Molecular weight-sensitive detectors

Molecular-weight-sensitive detectors, such as a laser light-scattering photometer... 

Cheung, P., Balke, S. T., and Mourey, T. H., Data interpretation for coupled molecular-weight-sensitive detectors in SEC interdetector transport time,... 

The trend in modern SEC is to couple one or several other detectors (in particular molecular weight sensitive) to the concentration detector providing complementary... 

C. Jackson, H.G. Barth, Molecular weight sensitive detectors for size exclusion chromatography, in Handbook of Size Exclusion Chromatography and Related Techniques, vol. 91 (Chromatographic Sciences Series), C.-s. Wu, ed., Marcel Dekker, Inc., New York, 2004, p. 99. 

A polymer sample may consist of a mixture of species whose compositions differ enough to affect the responses of both the concentration-dependent detector and the molecular-weight-sensitive detector in a multidetector system. Examples are mixtures of different polymers or copolymers (Chapter 7) whose composition is not independent of molecular size. Conventional GPC cannot be used reliably to characterize such mixtures, but an on-line viscometer can be employed to measure molecular weight averages independent of any compositional variations [25]. Remember, of course, that such data characterize the mixture as a whole, and not just the major component. 

Jackson, C. Barth, H. G. In Molecular Weight Sensitive Detectors for Size Exclusion Chromatography Wu, C.-S., Ed. Dekker New York, 1995 Chapter 4, pp 103-145. 

The computer models described provide a functional simulation of SEC-viscometry-LS analysis of linear polymers. The results for the Flory-Schulz MWD are in qualitative agreement with previous results for the Wesslau MWD. Both models emphasize the importance of determining the correct volume offset between the concentration detector and molecular weight-sensitive detectors. For the Flory-Schulz model, the peak shape, as well as the peak elution volume, can provide information about molecular weight polydispersity. Future work will extend the model to incorporate peak skew and polymer branching. 

Two methods that determine the correct Mp values of the standards for molecular weight-sensitive detectors are discussed (3). These methods are based on transforming the MWD of the calibration standards into the responses of the molecular weight-sensitive detectors. The first... 

Significance of Peak Molecular Weight Corrections for Molecular Weight-Sensitive Detectors... 

Both the experimental and theoretical methods of determining the correct Mp values for the molecular weight-sensitive detectors give similar Mp values for calibration standards. This fact is apparent from Figure... 

Use of molecular-weight-sensitive detectors (e.g., differential viscometer or light-scattering detector) eliminates the need for calibration. With a differential viscometer used as a detector for thermal FFF, the intrinsic viscosity is first measured for each retention time and is then converted to molecular weight using the Mark-Houwink constants [5]. The use of accurate... 

GPC/SEC is a controlled separation technique in which molecules are separated on the basis of their hydrodynamic molecular volume or size [26], With proper column calibration or using molecular weight-sensitive detectors, such as light scattering, viscosimetry, or mass spectrometry, the MWD and the statistical molecular weight averages can be readily obtained. In their review, Barth et al. [26] mentioned that the GPC/SEC is the premier technique to evaluate these properties for both synthetic polymers and biopolymers. 

It is possible to add a second, molecular weight-sensitive detector to an SEC system to provide a direct means of absolute molecular weight calibration without the need to resort to external standards. These detectors represent refinements in classic techniques, such as light-scattering photometry, capillary viscometry (for intrinsic viscosity), and membrane osmometry for on-line molecular weight determination. Yau recently published a review of this subject with comparisons of the properties and benefits of the principal detectors currently in use (22). The present discussion is restricted to lightscattering and viscometry detectors because Yau s osmometry detector is not yet commercially available. The reader is referred to Chapter 4 for a comprehensive discussion of molecular weight-sensitive detectors. 

An alternative molecular weight-sensitive detector is the on-line viscometer. All current instrument designs depend upon the relationship between pressure drop across a capillary through which the polymer sample solution must flow and the viscosity of the solution. This relationship is based upon Poiseuille s law for laminar flow of incompressible fluids through capillaries ... 

Molecular Weight-Sensitive Detectors for Size Exclusion Chromatography... 

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