Good Dissolution practices require you to keep your system as reproducible and aligned as possible to ensure quality data.  Part of that is always returning your dissolution components (vessels, paddles, baskets, basket shafts) to the same position on the dissolution unit each run.  


When you qualify a dissolution system, you are qualifying each position of the dissolution unit as its own assembly.  Each position is a marriage of that vessel and shaft/basket.


Not controlling the position of your components can lead to several problems in the dissolution lab.  First, the system has not been measured with random mixtures of components - and some combinations of shafts and vessels may lead to a position(s) that aren't in alignment.  For example, if you have a vessel skewed one way slightly and a shaft skewed the other way slightly - that combination may fail centering. 


Second, investigations and trending are much easier when you control your components. Often times, dissolution failures can be traced to a component such as a bent or dirty basket or a scratched vessel.  That isn't something that is easily caught if those components are moving around to different positions on the unit.  


The error would appear random without these controls, whereas if you control for this you may find that one position is showing a consistently high or low result.  That allows you to focus your investigation on just that position and its components.


Keeping your components in the same position is something required if you are doing the ASTM or FDA Mechanical Qualification Procedure.  This is also required when doing the USP Prednisone Performance Verification Test.  It is also mentioned in the USP Toolkit 2.0:

Assembly— All vessels and individual parts of the stirring elements (shafts, baskets, paddles or paddle blades) should be uniquely identified, documented, and kept in the same position in the same test assembly for all dissolution runs. For ease of identification and record keeping, apparatus positions on the vessel support plate of the dissolution test assembly should be identified systematically.


Dissolution accessories need occasional replacement due to wear and tear, accidents, and corrosion.  It is important when we replace these components, that we ensure that the dissolution unit is re-qualified for use.


In dissolution, reproducibility is everything. So take it seriously and precisely.


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