  We analyse the concentration of solid particles in vortices created and
sustained by radial buoyancy in protoplanetary disks, i.e. baroclinic vortex
growth. Besides the gas drag acting on particles we also allow for
back-reaction from dust onto the gas. This becomes important when the local
dust-to-gas ratio approaches unity. In our 2D, local, shearing sheet
simulations we see high concentrations of grains inside the vortices for a
broad range of Stokes numbers, ${\rm St}$. An initial dust-to-gas ratio of
1:100 can easily be reversed to 100:1 for ${\rm St}=1$. The increased
dust-to-gas ratio triggers the streaming instability, thus counter-intuitively
limiting the maximal achievable overdensities. We find that particle trapping
inside vortices opens the possibility for gravity-assisted planetesimal
formation even for small particles ($\rm{St}=0.01$) and low initial dust-to-gas
ratios (1:$10^4$)
