A fibrous mat (100) for use in taking a metabolome sample and for use in desorption of the metabolome sample. The fibrous mat (100) comprises an open network of at least one polymer-based nanofiber (110), wherein the diameter of the at least one nanofiber is ranging between 50 nm and 1500 nm, and characterized in that a cover layer is provided at a top and/or at a bottom of the open network of at least one nanofiber to exclude particles with a size larger than 2000 Da from interacting with the open network of at least one nanofiber by blocking and/or excluding access to these particles.