Assessment of coating quality by use of dissolution kinetics

• Not only average coating thickness but thickness distribution is measured.
• Fast analysis, typically less than 10 min using dissolution kinetics.
• Coatings in the range of 1 to 10 μm on 400 μm core particles are measured.
• The method provides statistical certainty as it measures many particles.

Fluid bed coating of powder is widely applied in the industry. Analysis of the production batch in terms of coating thickness and its distribution within the population cannot be performed easily. Microscopic analysis to accurately measure the shell thickness of a particle lacks the ability to give statistical information of the population within a reasonable amount of time. In this work, a novel method based on measuring the effect of the coating and solving the involved inverse problem is proposed as a fast way to measure the shell thickness distribution in the sample. The method was tested with sodium chloride particles coated with varying amounts of maltodextrin. It could be shown that coating thickness distributions between 0.2 and 20 μm can be measured with significant differences between samples.

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