Hyphenation of Production-Scale Free-Flow Electrophoresis to Electrospray Ionization Mass Spectrometry Using a Highly Conductive Background Electrolyte

Coupling Miniaturized Free-Flow Electrophoresis to Mass Spectrometry via a Multi-Emitter ESI Interface

We present a novel multi-emitter electrospray ionization (ESI) interface for the coupling of microfluidic free-flow electrophoresis (μFFE) with mass spectrometry (MS). The effluents of the μFFE outlets are analyzed in near real-time, allowing a direct optimization of the electrophoretic separation and an online monitoring of qualitative sample compositions. The short measurement time of just a few seconds for all outlets even enables a reasonable time-dependent monitoring. As a proof of concept, we employ the multi-emitter ESI interface for the continuous identification of analytes at 15 μFFE outlets via MS to optimize the μFFE separation of important players of cellular respiration in operando. The results indicate great potential of the presented system in downstream processing control, for example, for the monitoring and purification of products in continuous-flow microreactors.

Multiplexed Online Monitoring of Microfluidic Free-Flow Electrophoresis via Mass Spectrometry

Free-flow electrophoresis is a tool for the continuous fractionation of electrically charged analytes. In this study, we introduce a novel method to couple microchip-based free-flow electrophoresis with mass spectrometry. The successive connection of multiple microchip outlets to the electrospray ionization source of a mass spectrometer is automated using a multiposition valve. With this novel setup, it is possible to continuously fractionate and collect compounds while simultaneously monitoring the process online with mass spectrometry. The functionality of the method is demonstrated by the successful separation and identification of the biomolecules AMP, ATP, and CoA, which are fundamental for numerous biochemical processes in every organism.

Visualization of Streams of Small Organic Molecules in Continuous-Flow Electrophoresis

Continuous-flow electrophoresis (CFE) separates a stream of a multicomponent mixture into multiple streams of individual components inside a thin rectangular chamber. CFE will be able to benefit flow chemistry when it is both compatible with nonaqueous solvents utilized in organic synthesis and capable of generically detecting streams of small organic molecules. While stable nonaqueous CFE has been demonstrated, generically detecting molecular streams has not been achieved yet. Here we propose a general approach for molecular stream visualization in CFE via analyte-caused obstruction of excitation of a fluorescent layer underneath the separation chamber-fluorescent sublayer-based visualization (FSV). The concept of FSC-based visualization has been adapted from visualization of small organic molecules on fluorescent plates in thin-layer chromatography. We designed and fabricated a CFE device with one side made of quartz and another side made of UV-absorbing visibly fluorescent, chemically inert, machinable plastic. This device was demonstrated to support nonaqueous CFE of small organic molecules and quantitative detection of their streams in real-time with a limit of detection below 100 μM. Thus, CFE may satisfy conditions required for its seamless integration with continuous flow organic synthesis in flow chemistry.

Continuous flow electrophoretic separation - Recent developments and applications to biological sample analysis

Continuous flow electrophoretic separation with continuous sample loading provides the advantage of processing volumes of any sizes, as well as the benefit of a real-time monitoring and optimization of the separation process. In addition, the spatial separation of the sample enables collecting multiple separated components simultaneously and in a continuous manner. The separation is usually performed in mild buffers without organic solvents and detergents (sample biological activity is retained) and it is carried out without usage of a solid support in the separation space preventing the interaction of the sample with it (high sample recovery). The method is used for the separation of proteins/peptides in proteomic applications, and its great applicability is to the separation of the cells, cellular organelles, vesicles, membrane fragments, and DNA. This review focuses on the electrophoretic separation performed in a continuous flow and it describes various electrophoretic modes and instrumental setups. Recent developments in methodology and instrumentation, the integration with other techniques, and the application to the biological sample analysis are discussed as well.

Continuous flow chemistry: where are we now? Recent applications, challenges and limitations

A general outlook of the changing face of chemical synthesis is provided in this article through recent applications of continuous flow processing in both industry and academia. The benefits, major challenges and limitations associated with the use of this mode of processing are also given due attention as an attempt to put into perspective the current position of continuous flow processing, either as an alternative or potential combinatory technology for batch processing.

LC/MS at the whole protein level: Studies of biomolecular structure and interactions using native LC/MS and cross-path reactive chromatography (XP-RC) MS

Interfacing liquid chromatography (LC) with electrospray ionization (ESI) to enable on-line MS detection had been initially implemented using reversed phase LC, which in the past three decades remained the default type of chromatography used for LC/MS and LC/MS/MS studies of protein structure. In contrast, the advantages of other types of LC as front-ends for ESI MS, particularly those that allow biopolymer higher order structure to be preserved throughout the separation process, enjoyed relatively little appreciation until recently. However, the past few years witnessed a dramatic surge of interest in the so-called "native" (with "non-denaturing" being perhaps a more appropriate adjective) LC/MS and LC/MS/MS analyses within the bioanalytical and biophysical communities. This review focuses on recent advances in this field, with an emphasis on size exclusion and ion exchange chromatography as front-end platforms for protein characterization by LC/MS. Also discussed are the benefits provided by the integration of chemical reactions in the native LC/MS analyses, including both ion chemistry in the gas phase (e.g., limited charge reduction for characterization of highly heterogeneous biopolymers) and solution-phase reactions (using the recently introduced technique cross-path reactive chromatography).