The appearance of gaps, vertical lanes lacking protein spots at the cathodic end of 2-D maps generated with wide range IPG-strips exceeding a pH value of 9, is shown to depend on the electro-osmotic transport of water into the IPG-strip. Substitution of urea solution with water is demonstrated to increase the hydrolysis rate of polyacrylamide in IPG-strips explaining the gap formation. The use of 8 M urea or thiourea/urea solutions in the electrode wick enables overnight focusing without the appearance of gaps.