Charge & Zeta Potential
Commonly associated with the stability of suspensions, zeta potential / molecular charge is also useful in assessing chemical modifications to biomolecules such as polysaccharides or IgG. In order to be relevant the charge must be measured in the solvent or formulation buffer of interest. That's why the Mobius® offers solutions for all solutions – volatile organics or highly conductive aqueous, as well as the more usual low-conductivity aqueous.
Both molecular charge and zeta potential are calculated from three primary measurements: electrophoretic mobility µ, hydrodynamic radius Rh and solvent conductivity σ. Light scattering determines electrophoretic mobility via Massively Parallel Phase Analysis Light Scattering (MP-PALS), and hydrodynamic radius via Dynamic Light Scattering (DLS). Only the Mobius plus integrated WyattQELS™ DLS module offers simultaneous measurement of µ and Rh. Conductivity is measured in the MP-PALS cell as well. Please see Electrophoretic Light Scattering Theory for more details.
MP-PALS utilizes low voltage and multiple low-noise, high-dynamic range detectors in parallel to achieve
the highest sensitivity without damaging fragile samples. Click to enlarge.
- Optimizing stability of colloidal solutions such as quantum dots, liposomes, and monoclonal antibodies
- Indication of chemical modifications that add or subtract charged residues (e.g., drug molecules in antibody-drug conjugates or super-sulfated heparin)
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Saito, S.; Hasegawa, J.; Kobayashi, N.; Tomitsuka, T.; Uchiyama, S.; Fukui, K. Effects of ionic strength and sugars on the aggregation propensity of monoclonal antibodies: influence of colloidal and conformational stabilities. Pharm. Res. 2013, 30, 1263-1280.
Instrumentation for Charge & Zeta Potential
Mobius™ - Massively Parallel Phase Analysis Light Scattering makes the Mobius the most sensitive electrophoretic light scattering detector available. Determines electrophoretic mobility, surface charge and zeta potential of fragile biomolecules as well as more robust nanoparticles, in native buffer. The Mobius is the only mobility detector to provide connectivity to an autosampler for hands off, multi-sample operation.
The Mobius incorporates dynamic light scattering (DLS) to provide simultaneous DLS measurements in the same scattering volume as PALS measurements. Hydrodynamic radius (Rh, determined by DLS) combines with electrophoretic mobility to calculate zeta potential and net charge.
DYNAMICS® - Software for electrophoretic and dynamic light scattering measurements in the Mobius. Calculates electrophoretic mobility, size and size distributions, and determines zeta potential, Debye-Hückel-Henry and effective charge. DYNAMICS also controls Agilent autosamplers and pumps for hands-off analyses of dozens of samples per day.
DYNAMICS is offered with a 21CFR(11)-compliant Security Pack option, enabling the use of the Mobius in a GMP environment.