First dissolve your FA free BSA in your solution (i.e. cell culture media or Krebs). I place the BSA solution onto something that rocks/rotates. Leave it until the solution is clear and all the BSA has dissolved. Then make up your selected concentration of FA in ethanol or as instructed by manufacturer as a concentrated stock. Make sure you correct for the density if it is a liquid. Then add stock to BSA solution. The BSA will drop out of the solution when the FA is added. Just heat to 37C degree and once the complete FA+FA free BSA solution is clear, then it is conjugated and can be used. Good luck.

Thank u sarah are using Sigma products FFA and BSA ???

sigma for the FAs and merck for BSA. It should be no problem though.

Also check your FA free BSA is endotoxin free too or you can get activation of immune signalling pathways too.