mass transfer - band-broadening effect due to the lack of sample equilibrium between the mobile phase and adsorbent surface, usually due to the narrow pore ; this effect is expressed by the third term of the van Deemter equation.

See also mass transfer.

mean pore diameter - the average pore diameter of the pore in a porous packing. The pore diameter is important in that it must allow free diffusion of solute molecules into and out of the pore so that the solute can interact with the adsorbent surface. In SEC, the packings have different pore diameters, and therefore molecules of different sizes can be separated. For a typical adsorbent such as silica gel, from 80 to l25 pore diameters are most popular. For packings used for the separation of biomolecules, pore diameters 300 are used.

See pore size and distribution.

mesh - usual way to characterize particle size; the mesh number indicates the number of wires per inch of the sieve through which the particles are passed.

micellar chromatography - the addition of micelles to the mobile phase to effect separations. The micelles act as displacing or partitioning agents and provide another parameter that can be used to change selectivity.