Blend Uniformity Monitoring System

When powdered components are blended during drug production, timing is critical. If the blending period is too short, the agitation has been insufficient to produce a homogeneous product. If blending time is too long, the particles will segregate.

Using the principles of thermal effusivity, C-Therm has developed the ESP™, a revolutionary, pharmaceutical blend uniformity monitoring system that:

  • Does not present possible contamination – eliminates the need to thieve samples
  • Can be phased in to pharmaceutical operations in logical steps
  • Can be retrofitted on existing blending or mixing equipment
  • Provides valuable information about the blending/mixing process for use in formulation R&D, scale up, and ongoing production
  • Can reduce operating costs and lost revenue due to discarded batches
  • Offers manufacturers a viable way to address Process Analytical Technology (PAT)

The ESP™ blend uniformity monitoring system consists of:

  • ESP™ Control Unit with portable laptop computer and Windows XP™ Professional operating system
  • 21 CFR Part 11 compliant software with automated functions for:
    • testing, display and reporting
    • establishing user permissions and authorization
    • archiving and audit trails
  • Eight (8) channel SWAP box
  • Eight (8) retrofittable, stainless steel effusivity sensors with food grade sensor surface

How the ESP™ Sensors Work

Using Relative Measure to Determine Blend Uniformity

In this application, at start-up, and every few minutes throughout the blending process, a number of sensors take effusivity measurements. To do this, the sensors supply a small amount of heat – approximately 2 - 3°C – to the powder with which they are in contact, and measure and interpret the amount of heat that remains at the sensor interface. The results of these measurements provide insight into the blending process, including the specific point in time at which blend uniformity has been optimized.

Early in the blending process, each of the sensors – located on the lid of the bender – provide differing measurements (see below). The variance between the sensors indicates an initial non-uniform blend that yields a high relative standard deviation (RSD).

As time progresses and uniformity is achieved, the measurements from the sensors converge and the RSD decreases. In this case, the RSD is a proxy for blend uniformity and will approach zero for a perfect mixture. The absolute measurement is not critical to the process.



1 480
2 460
3 400
4 410
5 320
6 280
7 250
8 300
346 +/- 23%
Blend uniformity is determined using relative measure – the individual results of the eight sensors are compared during blending. The uniformity of their readings correlates with the uniformity of the formulation.

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