There's a nice paper on this topics:
P.H. Barry and J.W. Lynch "Liquid junction potentials and small cell
effects in patch clamp analysis", J. Membrane Biol. 121: 101-117, 1991.
E. Neher "Correction for liquid junction potentials in patch clamp
experiments", Meth. Enzymol. 207: 123-131, 1992.