Combining microfluidics and mass spectrometry

Resolution of components in complex mixtures for identification and characterization is a major problem in biotechnology. Technologies differentiating compounds in space or time reduce sample complexity and expand the applicability of Mass Spectrometry (MS). Front-end sampling is key to coupling separations and dynamic surfaces to electrospray ionization (ESI) for MS detection. Described herein are applications of such a microfluidic probe.;The liquid microjunction surface sampling probe (LMJ-SSP) transfers molecules into an ESI source from atmospheric pressure. Studies showed probe capabilities coupling to reservoirs of bioanalysis devices and scanning for molecules on flat, hydrophobic surfaces. However, experiments showed some biologically interesting surfaces were incompatible with continuous scanning due to liquid junction loss. This led to making direct contact for extraction of discrete spots; a process referred to as Direct Extraction Electrospray Probing (DEEP). DEEP-MS allows a broad range of surfaces to be sampled, the extent of dilution to be controlled, and the spatial resolution optimized. DEEP-MS was applied to chemical imaging problems where compound distributions on grape skins were analyzed.;Skin Excreted Metabolite Investigating Direct Extractive Electrospray Probing (SEMI-DEEP) is a non-invasive DEEP application to human processes in vivo. Natural skin excretion of analytes provides a temporal picture of metabolic processes in challenge/response experiments. Data from probing showed quantitative and qualitative variations of compounds over time, between individuals, and dependant on specific metabolic challenges. SEMI-DEEP-MS could generate new methods in point-of-care clinical diagnostics with further study of location optimization and person-to-person variation work.;Methods of modifying surfaces to enhance compound availability were also investigated. Direct Extraction Electrospray Probing for Electrophoretic Recovery (DEEPER) applied the probe to gel systems. DEEPER-MS has the potential to make analysis of gel-separated species more efficient through detection without band excision or extensive sample treatment.;By bringing surface species to ESI sources, DEEP, SEMI-DEEP, and DEEPER bring to surface systems the benefits of MS, where detecting small changes in small amounts of compounds with broad distributions of sizes and concentrations could have extensive value in medical and biological research.