Chromatography Forum

Please, help us to clarify the dilemma:
According to SOP in our company, it is defined that reference solution in case of assay testing should be injected 5 times and that RSD must be ≤2.0%. What to do in a case when 1 out of 5 consecutive injections is not good? For example: what to do in a case if all peak areas in 4 of 5 chromatograms are 100000, and 1 of 5 chromatograms has peak area 120000? Do we have to disregard only 1 injection in a sequence, and repeat once again injection of reference solution, or we must inject 5 times again from the start in order to have 5 consecutive injections? Please, notify that we also have the rule that reference solution must be injected after each 6th injection of test solution or 3 hours, as a control and it must also be whithin above mentioned criteria of ≤2.0% - which means that we also have this confirmation that system is functioning properly.
What is your advice in this case: to re-inject the reference solution once more, or to repeat the entire sequence?

First You have to investigate and find the reason why one injection is bad.
Then fix it (or at least attempt "refresh" of HPLC system to make sure all is set up correctly and there are no problems with caplillaries and etc.)
Then start sequence from the beginning.

First You have to investigate and find the reason why one injection is bad.
Then fix it (or at least attempt "refresh" of HPLC system to make sure all is set up correctly and there are no problems with caplillaries and etc.)
Then start sequence from the beginning.

Yes, i agree. This is the correct procedure that is applicable in your case. You have to figure out what happened, fix the problem, and restart the whole sequence.

PS. we've been having a similar issue with one of our waters systems(with no obvious explaination), and we had long debates on what to do because the standard solution and injector were clearly ok, but the final conclusion was that you need to reinject everything.