Why is my analyte response changing?

[sb2010]

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?

[promochrom]

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

[pliva]

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