Turbiscan Stability Index

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. 
NEW:  The recently introduced TSI Scale enables to quantify and visualize the stability of different formulations, with values established based on the correlation with visual methods. 

The TSI can be used over the whole formulation’s life cycle, from research and development to quality control : 

-       Research and Development: select the best formulation among the different test preparations with varying raw material, active ingredient concentration, surfactants or other stabilizers amount…

-       Reformulation: update an existing formulation to meet new specifications or regulatory rules and check the impact on the stability.

-       Process scale-up: adjust process parameters for the industrial scale and ensure similar stability at every development step

-       Quality Control: check production batch compared to the required stability specification

TSI is also more and more used in the academic field with more than 500+ publications using the TSI to study and compare the stability of suspensions, emulsions, and foams.
Considered as one of the biggest advantages of the Turbiscan, the TSI provides the user with a robust and easy method for stability comparison and a global approach. 

Key Benefits

  • Quantifies any type of destabilization
  • A one-click calculation
  • Robust, and operator-independent

How does it work?

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, complex and can be classified in two categories:

-       Colloidal stability with particle size variation such as aggregation, flocculation, coalescence, coagulation, Ostwald ripening…

-       Physical stability with particle migration such as sedimentation, creaming, clarification, phase separation…

The destabilization can occur from a couple of seconds up to many years for the most stable formulations, sometimes it can take some time before the occurring change becomes visible, thus using the Turbiscan technology and its high sensitivity can help to predict stability as it will detect the destabilization up to 200 times faster than naked eye and permits the user to save precious time

Each phenomenon can be detected and quantified based on BackScattering and/or Transmission signal intensities with extreme ease thanks to the Turbisoft. 

For the objective stability comparison, the 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 single click a robust, objective and global parameter that takes in account ALL the destabilization reflecting the overall stability of a given sample 

Any destabilization phenomenon happening will have an impact on the BackScattering and/or Transmission signal intensities during the aging process. The formulation with the highest intensity variation is the one to change in the most significant way, thus the least stable.

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):

In another way, TSI corresponds to a cumulative sum of all the BackScattering or Transmission variation of the entire sample

As the scans add up over time the TSI value can change, at a given time a single TSI value is associated and the “Destabilization kinetics” graph can be created showing TSI evolution over time. 

Below a representative example on 6 samples: 5 new formulations (A, B, C, D, and E) were compared to the standard formulation (a known stable formulation such as existing product, benchmark…)

Variations are detected at the earliest stage, observed days before the changes appear to the naked eye

In this case, samples present different destabilization profiles, from creaming and sedimentation to size variation. Deciding on the stability based simply on the raw data requires kinetic calculations based on different types of variations ( migration, size...). The TSI calculation can provide the overall stability kinetic in a single click and display this information as a function of time in a very simple graph. All the measurements are overlaid for easy comparison and straight forward decision making of the best formulas regarding stability. 

Here, is its simple to observe Sample D is the least stable, Sample C and A show stability lower than reference product, whereas sample B and E offer similar and excellent stability compare to the reference sample.

Questions that remain when using the TSI are: How significant is the TSI value? Which value allows to consider the sample stable? How much different are the samples in terms of global physical stability? How to link the TSI values with the visual ranking? …

Once the TSI value, corresponding to a given state of destabilization at time t, is calculated, the series of samples can be ranked and compared. The values are associated with a color that allows for direct analysis and sample validation thanks to the TSI scale which links the TSI values to visual observation corresponding.

A+ Visually Excellent

No significant destabilization is observed with the Turbiscan® and the sample remains visually stable. A+ ranking is the best stability mark.

A Visually Good

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. 

B Visual Pass

The variations detected by the Turbiscan® are higher than the “early” stage and correspond to the beginning of the destabilization, however, the destabilizations remain non-visual in most cases (>90%).

C Visual Warning

Important stability destabilization corresponding to large sedimentation/ creaming, wide particle size variation, small phase separation... The destabilization may or may not be visible at this stage and the sample in the C ranking sample must be carefully monitored. 

DVisual Fail

Extreme and important variation and the destabilization most likely visible corresponding to large sedimentation or creaming, phase separation, wide change in the particle size or color…

> Considers any type of destabilization

Coalescence, flocculation, sedimentation, phase separation… Don't miss any phenomenon taking place in your sample, the algorithm takes any change into account!

> Fully automated

Compute the TSI for all your samples in just one-click after the data acquisition. Rank your samples from the least to most stable automatically. Click - Compare - Decide

> Robust and operator-independent

No parameter needed, no settings by the operator required. If the TSI increases, it's only because of the product changes.