Light scattering standard curve

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

The light scatter assay may be used to determine absolute numbers of viable cells if flow cytometry data from cell suspensions of known concentration are used to construct a standard curve. For that purpose, cell concentrations should be determined in a series of graded, standard cell suspensions with the use of a Coulter counter. A plot of those standard concentrations versus the number of events (Hght scatter signals) acquired during a specified acquisition interval in the flow cytometer may then be used to interpolate cell concentrations for test samples that have been assayed by the light scatter procedure. 

Molecular weightjmass detectors include light scattering detectors and viscosity detectors. When SEC is used in the characterisation of polymer systems, its main aim will be the production of a molecular mass/weight distribution and where possible absolute molecular weights. Mass calibration is a complicated matter (section 9.3.5.1) in that calibration curves differ for different polymer types, and for many commercial polymers, direct molar mass calibration is not possible because of the lack of suitable, known molecular weight standards. 

The molecular weight of the standards is supplied by the producers, either with a single value which should correspond to that of peak maximum, or with a complete characterization data sheet containing the values of and determined by osmometry and light scattering. In the latter case, the peak molecular weight to be inserted in the calibration plot is the mean value A typical calibration curve for a three-... 

SEC can be used as a measure of both the size and the MW dispersity of a polymer that is, it has the capability of finding the distribution of the sizes of polymer molecules. If standards of a known size are run previously, then a calibration curve can be created to determine the sizes of polymer molecules of interest in the solvent chosen for analysis often tetrahydrofuran (THE). Alternatively, techniques such as light scattering and/or viscometry, which do not rely on the calibration using standards of known MW, can be used online with SEC to yield absolute MWs. Because of the difference in size of two different polymers... 

Molecular absorption or light scatter can be corrected for by several methods. If the interfering salt composition is known, it may be possible simply to add the salt or salts to standards and make a direct comparison with calibration curves. It is relatively simple to measure the background absorbance. One way is to choose a nonresonance line from the lead hollow cathode lamp or another lamp that is not absorbed by lead and which occurs at least two bandpasses from the resonance... 

With a light-scattering detector, a log M versus elution volume calibration curve is constructed from a series of narrow molecular weight distribution polymer standards. A broad molecular weight distribution standard is then injected, and an iterative procedure finds the interdetector volume that superimposes the broad MWD standard calibration curve onto the one established by the narrow standards (38). 

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