the present inventions relate to micro - fluidic devices and related methods of fractionating samples of analytes , such as peptides or proteins , according to their isoelectric points . the disclosed micro - fluidic devices and related methods provide a fractionation sufficient to enhance the performance of immunochemistry and / or tandem liquid chromatography - mass spectrometry workflows . such methods and devices are capable of fractionating complex samples in a short time , using a small amount of sample , do not require high voltages and are further characterized by their high degree of reproducibility and ease of use .