BIOTECHNOLOGY 7


and degraded, rendering the results unreliable.


As the solution ionicity increases, the situation deteriorates because even more current is required to drive measurable electrophoresis.


Existing products on the market notoriously ‘cook’ their protein samples and struggle to measure any macromolecule smaller than 5nm at a reasonable concentration.


Te key to the successful measurement of proteins’ mobilities lies in a much shortened measurement time and the availability of sufficient data to average away molecular diffusion.


New mobility instruments achieve these goals through massive parallelism of detection and extend the measurable molecular size range below 2nm (Fig. 1). A reduced measurement time (<60 seconds in most cases) contributes to excellent preservation of precious and fragile protein samples.


In a specific example, size exclusion chromatography (SEC) corroborated the preserved integrity of a sample of monoclonal antibody after the mobility measurement.


A sample recovery rate of >98 per


cent was obtained using Wyatt Technology’s Möbiuζ nobility instrument (Fig. 2). Another important advantage of recently developed mobility instruments which results from the patent- pending detection process is its much increased detection sensitivity: 2mg/mL lysozyme, or 0.5mg/mL BSA. Tis represents an order of magnitude greater sensitivity than the closest competitor.


With the new instrumentation, simultaneous measurement of the macromolecular hydrodynamic radius is available when combined with quasi-elastic light scattering, which utilises backward scattered light to determine the sample translational diffusion coefficient.


Both reusable flow-through cells and disposable cells can be employed for mobility (and QELS) measurements(stop-flow is required during mobility measurements).


Samples can be introduced by manual injection, an auto-sampler, syringe pump or an auto-titrator. Te Möbiuζ also has temperature control capability and is able to perform automated temperature studies.


Vincent Hsieh is R&D Scientist with Wyatt Technology, Santa Barbara, California, USA. www.wyatt.com


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Fig. 2. Measurement of protein electrophoretic mobility as a function of formulation pH. The pI value is determined as 9.1, in agreement with prediction based on its amino acid sequence.


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