Bioequivalence and Bioavailability Forum

Dear all,

I would not worry too much about a small difference in injection volume (e.g. 40 vs. 50 µl), but I'm not sure what the interest of such small variations could be. Better stick to what has been validated.

For higher variations I would agree with Helmut that this should be tested during the method validation. Remember also that with MS methods, matrix effects can vary depending on the amount of matrix injected: you can have a sort of threshold effect, where you will have no effect for low amounts of matrix (low volume injected) and suddenly see matrix effects appear for higher amounts of matrix (higher volumes injected). There is a very nice figure in this paper, where they obtained a higher signal after a 1/10 dilution of their extracts (well, that's plant material and not plasma, but the principle will be the same):

M. Villagrasa, M. Guillamon, E. Eljarrat, D. Barcelo
Matrix effect in liquid chromatography–electrospray ionization mass spectrometry analysis of benzoxazinoid derivatives in plant material
Journal of Chromatography A, 1157 (2007) 108–114

Regards
Ohlbe