Devices and methods for sample characterization

A method, comprising:

• in a microfluidic device, introducing an analyte mixture into a separation channel;
• applying an electric field across the separation channel to effect a separation of the analyte mixture via isoelectric focusing;
• continuously imaging the separation and mobilization of the analyte mixture by illuminating a first side of the microfluidic device through an optical slit, which provides optical access to the separation channel and detecting light passing through the optical slit and the separation channel;
• introducing an electrolyte into a separated analyte mixture after the separation;
• after introducing the electrolyte, expelling via electrospray ionization into a mass spectrometer substantially all of the analyte mixture from an orifice in line with the separation channel and in electrical communication with the separation channel's electric field;
• and
• correlating absorbance peaks of separated analytes in the separation channel with data from the mass spectrometer of the separated analytes after the expelling of the separated analytes.