Surfaces and Coatings

Quantification of Tablet Surface Roughness

Coatings are applied to pharmaceutical tablets to optimize an array of different features including, swallowability, product stability and the controlled release properties of the active pharmaceutical ingredient (API). Both surface finish and coating thickness are important features that must be characterized during both product research and development and tablet manufacturing. Further, energy dispersive X-ray spectroscopy can be employed to quantify the chemical composition of the coating with very high spatial resolution.

Quantitative assessment of surface roughness can be measured using the Zeta-20 3D optical profilometer. Conventional high-pass filtering techniques can be used to remove the curvature of the tablet itself without effecting the micro/nanoscale roughness of the surface.


Surface finish analysis a brand name drug product (left) versus a generic competitor (right)

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Note above that the private label drug product had a surface roughness greater than 3.8x that of name brand tablet. This could have significant impact on tablet swallowability, shelf life and the time release profile of the API.


SEM Analysis of Tablet Coating Thickness and Chemical Composition.

In addition to the quantitative determination of coating roughness. It is also important for pharmaceutical companies to understand both the thickness and chemical composition of tablet coatings.

The Phenom Desktop SEM is unique in it's capacity to evaluate pharmaceutical tablet coatings:

  • Back-scatter electron detection allows for the unambiguous determination of elementally different materials without the need for EDS.
  • The high-brightness CeB6 source produces unparalleled image quality while maintaining an extremely long lifetime.
  • The integrated EDS detector with mapping enables quick determination of elemental composition.
  • Integration with Quartz PCI/CFR enables imaging in compliance with FDA 21 CFR Part 11.

Coating thickness comparison between a brand name drug product (left) and a generic competitor (right)

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The coating surrounding the brand name tablet is approximately 360 µm thick while the private label tablet is about 25 µm. This discrepancy can have significant impact on the time release properties of the API.

EDS Analysis of Pharmaceutical Compounds

Energy Dispersive X-ray spectroscopy can be used to determine the elemental composition of pharmaceutical drug compounds and excipients and ascertain the distribution of additives like talc or TiO2 within tablet coatings. The bright dots on the surface of the coating below correspond to distributed TiO2 particles commonly used as a pigment.

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