a method for measuring or identifying a component of interest in a biological system is disclosed herein . the method includes positioning a fibre within the biological system , the fibre being at least partially coated with a polymeric extraction phase for adsorbing the component of interest from the biological system , the extraction phase being positioned within the biological system ; adsorbing the component of interest onto the extraction phase ; removing the fibre from the biological system ; inserting the fiber into a nanospray needle ; flowing solvent through the nanospray needle ; desorbing the component of interest from the extraction phase into the solvent ; and nanospraying the desorbed component of interest into an analytical instrument for measurement or identification .