ζ_potential (DLS) and DSL particle size (nano range)
The technique is ideal for the measurement of the size of colloids, nanoparticles and molecules, without requiring agitation to make the sample suitable for analysis. From the size, an estimate of the molecular weight can be made, which has the benefit of being faster to confirm oligomeric state than size exclusion chromatography (SEC).
The Zetasizer Nano Z is dedicated to the measurement of zeta potential.
Zetasizer Nano Z features and benefits
• Measure samples up to 40%w/v
• Minimum sample volume of 20μL for zeta potential
• Measurement in high salt and non-aqueous media
• Wide range of sample suitability from nanoparticles to emulsions and macromolecules
• Automation using autotitrator to improve productivity
• Elimination of cross-contamination using disposable cells to improve accuracy
• Data assessment using quality report and ‘Expert advice’ system.
Measuring molecular size by DLS
The principle of dynamic light scattering is that fine particles and molecules that are in constant random thermal motion, called Brownian motion, diffuse at a speed related to their size, smaller particles diffusing faster than larger particles. The speed of Brownian motion is also determined by the temperature, therefore precision temperature control is essential for accurate size measurement. To measure the diffusion speed, the speckle pattern produced by illuminating the particles with a laser is observed. The scattering intensity at a specific angle will fluctuate with time, and this is detected using a sensitive avalanche photodiode detector (APD). The intensity changes are analysed with a digital autocorrelator which generates a correlation function. This curve can be analysed to give the size and the size distribution. To produce high quality data, the Zetasizer Nano series is designed to provide optimized components at every stage in the measurement chain from the laser and temperature control, through to the optical design and detector.
Focus on protein solutions
One of the key application areas for the Zetasizer is the characterization of proteins in solution.
• Molecular size and aggregation behaviour
• Molecular weight by DLS and SLS
• Second virial coefficient, A2, B22
• DLS interaction parameter, kD
• Protein charge and iso-electric point, PI
• Molecular conformation.