I would very much appreciate for all of your expert opinions on the following:

I am analysing a drug and have validated the method in human plasma and fetal rat tissue. Can I use the validated calibration curve for human plasma as a calibration curve for other body fluids? And can I use the standard calibration curve for fetal rat tissue for the analysis of human fetal tissue?

I cannot find any information regarding biological matrix effects for sample preparation/analysis.

I would very much appreciate if someone can offer some advice on my question. Thank you!

normally you can switch between identical bodyfluids from different species (normally based on exp.), but unfortunately it can happen that recovery and selectivity turns out differently, which gives wrong results
therefore FDA-recommendations (may 2001) ask for validation of the fluid from the second species

I am not sure what kind of detector you are using, but the matrix can have a tremendous influence on the signal. This is particullarly true for LCMS. Fluorescence, and to a lesser extent, absorbance, can also be influenced by matrix.

Hello,
You can find such informations when looking into instruction manuals from several manufacturers. They recommend different protocol for urin and plasma, and I agree with Hermann Bozler.
From Varian you can get a free CD-rom with SPE applications, called CP-Scanview. Waters can provide you with useful information on their SPE products, also Merck and other manufacturers have such information available. Sometimes you need a different surface chemistry on the SPE material for different bodyfluids.
Gerhard