[SugarSkull]

Hi, I've been reading about dissolution and USP apparatus, particularly the basket and paddle models, but I'm having trouble finding out how they actually quantify the dissolution. So far all I can seem to find is general things talking about the different types of formulations you might want to use each for, or general notes on using the apparatus, but apart from stirring the formulation in a medium, I'm still not sure what the apparatus actually do. Any explanations or good resources would be great appreciated - I have an interview on Monday morning (UK time), so any help would be fantastic.

[Arkcon]

There are a few ways to quantify the dissolution.  The older style, a typical brand is Distek, requires you to pull a sample at the correct time point using a syringe with a cannula.  Methods vary, but there is a certain depth specified in the individual methods, defined by the protocols you manufacturer works under -- either USP (United States pharmacopeia, for sales in the US), there are also EP, JP and maybe there is still BP, and there may be more.

At any rate, once you've sampled from the six (or more depending on the experiment) chambers, you can run the samples in an HPLC (perhaps even a GC, if the active is volatile enough), or you can analyze by UV.  I recall one pharmaceutical, at a place I worked, required the six drawn samples to have some wet chemistry performed, either along with or separate from, a UV or HPLC quantification.

In fact, the more modern dissolution apparatus can do a constant, real-time, UV sampling of the dissolution medium -- but I never got to use cool systems such as those.  Auto-samplers for the preparation of vials for later HPLC runs directly from the dissolution media are also available.  I think, but I could be very wrong, that interfacing an auto-sampling dissolution rig directly to an HPLC auto-sampler is still an experimental dream, at least for mainstream, established, pharmaceutical manufacturers.  

[Arkcon]

For example, check out this PDF here: http://www.onlinepharmacytech.info/docs/vol2issue9/JPST10-02-09-01.pdf  It contains a subsection on experimental dissolution of a pharmaceutical containing the drug glipozide.  They apparently use UV quantification.

[SugarSkull]

That's fantastic, that's cleared up a lot of the mystery for me. One thing springs to mind - in either case, whether you're doing it manually or have an automated sampler, would the sample pass through a filter at some point, to stop any undissolved, solid particulate interfering with the analysis?

Thanks again for the help.

[Arkcon]

The procedure for each pharmaceutical is different, as given by the patent, or by a validated (that is rigorously tested and documented and cleared with Federal authorities) method.  But yes, the dissolution media ends up becoming a solution of soluble components, often with insoluble excipients suspended in it.  You use the proper syringe filter, and you discard the first few mls as a matter of policy.  Then, you collect a filtered sample for further tests.