  We propose a method to separate enantiomers in microfluidic or nanofluidic
channels. It requires flow profiles which break chiral symmetry and have
regions with high local shear. Such profiles can be generated in channels
confined by walls with different hydrodynamic boundary conditions (e.g. slip
lengths). Due to a nonlinear hydrodynamic effect, particles with different
chirality migrate at different speed and can be separated. The mechanism is
demonstrated by computer simulations. We investigate the influence of thermal
fluctuations (i.e. the P\'eclet number) and show that the effect disappears in
the linear response regime. The details of the microscopic flow are important
and determine which volume forces are necessary to achieve separation.
