Posting: # 19026
Please I need an explanation on what is the difference between an in-line filter and filter at end of sampling probe.
I saw a dissolution methodology which stated thus:
"...tablet was placed into a dissolution medium and then 5ml of dissolution was withdrawn at the stipulated time and immediately filtered through a syringe filter."
This methodology was queried by seasoned regulators. They requested that the filters should be in-line or at the end of the sampling probe or both.
What do they mean by that statement? Isn't that syringe filter considered as an in-filter? What do they mean by filter at end of sampling probe? What's the difference between an in-line filter and a filter at end of sampling probe?
I will really appreciate an assistance with this puzzle.
Posting: # 19050
» I saw a dissolution methodology which stated thus:
» "...tablet was placed into a dissolution medium and then 5ml of dissolution was withdrawn at the stipulated time and immediately filtered through a syringe filter."
» This methodology was queried by seasoned regulators.
An interesting question and just shows that some regulators have nothing better to do with their time.
1st a direct answer to your question - no what you are doing is not in-line filtering it is off line filtering because you are pulling the sample from out of the dissolution system and then filtering it - so off line. However that is how most of us did this for years and it is perfectly OK.
The USP says withdraw the sample (which to me implies off line) and has a foot note Test specimens are filtered immediately upon sampling unless filtration is demonstrated to be unnecessary.
In fact in terms of validation to validate an automatic method with in-line sample you are expected to compare the results to the manual method. The Ph.Eu is essentially the same.
» They requested that the filters should be in-line or at the end of the sampling probe or both.
Are you sure that you understood them—if as you say that really said in-line or at the end of the sampling probe or both, then I would also like to know what they mean by "both" – two sets of filter? Surely not.
However, if they are really giving you a hassle on this - do one experiment with both in-line and off-line and demonstrate that there is no difference.
I must add that maybe you were doing something wrong with your off-line filtration which led to the comments but otherwise I cannot see any justification for their criticism.
Hope that helps – regards Malcolm Ross
Edit: Full quote removed. Please delete everything from the text of the original poster which is not necessary in understanding your answer; see also this post #5! [Helmut]