I am traveling to DCA-CLT-MAD this summer on US Airways. I'm tossing the idea around of tagging on a short hop from MAD to Barcelona when I land in Madrid. I already have the tickets to Madrid, but none to Barcelona as of yet.

My question is, if I buy tickets to Barcelona leaving a couple hours after landing in Madrid, would it be possible to interline my bags from DCA all the way to the Barcelona flight?

TIA