I cant find rapramycin; do you mean "rapamycin".
If you do, I'm surprised that you expect a compound with 5x >C=O, 2x -OH groups and MW 914 (underivatized) to have sufficient volatility to be amenable to GC analysis.
Have you done a lit. search, or any homework, on this compound ?
You should be doing HPLC; many refs. out there.