Incubating blood with LPS prior to ELISA - Interleukin-6 ELISA (Oct/15/2009 )

For my honors thesis, I am studying the effects of social stress on Interleukin-6 levels in rats. I am planning on incubating the blood with LPS ex-vivo to simulate an immune challege and stimulate an immune response. I have ordered the LPS (E. coli prepared by phenol extraction.) I am confused as to how to add this to the blood--- the papers I have read have all said 50ng/ml of LPS, but mine came in a powder form, so I am assuming it needs to be diluted somehow? It can't mean 50ng of the power per ml of blood... I am a psychology major, and though I am very familiar with running ELISA's, I don't have anyone to ask for advice on this matter. Any help would be greatly appreciated.

"the papers I have read have all said 50ng/ml of LPS"
This mains you have to solve 50 ng of LPS in 1 ml milli-Q but check the leaflet that came with the LPS to confirm that this correct otherwise contact tour supplier for confirmation of the solvent.