Optical Measurement of Stability and Particle Size by Static Multiple Light Scattering - Turbiscan®

In formulation studies of suspensions, emulsions, and foams, analysis of colloidal stability and determining shelf life are the important criteria. TURBISCAN® is the first patented technology to investigate destabilization mechanism in concentrated dispersed media, thereby being the only technology to enable accelerated aging tests on the original unstressed products.

Sedimentation, creaming, coalescence, aggregation, and agglomeration of even highly concentrated formulations can be detected, at a very early stage, without stress or dilution. Stability kinetics analysis is enabled for a reliable and efficient analysis of samples, and for the assessment of the overall quality of formulations, a Turbiscan stability Index can be calculated, thereby enabling quantification of the destabilization with a single number.

TURBISCAN Technology Explained

Static multiple light scattering (SMLS) is the only stability analysis method to provide the benefit of working in concentrated media: It is best suited for working without stress and without dilution over an extensive range of particle size (10 nm to 1 mm) at higher concentrations (of up to 95% v:v).

A major portion of the emitted light is scattered by the particles in the sample and only a partial amount passes through the tube. TURBISCAN® has the ability to detect the intensity of not just the transmitted light but also the backscattered light, over the entire tube height. These intensities enable local physical heterogeneities to be directly monitored with a vertical resolution as low as 20 µm. This enables nascent destabilization phenomenon (aggregates, sedimentation or creaming layers, coalescence, or agglomerates) to be detected and monitored at different intervals over time.

 

Dispersion Stability and Sizing

  • Quantification of stability—TSI index computation
  • Static multiple light scattering used for optical measurement of particle size and concentration
  • Natural state analysis, no mechanical stress applied
  • The need for sample preparation eliminated
  • Works with concentrated solutions (of up to 95% v/v)
  • 200x faster compared to traditional tests

Key Data

Migration Analysis

Phase formation is indicated by the local variation of light intensity, offering the following data:

  • Sedimentation information
  • Phase separation kinetics and thickness
  • Creaming rate
  • Hydrodynamic diameter
  • Particle migration speed

Size Variation Analysis

Global variation of light intensity is in accordance with the increase in size, offering the following information:

  • Agglomeration rate
  • Size evolution kinetics
  • Dispersibility ratio
  • Mean diameter
  • Coalescence rate

TURBISCAN Stability Index

TSI is a Turbiscan-specific parameter particularly developed for formulators to perform rapid standardization, comparison, and characterization of the physical stability of different formulations.

Any destabilization phenomenon that occurs in a specific sample will have an impact on the backscattering and/or transmission signal intensities as part of the aging process. The formulation having the highest intensity variation will be the one to vary in the most significant way, and hence the least stable.

The TSI calculation is simple yet robust and adds up the evolution of T or BS light at all measured position (h), on the basis of a scan-to-scan difference, over the total sample height (H):

Therefore, for every scan, a single TSI value is associated and “Destabilization kinetics” graphic can be developed, exhibiting TSI evolution with time. The figures below show a representative example on four samples: three new formulations (B, C, D) were compared to an old formulation (A), which was regarded to be stable.

The Turbiscan offers a quick and comprehensive overview of the stability that can be achieved. Within a few hours, it is possible to assess and predict the stability, days before the changes can be noted by the naked eye. Conclusions about the most stable formulation can be drawn by having just a single look at TSI.

In this case, Sample B offers higher or similar stability compared to the reference formulation (A). Samples C and D are less stable than the reference formulation.

 

Optical Measurement of Particle Concentration and Size by Static Multiple Light Scattering—Turbiscan®

TURBISCAN Stability Index - Picture 1
TURBISCAN Stability Index - Picture 2
TURBISCAN Stability Index - Picture 3
TURBISCAN Stability Index - Picture 4
TURBISCAN Stability Index - Picture 5
TURBISCAN CLASSIC
TURBISCAN LAB
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TURBISCAN AGS

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