Dissolution isn't just an important test for tablets and capsules, it can be used for a wide variety of other pharmaceuticals and medical devices.  One class of product that is tested with dissolution are semisolids such as medicated creams, gels, ointments, etc.  There are a number of ways that semisolids can be tested and they can be found in USP <1724> Semisolid Drug Products - Performance Tests.

One of these options is the Immersion Cell, also known as the Enhancer Cell which you can find in the below slide.  The great thing about the option is that you can use the same dissolution unit that you have for paddles and baskets, and convert it with just accessories for this type of testing.

The Enhancer/Immersion cell is usually used with a 200mL flat-bottom vessel and a minipaddle.  The enhancer cell itself is a chamber with an  adjustable height which your semisolid can be placed into.  The surface of the semisolid is evened out and a membrane placed on top - then secured by the washer and then by the retaining ring.  This allows for a fixed surface area to work with and allow for better comparisons (like intrinsic dissolution with the Woods Apparatus).

It is critical when working with semisolids to avoid air bubbles and ensure the membrane is handled carefully to avoid holes and tears.

Resource Person: Ken Boda (Dissolution Product Specialist at Agilent Technologies)