The Turbiscan Stability Index (TSI) is a Turbiscan specific parameter developed for formulators to compare and characterize the physical stability of various formulations with the ease of a single click and an output of a single, comparable, and replicable number.
It allows for the quantification of any type of destabilization, thanks to a one-click calculation representing a robust tool that is completely operator-independent.
The TSI Scale enables you to quantify and visualize the stability of different formulations, with values established based on the correlation with visual methods.
Considered as one of the key assets of the Turbiscan, the TSI provides the user with a robust and easy method for stability comparison and a global approach. Developed for R&D research and quality control, the TSI is also widely used in scientific publications by the academic community, making the TSI, the reference number for stability comparison and shelf-life measurement.
Quantifies any type of destabilization
A one-click calculation
Robust, and operator- independent
Dispersions are thermodynamically unstable and with time, complex formulations will evolve to reduce their energy to reach the lowest state, usually resulting in full and complete phase separation. Mechanisms to reach this low energy configuration are numerous and complex but can be classified in two categories:
Colloidal stability with particle size variation (such as aggregation, flocculation, coalescence, coagulation, or Ostwald ripening)
Macroscopic stability with particle migration (such as sedimentation, creaming, clarification, or phase separation)
Each phenomenon can be detect and quantified based on the Backscattering (BS) and/or Transmission (T) signal intensities measurements done by Turbiscan technology as both signals depend on particle concentration and particle size. Transmission and Backscattering intensities are recorded over the whole sample height and over time to get a complete insight of sample stability/instability.
For objective stability comparisons, global destabilization needs to be considered. This means comparing the amplitude of destabilization in the whole sample in a quantitative manner. This is the reason for the TSI calculation: to provide in a robust, objective, and global parameter in a single click that takes in account all destabilization reflecting the overall stability of a given sample.
The TSI calculation is based on an integrated algorithm that sums up the evolution of T or BS light at every position measured (h), based on a scan-to-scan difference, over total sample height (H):
The TSI corresponds to a cumulative sum of all the Backscattering or Transmission variation of the entire sample due to destabilisation. Therefore, the higher the TSI is the most unstable the sample is.
Once the TSI value is calculated, a series of samples can be ranked and compared easily, accurately and objectively. The values are associated with a color code that allows for direct analysis and sample validation, thanks to the TSI scale which links the TSI values to the corresponding visual observation.
Destabilization is detected but is at a very early stage (migration or size variation). In the A ranking, no visual destabilizations are observed at this stage.
TSI can be calculated and displayed at a given analysis time or over time as show below.