Capillary electrokinetic fractionation mass spectrometry ( CE k F / MS ): Technology setup and application to metabolite fractionation from complex samples coupled at‐line with ultrahigh‐resolution mass spectrometry

Capillary electrokinetic fractionation ( CE k F ) is investigated as a new, simple, and robust approach for semipreparative and analytical sample analysis based on p K a ‐dependant pH‐driven electrophoretic mobility. CE k F 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 (p K 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 F ourier transform MS , the p K a model was further illustrated in real samples into the structure prediction of important compounds in wine over two vintages. The established CE k F was successfully used to selectively fractionate sulfur compounds from the complex wine samples at pH 1.66. The proposed CE k F approach should allow in the future the simultaneous p K a evaluation of multiple constituents without complicated separation out of a complex mixture in metabolomics or environmental chemistry.