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Zimm Plot/Second Virial Coefficient

Light scattering can be used to measure the second virial coefficient (A2) of a macromolecule. A2 is a measure of macromolecular self-interaction, and is a useful parameters for optimizing crystallization and formulation conditions of proteins.

Global fitting

Traditional Zimm plots involved multiple fits to multiple sets of data, and extrapolations to zero scattering angle and concentration. ASTRA employs a proprietary global fitting technology that upgrades the Zimm plot to a more robust, modern analysis. The global fitting technology removes all extrapolations from the Zimm plot method, helps identify inconsistent data sets, and provides more precise and robust results for A2. As with all analysis procedures in ASTRA, the global fit view (shown at right) offers immediate visual confirmation of fit quality using a new visual representation of the Zimm plot. Parameters can be changed in the grid view, and fit results viewed immediately.

Traditionally, A2 was measured using a painstaking process of preparing multiple concentrations of a sample, and then making multiple measurements to construct a classic Zimm plot. Wyatt Technology is committed to bringing this technology into the 21st century, particularly since it is of growing importance to the protein characterization community. Some of the avenues that we have implemented or are exploring include:

Online A2 determination

ASTRA supports the analysis of rapid injections of small volumes of a sample, ideally prepared in an autodilution process in an autosampler. This proprietary online analysis can retrieve A2 using a fraction of the sample needed for traditional measurements, and supports automation and high-throughput studies.



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Wyatt Technology is the recognized leader in light scattering instrumentation and software for determining the absolute molar mass, size, charge and interactions of macromolecules and nanoparticles in solution.

Wyatt's line of multi-angle static light scattering products couple to size exclusion chromatography (SEC-MALS), field-flow fractionation (FFF-MALS), and stop-flow composition-gradient systems (CG-MALS). Our dynamic light scattering (DLS) products operate in traditional cuvette as well as on-line and automated, high-throughput modes. We also offer unique instruments for electrophoretic light scattering (MP-PALS), differential refractometry, and differential viscosity.

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