Capillary　electrokinetic　fractionation　(CEkF)　is　investigated　as　a　new,　simple,　and　robust　approach　for　semipreparative　and　analytical　sample　analysis　based　on　pK(a)-dependant　pH-driven　electrophoretic　mobility.　CEkF　was　optimized　with　contactless　conductivity　detection　and　conducted　with　10　kV　reverse　voltage　for　10　min,　then　coupled　on/at-line　to　ESI/MS.　We　propose　a　semi-empirical　model　with　14　representative　compounds　based　on　the　correlation　between　sample/medium　pH　regulating　the　partial　charge,　the　electrokinetic　loading　of　the　capillary　and　intensity　(I)　of　analytes.　According　to　the　model,　an　empirical　function　(I　=　f　(pH))　could　be　derived　to　calculate　the　acid　dissociation　constant　(pK(a))　of　various　model　compounds　based　on　their　pH-dependant　MS　intensity　profiles　with　the　RSD　＜　4.05.　Using　the　ultrahigh-resolution　of　ion　cyclotron　resonance　Fourier　transform　MS,　the　pK(a)　model　was　further　illustrated　in　real　samples　into　the　structure　prediction　of　important　compounds　in　wine　over　two　vintages.　The　established　CEkF　was　successfully　used　to　selectively　fractionate　sulfur　compounds　from　the　complex　wine　samples　at　pH　1.66.　The　proposed　CEkF　approach　should　allow　in　the　future　the　simultaneous　pK(a)　evaluation　of　multiple　constituents　without　complicated　separation　out　of　a　complex　mixture　in　metabolomics　or　environmental　chemistry.