TURBISCAN Stability Index (TSI)

The TSI is a Turbiscan-specific parameter designed for formulators to compare and characterize the physical stability of various formulations with a single click and a single, comparable and reproducible number. It enables the quantification of any type of destabilization, thanks to a one-click calculation that is a robust and completely user-independent tool.

Considered one of the key benefits of the TURBISCAN, this index provides users with a robust and easy method for stability comparison and a global approach. The TURBISCAN Stability Index was developed for R&D research and quality control and is also widely used in scientific publications by the academic community. All these applications make this index the reference parameter for stability comparisons and durability measurements.

Dispersions are thermodynamically unstable, and over time complex formulations evolve to reduce their energy and reach the lowest state, usually leading to complete phase separation. The mechanisms for achieving this low-energy configuration are numerous and complex, but can be divided into 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 detected and quantified based on the backscatter (BS) and / or transmission (T) signal intensities measured with TURBISCAN technology, as both signals depend on particle concentration and particle size, utilizing Static Multiple Light Scattering (SMLS). The transmission and backscattering intensities are recorded over the entire sample height and over time to gain full insight into the stability / instability of the sample.

For objective stability comparisons, the global destabilization must be taken into account. This means that the amplitude of the destabilization in the entire sample must be compared quantitatively. This is the reason for the TSI calculation: to provide a robust, objective and global parameter with a single click that takes into account the whole destabilization and reflects the overall stability of a given sample.

The TSI calculation is based on an integrated algorithm that sums up the evolution of the T or BS light at each measured position (h), based on a scan-to-scan difference over the entire sample height (H):

Once the value of the index is calculated, a series of samples can be graded and compared easily, accurately and objectively. The values are assigned to a color code that allows direct analysis and sample validation thanks to the TSI scale that links the values to the corresponding visual observation.

 Destabilization is detected, but is at a very early stage (migration or size change). In the A ranking, no visual destabilization is observed at this stage. The Turbiscan Stability Index can be calculated and displayed at a given analysis time or over time as shown below.