The following is a quick review of the key questions and answers to familiarize you with the principles and operation of the effusivity sensor technology for blend uniformity monitoring.

Principles: What is the basis of the effusivity measurement? Fluorescence? Chemical Analysis?

Effusivity is a heat transfer property present in all materials in all formats - solid, liquid, paste, powder and gas. Effusivity combines thermal conductivity, density and heat capacity into one value. Effusivity is the property that dictates the interfacial temperature when two objects at different temperatures touch - ie when you touch a piece of metal versus a piece of wood.

Heat: How much does the probe's heating element have to heat up? Will the heat hurt my powder?

The sensor heats during the test time and measures the rate of heat loss simultaneously. In a typical powder 2 second test, the heating element increases in temperature by 1-2 °C.

Sample Size: How much sample is tested?

Nominally 150 mg, but the sample size is scalable with the test time. Longer tests cause the heat to penetrate further into the sample, increasing the quantity of material evaluated.

Absolute vs. Relative: How do absolute effusivity and relative effusivity compare in practice?

Absolute effusivity varies with particle size and material and can act as a screen of incoming raw material conformance to specs (see "pharmaceutical" category in the Technical Library). Relative values will be used in blend monitoring.

Compaction: Will the effusivity vary with different packing conditions that increase compaction?

Yes, but only until a threshold pressure is reached (see "pharmaceutical" category in the Technical Library). After that point, the effusivity reading will be consistent because the density becomes stable. It is pressure rather than applied weigh that is the variable involved.

Motion: Have you made measurements while blending or must you stop to get a reading?

At InterPhex in April 2002 (see "pharmaceutical" category in the Technical Library), an operable, retrofitted blender was introduced by Mathis. The final goal is measurement during blending with wireless transmission (see "pharmaceutical" category in the Technical Library).

Deblending: Can you see "deblending"?

Yes we can see deblending. The effusivity readings scatter as a result of component segregation and particle size distribution shifting (see "pharmaceutical" category in the Technical Library).

Low Dose: Have you tried the method on blending a low-dose (of the active ingredient) drug?

The technical sheet ESP7 (see "pharmaceutical" category in the Technical Library) represents results from a GSK commercially available product where the %LC assay is on a component under 1%. The actual sensitivity depends on the components involved (see "pharmaceutical" category in the Technical Library). Programs are underway to build our "portfolio" of successful correlations at low dose.

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