This work presents a new methodology for high-sensitivity analyses by capillary\nelectrophoresis (CE) with electrospray-ionization mass spectrometric (ESI-MS)\ndetection, based on electrophoretic focusing on an inverse electromigration dispersion\n(EMD) gradient. The technique is based on a robust electrolyte system providing a\ngradient of required properties, suitable for routine analyses of trace amounts of weak\nacids with pKa values between approx. 6.5 and 9. Examples analyses of several\nchlorophenols and sulfonamides are presented, with LODs around 3x10-9 M for spiked\ndrinking water without any sample pretreatment.