High-resolution isoelectric focusing of seven fluorescent pH markers using a μFFE chip. A gradient from 4 to 10 pH units was established using preseparated ampholytes. The fluorescent marker had pIs of 4, 5.1, 6.2, 7.2, 8.1, 9, and 10.3. Reprinted in part with permission from Kohlheyer et al. (2007) Anal. Chem. Copyright 2007 American Chemical Society