature rising elution was carried out at a flow rate of 6 ml/min and a rate of temperature rise of 8 K/hour. The refractive index response and the separation temperature were recorded continuously on a two-pen recorder. A calibration curve of methyl content vs. elution... 

Upnmoor and Brunner [7] evaluated a packed column SFC with a light scattering detector using a mobile phase of carbon dioxide modified with methanol for the chromatography of polymer additives. Moulder and co-workers [8] transferred eluent fractions from a packed capillary size exclusion chromatographic (SEC) column using a solvent vented interface to an open tubular CSFC column. The system was evaluated for the analysis of polymer additives. 

The most common detector is a differential refractometer, which then is proportional to the concentration of polymer at that elution volume. More-sophisticated detectors include a low-angle, light-scattering device that, in tandem with the differential refractometer, yields a direct measme of molecular weight associated with particles at the observed elution volume. Size-exclusion chromatographs are now highly engineered instruments that have proven invaluable to research on macromolecules. 

As mentioned in Chap. 1, randomly hyperbranched chains are even more complicated than dendrimers. It has not been completely clear whether they are fractal objects [11, 12] and whether those previously reported M-dependent intrinsic viscosities from an on-line combination of the size exclusion chromatograph (SEC) with viscosity and multi-angle laser light scattering (MALLS) detectors actually captured its structure-property relationship [11, 13]. In the next section, we ll discuss our experimental results in detail. 

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). 

Meehan, E. and O Donohue, S., Characterization of block copolymers using size exclusion chromatography with multiple detectors, in Chromatographic Characterization of Polymers, Hyphenated and Multidimensional Techniques, Provder, T., Barth, H. G., and Urban, M. W., Eds., American Chemical Society, Washington, D.C., 1995, chap. 18. 

Chromatographic approaches have been also used to separate nanoparticles from samples coupled to different detectors, such as ICP-MS, MS, DLS. The best known technique for size separation is size exclusion chromatography (SEC). A size exclusion column is packed with porous beads, as the stationary phase, which retain particles, depending on their size and shape. This method has been applied to the size characterization of quantum dots, single-walled carbon nanotubes, and polystyrene nanoparticles [168, 169]. Another approach is hydro-dynamic chromatography (HDC), which separates particles based on their hydro-dynamic radius. HDC has been connected to the most common UV-Vis detector for the size characterization of nanoparticles, colloidal suspensions, and biomolecules [170-172]. 

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