State-of-the-art electrochemical and optical sensors present distinct advantages and disadvantages when used individually. Combining both methodologies offers interesting synergies and makes it possible to exploit strengths and circumvent possible problems of the individual methods. We report a dynamic sensing concept for buffer capacity by applying water electrolysis to modulate the pH microenvironment in front of an optical pH sensor placed in a flow cell. Using this combinatory approach in a nonequilibrium readout mode allowed us to assess the concentration of different buffer species in relatively short time (1 min per measurement). Theoretical simulations of the system were performed to validate the presented method. Additionally, the dynamic measurement approach enabled in situ determination of the apparent pK a of MOPS (3-(N-morpholino)propanesulfonic acid) buffer at ambient conditions. The dynamic and combinatory approach presented here holds large potential also for other pH-active analytes.
The oxygen transfer rate (OTR) of dioxygen to solutions describing the transport of oxygen gas from the gaseous phase into the liquid phase of a reaction system over a given period is an important measure for biotechnological applications. The OTRs have already been described for aqueous systems and also recently for organic and non-conventional media, whereas the OTRs of a novel class of solvents, deep eutectic solvents (DESs), have not been determined yet. In this contribution, we report for the first time on the OTRs of choline chloride:ethylene glycol (ChCl:EG, 'ethaline') and ethylammonium chloride:ethylene glycol (EAC:EG, 'ethethylaline') while using water as a reference. We applied the dynamic measurement method and found up to 11-fold lower volumetric mass transfer coefficient (kLa) for ethaline and 6-fold lower for ethethylaline when compared to water at 25°C. Furthermore, we investigated the effect temperature (35°C and 45°C) has on the kLa for those solvents. File list (2) download file view on ChemRxiv 2021-03-03_ChemRxiv_Manuscript.pdf (508.61 KiB) download file view on ChemRxiv 2021-03-03_ChemRxiv_SuppInfo.pdf (664.82 KiB) Can deep eutectic solvents sustain oxygen dependent bioprocesses? -Measurements of oxygen transfer rates
We present a dipping probe total dissolved inorganic carbon (DIC) microsensor based on a localized acidic microenvironment in front of an amperometric CO 2 microsensor. The acidic milieu facilitates conversion of bicarbonate and carbonate to CO 2 , which in turn is reduced at a silver cathode. Interfering oxygen is removed by an acidic CrCl 2 oxygen trap. Theoretical simulations of microsensor functioning were performed to find a suitable compromise between response time and near-complete conversion of bicarbonate to CO 2 . The sensor exhibited a linear response over a wide range of 0−8 mM DIC, with a calculated LOD of 5 μM and a 90% response time of 150 s. The sensor was successfully tested in measuring DIC in bottled mineral water and seawater. This DIC microsensor holds the potential to become an important tool in environmental sensing and beyond for measurements of DIC at high spatial and temporal resolution.
In this letter, we demonstrate 2D acidification of samples at environmental and physiological pH with an electrochemically activated polyaniline (PANI) mesh. A novel sensor–actuator concept is conceived for such a purpose. The sample is sandwiched between the PANI (actuator) and a planar pH optode (sensor) placed at a very close distance (∼0.50 mm). Upon application of a mild potential to the mesh, in contrast to previously reported acidification approaches, PANI releases a significant number of protons, causing an acid–base titration in the sample. This process is monitored in time and space by the pH optode, providing chemical imaging of the pH decrease along the dynamic titration via photographic acquisition. Acidification of samples at varying buffer capacity has been investigated: the higher the buffer capacity, the more time (and therefore proton charge) was needed to reach a pH of 4.5 or even lower. Also, the ability to map spatial differences in buffer capacity within a sample during the acid–base titration was unprecedentedly proven. The sensor–actuator concept could be used for monitoring certain analytes in samples that specifically require acidification pretreatment. Particularly, in combination with different optodes, dynamic mapping of concentration gradients will be accessible in complex environmental samples ranging from roots and sediments to bacterial aggregates.
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