dissolution apparatus

The dissolution apparatus is the standardized machine used to run a dissolution test — typically a row of glass vessels in a heated water bath, each holding the medium and a rotating stirrer that holds or stirs the dosage form. Standardizing the equipment is what lets a lab in one country reproduce a result obtained in another.

Pharmacopoeias define several apparatus types by number. Apparatus 1 is the rotating basket, which cages the dosage form in a mesh; Apparatus 2 is the paddle, the most common, which stirs medium around a unit resting at the vessel bottom; Apparatus 3 is reciprocating cylinder and Apparatus 4 is the flow-through cell, used for modified-release and low-solubility products. Key controlled variables are vessel volume, medium, temperature (usually 37 degrees Celsius), and rotation speed (such as 50 or 75 rpm).

Choice of apparatus and conditions strongly affects the result, so the method must be selected and qualified for the particular product. The apparatus is also mechanically calibrated and qualified, because small deviations in shaft alignment, wobble, or vessel dimensions can shift dissolution results enough to matter.