On-line gel permeation

On-line determination of molar mass (MM) and molar mass distribution (MMD) has become possible with the introduction of an on-line gel permeation chromatograph. Such an instrument does automatic sampling, dilution, injection, elution, detection and analysis, much like an on-line gas chromatograph. Deconvolution is automatic, as is calibration from a mixture of standards. As with all on-line chromatographic techniques, maintenance and reliability are a problem f - large-scale production use. 

Not all process variables are measurable on-line most end-use properties are not. Some controlled variables affecting product quality are measurable or they can be estimated many are not. Even when the technology to measure these variables on-line exists, the cost of such sensors may be prohibitive. On-line gel permeation chromatography for the determination of MWD is an example. Almost all controlled variables specifying operating conditions are measured. Most manipulated variables are known because they are either measured or set by a control system (or both). As discussed above, disturbances may be measured or unmeasured. 

Yamamoto et al. also coupled gel permeation HPLC and CE in an on-line fashion in 1990, where capillary isotachophoresis was again used in the second dimension. This technique was also not comprehensive due to the loss of resolution between the techniques. It was also not particularly fast, with a 23 min CE cycle, which was repeated 90 times throughout the HPLC run (14). Volume incompatibility between HPLC and CE was one problem not addressed in this study, in which a large HPLC column was coupled to an electrophoresis capillary. 

Gel permeation ehromatography (GPC)/normal-phase HPLC was used by Brown-Thomas et al. (35) to determine fat-soluble vitamins in standard referenee material (SRM) samples of a fortified eoeonut oil (SRM 1563) and a eod liver oil (SRM 1588). The on-line GPC/normal-phase proeedure eliminated the long and laborious extraetion proeedure of isolating vitamins from the oil matrix. In faet, the GPC step permits the elimination of the lipid materials prior to the HPLC analysis. The HPLC eolumns used for the vitamin determinations were a 10 p.m polystyrene/divinylbenzene gel eolumn and a semipreparative aminoeyano eolumn, with hexane, methylene ehloride and methyl tert-butyl ether being employed as solvent. 

A high pressure gel permeation chromatograph (GPC) has been used to monitor the performance of the reactor. A novel aspect of the GPC is that, it too, has been put on-line to the process control computer and both data collection and analysis have been made automatic while giving the operator full interactive facilities. 

Pille and Solomon investigated the formation of the above mentioned microgels using gel-permeation chromatography with an on-line light scattering detector [249]. They showed that the primary particles appear very early in the reaction and microgels are formed by interparticular reactions of the primary particles. 

SPE, chromatography (i.e., thin-layer chromatography, gel-permeation chromatography and HPLC) and on-line multi-dimensional chromatography. These techniques are rarely used in routine tablet assays due to their technical difficnlties, labor intensity and problems with recovery. 

Experimental Techniques. Chromatography was performed on a Varian model 5060 HPLC equipped with a RI-3 refractive index detector. A Vista Plus Gel Permeation Chromatography (GPC) data system was used consisting of a Vista 401 chromatography data system serially connected to an Apple II microcomputer. The Vista 401 performs data acquisition and allows data storage and automations capability while all SEC data processing is performed on the Apple II by means of user-interactive GPC software for automated, on-line calibration and polymer analysis. 

Current practices in analytical SFE are organized into off-line and on-line procedures, despite their common physicochemical basis. Off-line SFE, the current method in fashion, offers more flexibility with respect to extracting different sample sizes and types, as well as in the choice of the final analytical method. On-line procedures are usually combinations of SFE with ancillary techniques such as GC, LC, supercritical fluid, or gel permeation chromatography. 

Acetate buffer extn, heat deprtn, on-line cleanup on Progel-TSK gel-permeation column, trace enrichment on PLRP-S, 15-25... 

Figure 3. Gel permeation data for linear randomly coiled polypeptides on various agarose resins, plotted according to the method of Ackers (9). M0 555 is plotted vs. the inverse error function complement of Kd (erfc 1 Kd). Lines drawn through the data points represent best fits obtained from linear least-squares analysis of the data. Numerical designation of each curve represents the percent agarose composition for the resin used. Filled triangles on the curve for the 6% resin, and the filled squares on the curve for the 10% resin are points determined using fluorescent proteins. Data for the labeled polypeptides were not included in the least-squares analysis.

The static laser light scattering apparatus used as an on-line GPC detector has been popular for a while. Here, we illustrate another but less known method of combining the results from (gel permeation chromatography) and DLS. The basic principle is as follows There is a similarity between these two tools in that the translational diffusion coefficient D obtained by DLS and the elution volume V in GPC are related to the hydrodynamic size of a given macromolecule. In a first approximation, if the hydrodynamic size is proportional to the molar mass, we have... 

It consists in developing numerical and analytical methods to invert a linear viscoelastic material fimction to determine the molecular weight distribution. There are several reasons to pursue such an objective many commercial polymers are slightly or not at aU soluble in usual solvents, thus techniques like gel permeation chromatography or light scattering are inapplicable. Rheological characterization can be performed on-line and in real time and it is also a less cots-effective technique. 

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