HPLC method validation: sample assay solution stability

[Rob Burgess]

Hi there,

Just wondering how folks would do this practically say for a tablet solution. Would they prepare fresh standards at each timepoint to assess the assay solution stability or could you just use existing standards that had been pre-determined to be "in-date"?

Hope this question makes sense

[Consumer Products Guy]

I believe regulatory agencies assume that calibration standards are to be made fresh each day of use unless you have documented their stability. I haven't seen anything in USP detailing stability of any of its solutions.

[Rob Burgess]

Hi CPG,

Let's say I have documented evidence that the standards are stable - is it then deemed "acceptable" to use these "old within date standards" to assess solution stability of samples (tablet, capsules etc)?

Any other views? I asked around analysts in my own lab and got a difference of opinion some say fine some say use fresh standards every time for assay solution stability validation? Personally, I have and would say it is ok to use old standards that are proven to be stable in solution i.e. (99-101% or original assay values).

[Consumer Products Guy]

I'd say that you have documentation of the stability of the solution, like area of peak divided by its concentration is equivalent to that of freshly prepared standards, then you've used good science and that should be readily defendable.

But that's just my scientific opinion and logical opinion.

[LC_labrat]

Although I agree if you have standard solution stability you can use the standards to assess the tablet solution stability, I personally would still prepare fresh standards.

It's simple and wouldn't bring any questions as to the validity of the sample solution stability data. If you already have differing opinions in your laboratory I just wouldn't spend any further time trying to justify it.

[JGK]

Was standard stability not addressed as part of the initial method vaildation?

Coming from a GLP environment or method vaildation SOP covered this including how to test and acceptance criteria.

If yours doesn't, stick to preparing fresh each time. Unless you have a uniform process for stability determination you are opening up the proverbial "can of worms" http://en.wikipedia.org/wiki/Can_of_worms

[Alex Buske]

Our pragmatic aproach is to set up a series (often n=6) of sequences with standards and samples. They run over lets say 72 hours, if necessary with blanks in between. In the end we compare peak areas of standard solutions and if there is no or little (predefined!) change, we regard standard solutions as stable. Within each sequence we calculate the samples on basis of standards from the same sequence (if standard solutions are stable). If results just change in predefined limits, sample solutions are regarded as stable.
No problems so far with agencies and corporate auditors.

Alex

[DSP007]

If the standards are stable - why not use them after 24 or 72 hours. The main problem - the volatilization of solvent. Another problem, such as parabens-air oxidation

Well, keep the standards in a glass vial and in refrigerated

[Rob Burgess]

An additional point/query.

For those that would prepare fresh standards each time to assess their "sample (tablet, capsule etc) solution stability" - does this not put out the message that fresh standards are thus required for all types of analyses.

i.e. The following scenario's are in conflict:

1) sample solution validation - must use fresh standards - i.e. do not trust validated within date "old" standards

2) BUT for routine testing e.g. "clinical" batch release, ICH stability samples you can "get-away" with using in-date validated standard solutions

I wouldn't like to defend this stance to a regulator inspector. i.e. must use fresh prepared standards for sample solution stability validation but can use old "within date" validated standards for routine samples.

PS. Is there any official guidance out there that explains what is allowed with respect to all of this?

[lynzjm]

This makes perfect sense to me as I used to do exactly this type of work, I was a stability and validation study director in a pharmaceutical lab. We asked similar questions. In the UK we were allowed to use standards which were in their pre-determined stability range throughout. But when I was doing my studies I would assess the validation results first, for example your "in-date" standards criteria for passing could be 90-110% and if they passed yet were passing at the extreme limits of this range towards the end of the "stability window" then they could be out slightly which would affect your results if this makes sense.

We also did analytical solution stability as well as the actual drug formulation stability i.e. the drug formulation/tablet solution etc stored and diluted down each day AS WELL as the drug formulation/tablet solution diluted down to the analytical level and stored also. Both were often very different.

I think if you check the regs for your area they should be ok to use but its best to assess on a case by case basis, using your validation data as evidence for a regulator if required, for each I think depending on your validation data!

Lynz