The Turbiscan® Stability Index from Formulaction offers fast, robust, and objective quantifying of sample evolution over time in one single click.
Since its introduction, the TSI is fast becoming the main criteria used to compare sample stability evolution, and is now extensively used in research and development, quality control and academic research.
In this blog post, we look at the following:
- 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?
Using Formulaction’s vast experience (over 25 years) with stability and particle size characterization, and the knowledge of the static multiple light scattering (S-MLS) technology, it is possible to correlate the TSI value with a visual observation for better analysis of the TSI values and moving towards the stability prediction.
What is the TSI?
The Turbiscan® Stability Index is a dimensionless number gained by adding together all occurring destabilization phenomena in the sample that can be measured by noticeable change of the backscattering or transmission signal intensity along the sample height. These signal variations are directly linked to any destabilization in the sample, meaning that the higher the TSI value, the lower the stability.
How was the TSI scale developed?
Although the TSI provides a fast, efficient, and robust number for sample comparison, questions remain about the intensity of the destabilization and correlation with visual observation.
During Formulaction’s 25 years of experience in characterising liquid dispersions and colloidal systems, they have gathered a significant amount of stability measurement test results achieved with the Turbiscan that could be correlated with visual observation methods.
Their database contains thousands of samples of various types that their customers work with. These are both low and high concentrations, from nm to μm particle sizes, as well as emulsions and particle suspensions, and covers most of the application fields, including cosmetics, paint and coatings, food and beverages, dairy products, pharmaceutical injectable formulations, oil and lubricant emulsions.
From this large database, a TSI scale has been set to correlate a TSI number with destabilisation intensity and correlated to visual observation.
How does the TSI scale work?
While the TSI is a dimensionless number, it is a function of time. However, the time of calculation is not to be ignored when ranking samples. TSI values should be compared at the same aging time.
Once the TSI value, corresponding to a given state of destabilization, is calculated, the series of samples can be ranked and compared. The values are associated with a colour that allows for a direct analysis and sample validation, and can be seen below in the graph.
Where A+, A, B, C, and D correspond to the following key:
How can you adjust the TSI scale?
The Turbiscan LAB, Turbiscan TOWER and Turbiscan AGS are all equipped with the latest software version, where the TSI scale can also be represented as a bar chart.
The TSI scale colour code is displayed on the LCD screen of the Turbiscan TOWER.
Since the sample validation may vary from one sample type to another, it is possible to adjust border values of the scale in order to optimise the visual validation.
For example, in oil fields an emulsion may fail the stability requirements at TSI >10, while for a vaccine, maximum acceptable TSI may not exceed 2.5.
Therefore, in these cases it is possible to adjust the values for more specific analysis. The TSI scale is based on the TSI Global.
The Turbiscan scale combines its benefits, such as the detection of early-stage destabilisation, non-disruptive measurement, real stability measurement, and Formulaction’s 25-year experience in measuring stability.
It correlates the TSI value with visual observation to allow even easier comparison with previous methods and helps with defining stability criteria for stability comparison and stability prediction.
Turbiscan is a unique tool providing full characterization of your formulation with an extremely wide range of applications, including electronics, polymers, raw materials, pharmaceuticals, food and beverages, agrochemicals and paint and inks.
For more information on how the TSI can assist with your own research, development and/or production, please call us on: 01442 876777 for a free, no obligation quote, or email us at: firstname.lastname@example.org.
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