The invention provides, inter alia, methods of extracting an analyte from a solution comprising the steps of: passing a solution containing an analyte through an extraction channel having a solid phase extraction surface, whereby analyte adsorbs to the extraction surface of said extraction channel; purging bulk liquid from said extraction channel; and eluting the analyte by passing a desorption solvent through the channel. The invention further provides reagents, columns and instrumentation related to this and other methods.