Zeta Potential Analysis with the Stabino
The Stabino® II is a second generation zeta potential instrument for analysing and optimising the stability of colloids and dispersions, based on measurement of streaming potential.
Employing a unique oscillating piston design, the system incorporates rapid pH and polyelectrolyte titrations for investigation of stable pH regions, Iso-Electric Point (IEP), charge density and surface functionalisation. The system is ideally suited to formulation development and has applications in quality control.
The heart of the Stabino is cylindrical PTFE measuring beaker and piston. Sample is added to the beaker and the piston oscillates at a constant frequency during measurement. Particles become immobilised on the surface of the beaker and piston, allowing the fluid stream created by the moving piston to shift the mobile ion cloud around each particle up and down, creating an oscillating frequency. The potential created is detected and measured by the two electrodes as streaming potential. From this, zeta potential is calculated.
Zeta potential alone is often not sufficient information to assess the stability of a colloid. +/-30mV is often quoted as a threshold for stability, but this does not give the full picture and is only relevant to the sample as it stands in that exact chemical environment. It is entirely possible for two samples to have -30mV zeta potential but have very different stabilities. The Stabino provides a full insight into the colloid being assessed, primarily via pH and polyelectrolyte titrations.
- pH titrations – allow the assessment of stable pH regions and determination of the iso-electric point (IEP) with extremely high resolution. IEP determination via classical light-scattering methods is problematic due particles agglomerating and then sedimenting out when approaching the IEP. The Stabino constantly mixes the sample via the oscillating piston and is therefore not hindered by this problem and can measure the exact pH at which zero charge is achieved.
- Polyelectrolyte titrations – by titrating a counter-charged polyelectrolyte solution, information on charge density can be estimated. This gives a much greater understanding of how stable a dispersion is. Predictions of shelf-life or stability over time can be built up using this method.
- Salt titrations – allow investigation of the relationship between conductivity and zeta potential Salt titrations are relevant to applications such as protein aggregation or waste water treatment, where changing the conductivity deliberately causes particles in solution to form aggregates so they can be filtered out of solution.
- Other titrations – ultimately, any titrant can use used on the Stabino and its effect on zeta potential monitored. Some custom applications may include assessing the effect of varying volumes of an additive or stabiliser, different amounts of pigment in an ink solution and so on.
The Stabino affords the user complete control over their experiments, giving extremely high resolution zeta potential plots thanks to the ability to titrate quickly and frequently, with potential readings taken every 5 seconds.
Interested in the Stabino®? Request a quote or call us on +44(0)1954 232 776 to discuss your requirements.