Chromatography Forum

I am trying to validate an LC/MS method for an analyte and metabolite (using an analogue internal standard).

What I have noticed is that my instrument response for my system suitability injection varies greatly from day to day (around 10 fold) even though I am injecting the same solution each day!

Any ideas?

first thing I would think of could be the stability of the analytes or the internal standards.

dear this might be due to the sovent used. we observe the same thing for lcms while using different brands. just check out.