  Multiparticle collision dynamics (MPCD) enables to simulate fluid dynamics
including both hydrodynamics and thermal fluctuations. Its main use concerns
complex fluids, where the solvent interacts with concentrated solutes, may they
be colloidal particles, polymers or electrolytes. A key difficulty concerns the
way one couples the fluid to the solute particles, without losing the key
advantages of the MPCD method in term of computational efficiency. In this
paper, we investigate the dynamical properties of solutes that are coupled to
the fluid within the collision step, {\em i.e.} when local momentum exchange
between fluid particles occurs. We quantify how the volume where momentum
exchange is performed (the size of the collision cells) constrains the
hydrodynamic size of the solute. Moreover, we show that this volume should be
taken smaller than the structural size of the solutes. Within these
constraints, we find that the hydrodynamic properties of a 1-1 electrolyte
solution are similar to the behaviour predicted by the Fuoss-Onsager theory of
electrolyte dynamics, and we quantify the limitations of the theory for 2-1 and
2-2 electrolytes. However, it is also clear that mapping the diffusion time
scale to that of a real system cannot be done quantitatively with this
methodology.
