Sensitivity checks at the end of a run (for sys suit purpose

[Rob Burgess]

How do people feel about the need to run a sensitivity check (e.g. prepared at 0.05% of main peak concentration/loading) at the end of the run to meet system suitability requirements for related impurity tests?

The problem as I see it is that with the majority of our HPLC systems we get carryover of the main peak in preceding blanks at the end of the run, which would thus interfere with calculating the resulting s/n of sensitivity check solution. Sometimes it can take 3 or more blank injections to try and remove the carryover but it is variable from compound to compound. Needle washing doesn't seem to help as the carryover must be occurring in the seals or loop of the injector itself.

Note if the sensitivity check is performed up front before main peak loading at 100% then obviously we won't be seeing carryover.

So, do we feel that we have to demonstrate sensitivity at the end of the run also or is demonstrating at the start of the run (before carry-over issues can manifest themselves) enough?

[tom jupille]

I would do the sensitivity check at the beginning of the run as you suggested (and for the same reason). If you need to verify at the end of the run, I would think that checking that the noise level and the response of a mid-level standard should be sufficient to verify that the S/N ratio is consistent.