There are four apparatuses generally recognized by pharmacopeias (e.g. USP) and other regulatory bodies that may be used for drug dissolution testing for product evaluation. However, choosing one of these apparatuses, or any other, is difficult as there are no appropriate scientific or rationale criteria available for such selections.
All four apparatuses usually provide different results for the same product, and choice is left to the analyst to select one that meets the product’s expected behavior. This approach has two flaws: (1) indeed, these apparatuses are not measuring the same property (dissolution). Otherwise, the results would have been the same. A product cannot have four or more values for the same parameter; (2) a product, or its property, cannot be evaluated using itself as a reference to select a technique (apparatus).