Size exclusion chromatograph instrumentation

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. 

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. 

This presentation demonstrates that a small minicomputer can be used to provide a full range of functions for collection and interactive reduction of data from a size-exclusion liquid chromatograph. A number of different users have collected in excess of 5000 chromatograms using this equipment. The experience gained with this system has influenced our approach to the automation of other analytical instruments. Careful attention to control paths, provision of "user friendly" access to the system functions, and careful management of the data archiving functions are crucial to the success of such efforts. 

In the first section, the mechanisms involved in size exclusion chromatography are discussed this is an area where additional understanding and clarification still are needed. Data treatment with respect to statistical reliability of the data along with corrections for instrumental broadening is still a valid concern. Instrumental advances in the automation of multiple detectors and the developm.ent of a pressure-programmed, controlled-flow supercritical fluid chromatograph are presented. 

For the purification of compounds, methods including molecular filtration, solid phase extraction (SPE, SPME), solvent extraction, and a variety of basic chromatographic techniques (thin layer, low pressure, ion exchange, size exclusion, etc.), HPLC, and GC (with derivatization of nonvolatile compounds) can be used. Additionally, instrumentation to identify compounds is available, such as the different spectrometric applications, including infrared (IR), mass (MS), ultraviolet and visible (UV-Vis), and NMR spectroscopy. In recent years, the so-called hyphenated techniques (combined chromatographic and spectral methods such as... 

Size-exclusion chromatography (SEQ and gel permeation chromatography (GPC) are very important tools in polymer characterization. They can provide the answers to key properties in polymer materials such as starches, cellulosics, nylon, polyethylene, PET, etc. GPC instruments are equipped with columns for aqueous or organic mobile phases. A refractive index detector is a very popular detector for most GPC applications. SEC (or GPC ) is used to chromatographically separate polymer molecules by size... 

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