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Reproducibility Problem
Posted: Tue Apr 30, 2019 1:00 am
by Shalom
I have problems of reproducibility, in an Alliance 2695, have mounted 3 systems of 6 injections, and always in the three systems the first injection is the one that does not play like other 5. im not have idea what it is.
Re: Reproducibility Problem
Posted: Thu May 09, 2019 3:28 am
by tom jupille
It's hard to give a specific answer without a lot more information about your method, but just as a guess: If your separation involves a gradient, the pre-equilibration time can have an impact on results. In an automated system, the equilibration time between injections is constant *except* for the first injection of the day. My practice has been to always make the first injection a blank or "dummy" to avoid that problem.
Re: Reproducibility Problem
Posted: Thu May 09, 2019 1:51 pm
by Consumer Products Guy
My practice has been to always make the first injection a blank or "dummy" to avoid that problem.
We ALWAYS did that; likely learned that from you in the late 1970s !!!
We wrote that into our test procedures so there would be no confusion, and for our cGMP compliance.
Re: Reproducibility Problem
Posted: Thu May 16, 2019 10:25 pm
by Sallybeetle
Tom Jupille and Consumer Products Guy:
Great Advice! I must have learned this from reading your advice over the years.
I generally include 1 - 4 equilibration injections of standard prior to system suitability to condition the system, depending upon the assay.
Also, I suggest adding time to the re-equilibration at the end of the chromatogram or between injections, if possible.