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In this technical note, we demonstrate the hyphenation of production-scale free-flow electrophoresis (FFE) and sheathless electrospray ionization mass spectrometry (ESI-MS). In contrast to previous hyphenation approaches, we used a highly conductive background electrolyte (BGE) required for production-scale FFE. We found that this kind of BGE as well as a production-scale setup leads to significant electric interference between FFE and MS. This interference prevents steady-state FFE operation. We examine this interference in detail and discuss possible solutions to this issue. We demonstrate that the straightforward grounding of the transfer line removes the influence of ESI-MS on FFE, but creates a current leak from the ESI interface, which adversely affects the ESI spray. Furthermore, we show that only the electrical disconnection of the ESI probe from the FFE-MS transfer line suppresses this undesirable current. In order to facilitate the electrical disconnection we used a low conductivity, silica-based ESI probe with withdrawn inner capillary. This approach allowed the interference-free hyphenation of production-scale FFE (using a highly conductive BGE) with ESI-MS. [ABSTRACT FROM AUTHOR]

This year marks the 150th anniversary of the first continuous-flow chemistry (CFC) technique, developed by Ernest Solvay, which revolutionized industrial level synthesis. CFC is defined by multi-stage processes in which mixing and reacting of chemicals occur without interruption. A significant challenge of CFC lies in post-reaction purification. Free-flow electrophoresis (FFE) could be integrated with CFC. FFE separates chemicals by an electric field that is directed orthogonally to a pressure driven hydrodynamic flow. Although there are problems with FFE, both macro-scale and small-scale FFE are feasible for CFC integration, and realizing long-term steady-state continuous-flow purification can have significant benefits. In this review, we discuss (i) the progress of CFC, (ii) existing continuous-flow purification techniques, (iii) small-scale FFE limitations associated with steady-state continuous-flow purification, and (iv) advances in FFE performance. [ABSTRACT FROM AUTHOR]

Small-volume continuous-flow synthesis (small-vol- Conventional Device Optimized Device nme CFS) offers a number of benefits for use in small-scale chemical production and exploratory chemistry. Typically, small-volume CFS is followed by discontinuous purification; however, a fully continuous synthesis-purification combination is more attractive. Milli free-flow electrophoresis (mFFE) is a promising continuous-flow purification technique that is well suited for integration with small-volume CFS. The purification stability of mFFE, however, needs to be significantly improved before it can be feasible for this combination. One of the major sources of instability of mFFE is attributed to the ions produced as a result of electrolysis. These ions can form pH and conductivity gradients in mFFE, which are detrimental to separation quality. The severity of these gradients has not been thoroughly studied in mFFE. In this paper, we have experimentally demonstrated that detrimental pH gradients occur at flow rates of 8 mL/ min and less, and electric field strengths of 25 V/cm and greater. To decrease the pH gradients, it is necessary to evacuate H+ and OH- as soon as they are generated; this can be done by increasing local hydrodynamic flow rates. We calculated the necessary flow rate, to be applied at the electrode, which can effectively wash away both ions before they can cause a detrimental pH gradient These optimized flow rates can be attained by designing a device that incorporates deep channels. We have confirmed the effectiveness of these channels using a prototyped device. The new design allows mFFE users to work over a wider range of flow-rate and electric-field conditions without experiencing significant changes in pH. [ABSTRACT FROM AUTHOR]

Bubble and sweep: Free‐flow electrophoresis (FFE) could allow continuous‐flow purification of products from continuous‐flow microsynthesis. However, gas bubbles distort the separation. An open‐electrolyte FFE system avoids this problem. Electrodes placed in chimneys open to the atmosphere mean bubbles are vented directly from the system and cannot enter the separation channel (see picture). [ABSTRACT FROM AUTHOR]

Wie weggeblasen: Eine Free ‐ Flow ‐ Elektrophorese (FFE) könnte die kontinuierliche Produktaufreinigung in Strömungsmikrosynthesen ermöglichen, allerdings stören Gasbläschen den Trennprozess. Eine FFE ‐ System mit offenem Elektrolyten vermeidet dieses Problem. Entlüftungsschächte mit darin angebrachten Elektroden sorgen für die Entlüftung der Bläschen in die Atmosphäre, die auf diese Weise vom Trennungskanal ferngehalten werden (siehe Bild). [ABSTRACT FROM AUTHOR]