Reproducibility Problem

[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.

[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.

[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.

[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.