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Conductivity detection is the most popular detection method used in ion chromatography, and its hyphenation with suppressor technology provides two main benefits: i) mobile-phase background signal reduction and ii) analyte signal amplification. By integrating all chromatographic system components in a microfluidic platform, external band broadening can be reduced, improving separation efficiency. For this purpose, a microfluidic membrane suppressor has been constructed and evaluated for anion-exchange separations. Additionally, a holder has been constructed allowing to align and stack different modules (e.g. separation and suppressor module) while ensuring zero-dead-volume chip-chip connections. Ion suppression of the alkaline eluent was achieved via an acid-base reaction across a sulfonated poly(tetrafluoroethylene)-based membrane. This membrane was clamped between the two substrate plates of the suppressor module, accommodating micro-channels for the eluent and regenerant flow, respectively. The response and efficacy of the microfluidic suppressor was assessed for a wide range of eluent (OH-) concentrations, using 127 and 183 µm thick membranes, while optimizing the flow rate and concentration of the regenerant solution (H2SO4). The optimal eluent flow rate was determined at 5 µL/min, corresponding to the optimal flow velocity of commercially-available column technology, i.e., a 250 mm long column packed with 7.5 µm particles. When equilibrated at 15 mM KOH, a 99% decrease in conductivity signal could be obtained within 5 min with the application of 10 mM H2SO4 at a flow rate of 75 µL/min as regenerant solution. A background signal as low as 1.2 µS/cm was obtained after prolonged equilibration, which equals the performance of a commercially-available electrolytic hollow-fiber suppressor. When increasing the temperature of the membrane suppressor from 15 to 20?C, the ion suppression at high hydroxide concentrations was significantly improved allowing the application of ion strength up to 75 mM. The applicabilityof the microfluidic suppressor has been demonstrated with an isocratic baseline separation of a mixture of seven inorganic ions yielding a maximum plate number of 10,600 and a gradient separation of a complex ion mixture.

A polymer-based microfluidic device has been designed and constructed for comprehensive spatial two-dimensional chromatography, with each peak being characterized by its coordinates in the plane. The device manufactured from cyclic olefin copolymer (COC) features a first-dimension (1D) separation channel and 21 parallel second-dimension (2D) separation channels orientated perpendicular to the 1D channel. Compartmentalization of 1D and 2D flow by a physical barrier allowed for a preferential mobile phase flow path mainly restricted to the 1D separation channel, with a minimal dispersion into the 2D separation channels. After a 1D separation was halted, a radially-interconnected flow distributor of diamond-shaped pillars with diverging side-walls introduced the mobile phase for the 2D separation, allowing eluent inside the 1D channel to be fractionated and simultaneously injected into the 2D channels. A hydrophobic methacrylate-based monolithic stationary phase was polymerized in-situ in desired locations via aUV-initiated polymerization reaction employing a photo mask.