We report an approach for the online coupling of digital microfluidics (DMF) with mass spectrometry (MS) using a chip-integrated microspray hole (μSH). The technique uses an adapted electrostatic spray ionization (ESTASI) method to spray a portion of a sample droplet through a microhole in the cover plate, allowing its chemical content to be analyzed by MS. This eliminates the need for chip disassembly or the introduction of capillary emitters for MS analysis, as required by state-of-the-art. For the first time, this allows the essential advantage of a DMF devicefree droplet movementto be retained during MS analysis. The broad applicability of the developed seamless coupling of DMF and mass spectrometry was successfully applied to the study of various on-chip organic syntheses as well as protein and peptide analysis. In the case of a Hantzsch synthesis, we were able to show that the method is very well suited for monitoring even rapid chemical reactions that are completed in a few seconds. In addition, the strength of the low resource consumption in such on-chip microsyntheses was demonstrated by the example of enzymatic brominations, for which only a minute amount of a special haloperoxidase is required in the droplet. The unique selling point of this approach is that the analyzed droplet remains completely movable after the MS measurement and is available for subsequent on-DMF chip processes. This is illustrated here for the example of MS analysis of the starting materials in the corresponding droplets before they are combined to investigate the reaction progress by DMF-MS further. This technology enables the ongoing and almost unlimited tracking of multistep chemical processes in a DMF chip and offers exciting prospects for transforming digital microfluidics into automated synthesis platforms.

This paper reports a new method for studying stereoselective catalyzed reactions at a small scale. For this purpose, a micro‐sized chemical reactor and a chiral chromatographic column were integrated on a single microfluidic chip hyphenated to mass spectrometry. By running the integrated reactor in truly continuous‐flow operation with an automated injection strategy, catalytic processes and their stereoselectivity can be observed over an extended range of time with significantly small consumption of samples, solvents, and catalytic material.

A highly integrated microfluidic device is presented for the parallelised study of stereoselective heterogeneous catalytic processes. For the first time, multiple packed-bed µ-flow reactors are combined with a chiral separation...

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The Front Cover illustrates a vortex that engulfs entire laboratory equipment and turns it into a single chip unit on the other side. In their Full Paper, H. Westphal, R. Warias et al. present a method to study immobilized organocatalysts and their performance in stereoselective transformations. This is done by utilizing a single chip‐based device combining a packed bed microreactor running in a truly continuous fashion and a miniaturized chiral HPLC unit coupled to Electrospray Ionization Mass Spectrometry. Not only insights into the catalyst's steady states and overall long‐term activities can be investigated, but also it is possible to clarify their stereoselectivity right on‐stream. Thus, this method provides a sustainable and rapid method for catalyst discovery and optimization at smallest scales. More information can be found in the Full Paper by H. Westphal, R. Warias et al.