Viscosity detectors chromatography

Haney, M. A., The differential viscometer. II. On-line viscosity detector for size-exclusion chromatography, /. Appl. Polym. Sci., 30, 3037, 1985. 

A viscosity online detector in a size exclusion chromatography (SEC) instrument allows for a universal calibration for polymers with known K- and a-values. For polymers that are only soluble at high temperature, e.g., polyolefines, high-temperature detectors are available, which can be operated up to 200°C. In addition to molar mass measurements, viscosity detectors have also been employed successfully to obtain structural information of branched polymers [28]. 

Development of a Continuous Gel Permeation Chromatography Viscosity Detector... 

A continuous capillary viscosity detector has been developed for use in High Performance Gel Permeation Chromatography (HPGPC). This detector has been used in conjunction with a concentration detector (DRI) to provide information on the absolute molecular weight, Mark-Houwink parameters and bulk intrinsic viscosity of polymers down to a molecular weight of about 4000. The detector was tested and used with a Waters Associates Model 150 C ALC/GPC. The combined GPC/Viscometer instrumentation was automated by means of a micro/mini-computer system which permits data acquisition/reduction for each analysis. 

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. 

Gel permeation chromatography (GPC) is the established method for the determination of molar mass averages and the molar mass distributions of polymers. GPC retention is based on the separation of macromolecules in solution by molecular sizes and, therefore, requires a molar mass calibration to transform elution time or elution volume into molar mass information. This kind of calibration is typically performed with narrow molecular mass distribution polymer standards, universal, or broad calibration methods or molar-mass-sensitive detectors like light-scattering or viscosity detectors. 

A form of the viscosity detector has been used for exclusion chromatography, and prior experiments employing a single capillary have demonstrated the feasibility and usefulness of a continuous on-line viscosity detector in conjunction with a concentration detector (RI or UV). The sensitivity of the device, however, is rather poor, the minimum detectable concentration being about lO" g/ml. To date, the instrument has only been used in a recent application in polymer chromatograjdiy. 

Figure 13 Schematic representation of (a) the four-capillary viscosity detector (reprinted from Pasch, H. Trathnigg, B. HPLC of Polymers, Springer Berlin-Heidelberg-New York, 1998 with kind permission of Springer Science+Business Media) and (b) universal calibration cunte (reprinted from Mori, S. Barth, H. G. Size Exclusion Chromatography, Springer Berlin-Heidelberg-New York, 1999, with kind permission of Springer Science+Business Media).

Advances in size-exclusion chromatography, coupled with refractive index, absorption, viscosity, and lightscattering detectors, and MALDI-ToFMS, have made it possible to accurately determine molecular weight distribution (oligomer profiling), even at the relatively low values of polymeric additives (up to about 5000 Da). Advances in column design, e.g. high-resolution PS/DVB columns (> 105 plates m-1) mean that SEC can provide a valuable alternative to conventional HPLC techniques for the separation of small molecules. 

The conformational mobility of a chromophoric main-chain polymer is often connected to its electronic structure. Therefore, changes in the UV-visible absorption spectra and/or chiroptical properties are spectroscopically observable as thermo-, solvato-, piezo-, or electrochromisms. It is widely reported that o-conjugating polysilanes exhibit these phenomena remarkably clearly.34 However, their structural origins were controversial until recently, since limited information was available on the correlation between the conformational properties of the main chain, electronic state, and (chir)optical characteristics. In 1996, we reported that in various polysilanes in tetrahydrofuran (THF) at 30°C, the main-chain peak intensity per silicon repeat unit, e (Si repeat unit)-1 dm3 cm-1, increases exponentially as the viscosity index, a, increases.41 Although conventional viscometric measurements often requires a wide range of low-dispersity molecular-weight polymer samples, a size exclusion chromatography (SEC) machine equipped with a viscometric detector can afford... 

Alkali cellulose, 4 716 Alkali earth metal nitrides, 17 206-207 Alkali flame-ionization detector (AFID), gas chromatography, 6 381 Alkali-gravity-viscosity (AGV) charts, for silicate glasses, 22 462, 463 Alkali halide disk method, 14 229 Alkali-immobile compounds, dye release from, 19 288... 

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