Electrochemical Flow-through Cell Research Articles

Development of a 3D Ni-Mn binary oxide anode for energy-efficient electro-oxidation of organic pollutants

The depletion of clean water resources and the consequent accumulation of contaminants in aquatic systems must be urgently addressed by means of innovative solutions. Electro-oxidation (EO) is considered a promising technology, prized for its versatility and eco-friendliness. However, the excessively high prices and the toxicity associated with some of the materials currently employed for EO impede its broader application. This study introduces cost-effective Ni-Mn binary oxide anodes prepared on Ni foam (NF) substrate. A scalable synthesis route that enables a 35-fold increase in the production of active material through a single optimization step has been devised. The synthesized binary oxide material underwent electrochemical characterization, and its effectiveness was assessed in an electrochemical flow-through cell, benchmarked against single Ni or Mn oxides and more conventional alternatives like boron-doped diamond (BDD) and dimensionally-stable anode (DSA). The novel binary oxide anode demonstrated exceptional performance, achieving complete removal of phenol at very low current density of 5 mA cm−2, along with an 80% of chemical oxygen demand (COD) decay within only 60 min. The NF/NiMnO3 anode outperformed the BDD and DSA when using comparable projected surface areas, owing to its high porosity and ability to produce hydroxyl radicals, as confirmed from the degradation profiles in the presence of radical scavengers. Furthermore, GC/MS analysis served to elucidate the degradation pathways of phenol.

Development of an electrochemical flow-through cell for the fast and easy generation of isotopically labeled metabolite standards.

In drug development, metabolite standards of new chemical entities are required for a comprehensive safety evaluation. Stable isotope-labeled internal metabolite standards at the milligram scale, which are difficult and expensive to synthesize in common bottom-up approaches, are necessary for metabolite quantification using liquid chromatography/mass spectrometry. A preparative electrochemical flow-through cell is presented here as a powerful tool for the cheap and straightforward synthesis of milligram amounts of isotopically labeled metabolite standards. The developed cell scales up established, so-called "coulometric" electrochemical cells. Problems like electrode fouling and cross contamination between syntheses are addressed by the use of exchangeable working electrodes. The applicability of the developed cell for the synthesis of metabolite standards is demonstrated using isotopically labeled acetaminophen as a model system for the generation of a biologically relevant phase II metabolite.

Mass-Spectrometric Imaging of Electrode Surfaces-a View on Electrochemical Side Reactions.

Electrochemical side reactions, often referred to as “electrode fouling”, are known to be a major challenge in electro‐organic synthesis and the functionality of modern batteries. Often, polymerization of one or more components is observed. When reaching their limit of solubility, those polymers tend to adsorb on the surface of the electrode, resulting in a passivation of the respective electrode area, which may impact electrochemical performance. Here, matrix‐assisted laser‐desorption/ionization mass spectrometry (MALDI‐MS) is presented as valuable imaging technique to visualize polymer deposition on electrode surfaces. Oligomer size distribution and its dependency on the contact time were imaged on a boron‐doped diamond (BDD) anode of an electrochemical flow‐through cell. The approach allows to detect weak spots, where electrode fouling may take place and provides insight into the identity of side‐product pathways.

Using electrochemistry coupled to high resolution mass spectrometry for the simulation of the environmental degradation of the recalcitrant fungicide carbendazim

Currently, there is a growing interest in the study of environmental degradation pathways of organic contaminants such as pesticides, with the objective to better understand their potential risk for environmental systems and living organisms. In this context, DFT (conceptual density functional theory) and predictive methods may systematically be used to simplify and accelerate the elucidation of environmental degradation. We report herein the electrochemical behavior/degradation of the carbendazim (CBZ) fungicide widely used to treat cereal and fruit crops. Oxidative degradation of CBZ was studied using an electrochemical flow-through cell directly coupled to a mass spectrometer for rapid identification of CBZ degradation products. The structural elucidation of CBZ oxidation products was based on retention time, accurate mass, isotopic distribution and fragmentation pattern by using LC-HRMS an LC-HRMS2. The most important chemical reactions found to occur in the transformation of CBZ were hydrolysis and hydroxylation. EC-LC-MS and EC-MS analysis has made it possible to highlight the identification of degradation products of CBZ. In addition to previously known transformation products common to those observed during environmental degradation (monocarbomethoxyguanidine, benzimidazole-isocyanate, 2-aminobenzimidazole, hydroxy-2-aminobenzimidazole, hydroxycarbendazim, CBZ-CBZ dimer), two new degradation products were identified in this work: a quinone imine and a nitrenium ion. Electrochemistry mass spectrometry hyphenated techniques represent an accessible, rapid and reliable tool to elucidate the oxidative degradation of CBZ, including reactive degradation products and conjugates.

An Electrochemical Flow-Through Cell for Rapid Reactions

Here, we report the design and application of an electrochemical flow cell that provides excellent mixing and enables high current densities on research-relevant scales (≤1 g, up to 10 g scale). Th...

Novel Electrochemical Flow Injection Procedure for Albendazole Determination using Boron-doped Diamond thin Film Electrode

The homemade electrochemical cell for electrochemical determination of albendazole using boron-doped diamond (BDD) thin film electrode is developed. Electrochemical activity of albendazole was investigated by cyclic voltammetry in 0.10 M phosphate buffer containing 20% (v/v) methanol at pH 2.5. Using the BDD electrode well-defined and highly reproducible cyclic voltammogram was obtained with current signal-to-background ratio of higher than those obtained from the glassy carbon electrode. Flow injection analysis system with amperometric detection using the homemade thin-layer electrochemical flow-through cell with BDD electrode was studied. The hydrodynamic voltammogram of the drug exhibited single well defined maximum oxidation peak at 0.95 V versus Ag/AgCl. A low detection limit of 2 ppm was obtained. The current–concentration relationship was rectilinear over the concentration range of 3.3‒150 ppm. The proposed method was applied to albendazole tablets with satisfactory results.

Rates of H2O2 electrogeneration by reduction of anodic O2 at RVC foam cathodes in batch and flow-through cells

The Electro-Fenton process for in-situ H2O2 electrogeneration is impacted by low O2 utilization efficiency (<0.1%) and the need of acid for pH adjustment. An electrochemical flow-through cell can develop localized acidic conditions, coupled with simultaneous formation and utilization of O2 to enhance H2O2 formation. Multiple electrode configurations using reticulated vitreous carbon (RVC) foam and Ti/mixed metal oxides (MMO) are proposed to identify the optimum conditions for H2O2 formation in batch and flow-through cells. A pH of 2.75 ± 0.25 is developed locally in the flow-through cell that supports effective O2 reduction. Up to 9.66 mg/L H2O2 is generated in a 180 mL batch cell under 100 mA, at pH 2, and mixing at 350 rpm. In flow-through conditions, both flow rate and current significantly influence H2O2 production. A current of 120 mA produced 2.27 mg/L H2O2 under a flow rate of 3 mL/min in a 3-electrode cell with one RVC foam cathode at 60 min. The low current of 60 mA does not enable effective H2O2 production, while the high current of 250 mA produced less H2O2 due to parasitic reactions competing with O2 reduction. Higher flow rates decrease the retention time, but also increase the O2 mass transfer. Furthermore, 3-electrode flow-through cell with two RVC foam cathodes was not effective for H2O2 production due to the limited O2 supply for the secondary cathode. Finally, a coupled process that uses both O2 and H2 from water electrolysis is proposed to improve the H2O2 yield further.

P 130 - Oxidative metabolism of phosphatidylethanolamines predicted by electrochemistry-mass spectrometry

Phosphatidylethanolamines (PEs) are a major class of phospholipids in cellular membranes and lipoproteins. Oxidation of PEs generates products exerting a vast number of biological functions, not totally unveiled yet. In vitro biomimetic models have been used to identify oxidized PEs and to develop analytical strategies for their targeted in vivo detection. Most models are based on radical oxidation, but the oxidative metabolism of PE also relies on controlled reactions catalyzed by enzymes as lipoxygenase (LOX), which can be mimicked by electrochemical (EC) oxidation. In this study, three PE standards were oxidized using an EC flow-through cell as a biomimetic model of oxidative injury. The oxidation products were identified by on-line EC-electrospray ionization mass spectrometry (ESI-MS and MS/MS). Long chain and short chain oxidation products were identified as modifications in the sn-2 acyl chain, whereas the oxidation pattern was dependent on the unsaturation level. Some of these oxidized species have already been observed during the modification of PEs driven by radical oxygen species (ROS), and among these products it was possible to characterize the oxidized isomers synthesized by 15-LOX in human immune cells. This EC-MS platform was, therefore, able to mimic the oxidative metabolism of PEs mediated by both ROS and enzymes.

Inorganic arsenic speciation in natural mineral drinking waters by flow-through anodic stripping chronopotentiometry

A simple and inexpensive method for chemical speciation of inorganic As in natural mineral drinking waters by using anodic stripping chronopotentiometry (ASCP) in an electrochemical flow-through cell with an Au wire as the working electrode was described in the present work. The presented method is an attractive alternative to laborious and time-consuming procedures requiring pre-separation of various forms of As before their detection by other flow-through and non flow-through stripping methods. The limits of detection were found to be 0.42µgL−1 for As(III) and 0.55µgL−1 for As(V), obtained at the deposition potentials of −350mV and −1600mV, respectively. The accuracy of the method was assessed by the spiking-and-recovery experiments for particular water samples and the recoveries found, being in range from 99% to 105% for As(III) and from 104% to 106% for As(V), respectively, were quantitative. The proposed method was successfully applied to speciation analysis of inorganic As in water samples with a high content of Cu.

Electrochemical oxidative dimerization of monobrominated phenols and pentabromophenol in methanol-aqueous media

The electrochemical oxidation of monobrominated phenols (2-bromophenol, 3-bromophenol, 4-bromophenol) and pentabromophenol in methanol-aqueous solutions (1:1 and 9:1, v/v) was studied by cyclic voltammetry on glassy carbon electrode in static and rotating disc arrangement. First oxidation step was followed by dimerization reaction resulting in formation of electroactive species. Products of controlled potential electrolysis of bromophenols on the platinum gauze electrode were analysed by ultra-performance liquid chromatography/time of flight mass spectrometry and by gas chromatography/mass spectrometry. C–C and C–O–C linked dimers were found as the main oxidation products in monobrominated phenols solutions electrolysed under mild conditions. Pentabromophenol provided a dimer with C–O–C linkage. On-line coupling of mass spectrometry with electrochemical flow-through cell (EC/MS) containing platinum working electrode proved formation of dimers in the case of 2-bromophenol and 4-bromphenol.

Highly sensitive electrochemiluminescence determination of etamsylate using a low‐cost electrochemical flow‐through cell based on a tris(2, 2'‐bipyridyl)ruthenium(II)–Nafion‐modified carbon paste electrode

A simple and sensitive electrochemiluminescence (ECL) method for the determination of etamsylate has been developed by coupling an electrochemical flow-through cell with a tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+))-Nafion-modified carbon electrode. It is based on the oxidized Ru(bpy)3(2+) on the electrode surface reacting with etamsylate and producing an excellent ECL signal. Under optimized experimental conditions, the proposed method allows the measurement of etamsylate over the range of 8-1000 ng/mL with a correlation coefficient of r = 0.9997 (n = 7) and a limit of detection of 1.57 ng/mL (3σ), the relative standard deviation (RSD) for 1000 ng/mL etamsylate (n = 7) is 0.96%. The immobilized Ru(bpy)3(2+) carbon paste electrode shows good electrochemical and photochemical stability. This method is rapid, simple, sensitive and has good reproducibility. It has been successfully applied to the determination of the studied etamsylate in pharmaceutical preparations with satisfactory results. The possible ECL reaction mechanism has also been discussed.

Neutron imaging of ion transport in mesoporous carbon materials

Neutron imaging is presented as a tool for quantifying the diffusion of ions inside porous materials, such as carbon electrodes used in the desalination process via capacitive deionization and in electrochemical energy-storage devices. Monolithic mesoporous carbon electrodes of ∼10 nm pore size were synthesized based on a soft-template method. The electrodes were used with an aqueous solution of gadolinium nitrate in an electrochemical flow-through cell designed for neutron imaging studies. Sequences of neutron images were obtained under various conditions of applied potential between the electrodes. The images revealed information on the direction and magnitude of ion transport within the electrodes. From the time-dependent concentration profiles inside the electrodes, the average value of the effective diffusion coefficient for gadolinium ions was estimated to be 2.09 ± 0.17 × 10(-11) m(2) s(-1) at 0 V and 1.42 ± 0.06 × 10(-10) m(2) s(-1) at 1.2 V. The values of the effective diffusion coefficient obtained from neutron imaging experiments can be used to evaluate model predictions of the ion transport rate in capacitive deionization and electrochemical energy-storage devices.

Highly Sensitive Determination of Cadmium and Lead Using a Low-cost Electrochemical Flow-through Cell Based on a Carbon Paste Electrode

A low-cost thin-layer electrochemical flow-through cell based on a carbon paste electrode (CPE), was constructed for the highly sensitive determination of cadmium(II) (Cd(2+)) and lead(II) (Pb(2+)) ions. The sensitivity of the proposed cell for Cd(2+) and Pb(2+) ion detection was improved by using the smallest channel height without the need for any complicated electrode modification. Under the optimum conditions, the detection limits of Cd(2+) and Pb(2+) ions (0.08 and 0.07 µg dm(-3), respectively) were 13.8- and 11.4-fold lower than that of a commercial flow cell (1.1 and 0.8 µg dm(-3), respectively). Moreover, the percentage recoveries of Cd(2+) and Pb(2+) for the in-house designed thin-layer flow cell were higher than those for the commercially available cell in all tested water samples, and within the acceptable range. The proposed flow cell is promising as an inexpensive and alternative one for the highly sensitive monitoring of heavy metal ions.

A ferrocene-based reagent for the conjugation and quantification of reactive metabolites

In the present study, a method for the analysis of reactive metabolites via liquid chromatography (LC) with inductively coupled plasma-mass spectrometry (MS) was developed. A ferrocenyl-modified glutathione (GSH) reagent, consisting of GSH and succinimidyl-3-ferrocenylpropionate, was synthesized. Derivatization of the tripeptide was performed at the N-terminus, leaving the nucleophilic thiol group vacant for the attack of electrophilic compounds. The potential of ferrocenylpropionate (FP)-GSH as a trapping agent for reactive metabolites was investigated using an electrochemical flow-through cell for metabolism simulation coupled online to a LC system with electrospray ionization mass spectrometric detection. The pharmaceuticals amodiaquine, an antimalarial agent, and clozapine, an antipsychotic compound, served as model substances. By proving the successful adduct formation between the reactive metabolite and ferrocene-labeled GSH, it could be shown that FP-GSH is an effective trapping agent which eases routine reversed-phase LC analyses. In contrast to GSH, which is usually used for the conjugation of reactive metabolites and where the resulting adducts often show no or only very little retention, FP-GSH facilitates the detection of the corresponding metabolite adducts due to higher retention times.

Adsorption and Desorption Kinetics of a Block Copolymer Wetting Agent Used in Copper Electroplating

Current development of copper electroplating additives has led to the development of suppressors that not only allow for proper bottom-up fill but also that wet the surface properly for defect-free entry of the copper-seeded wafer into the plating bath. The current work analyzes the adsorption and desorption characteristics of a common block copolymer wetting agent using an electrochemical flow-through cell. Adsorption characteristics are similar to that of polyethylene glycol (PEG) during electroplating, where the adsorption process becomes a strong function of polymer bulk concentration under and where increasing applied potential or current causes the surface suppression of the polymer to decrease. Desorption experiments showed similar results to PEG as well, where a two-stage desorption is seen when the applied potential or current becomes large enough. Computation fluid dynamic modeling of the flow-through cell allowed for the determination of the saturated surface coverage at vs , which was . Additionally, the adsorption rate constant was modeled to be 6.02, 2.045, and for applied potentials of , , and vs , assuming a constant saturated surface coverage of .

Electrochemistry meets enzymes: instrumental on-line simulation of oxidative and conjugative metabolism reactions of toremifene

The metabolism of the selective estrogen receptor modulator toremifene was simulated in an on-line electrochemistry/enzyme reactor/liquid chromatography/mass spectrometry system. To simulate the oxidative phase I metabolism, toremifene was oxidized in an electrochemical (EC) flow-through cell at 1,500 mV vs. Pd/H2 to its phase I metabolites, some of which are reactive quinoid species. In the presence of glutathione-S-transferase (GST), these quinoid compounds react with glutathione, which is also the common detoxification mechanism in the body. While reacting with glutathione, the chlorine atom is eliminated from the toremifene moiety. Due to higher conversion rates, GST supplied in continuous flow proved to be more efficient than using immobilized GST on magnetic microparticles. In the absence of GST, not all GSH adducts are formed, proving the necessity of a phase II enzyme to simulate the complete metabolic pathway of xenobiotics in an on-line EC/LC/MS system.

Quantification of Electrochemically Generated Iodine-Containing Metabolites Using Inductively Coupled Plasma Mass Spectrometry

For the risk assessment of drug candidates, the identification and quantification of their metabolites is required. The majority of analytical techniques is based on calibration standards for quantification of the metabolites. As these often are not readily available, the use of inductively coupled plasma mass spectrometry (ICPMS) is an attractive alternative for drugs containing heteroatoms. In this work, the online coupling of electrochemistry (EC), liquid chromatography (LC), and ICPMS is presented. The antiarrhythmic agent amiodarone, which contains two iodine atoms, is oxidized in an electrochemical flow-through cell under N-dealkylation and deiodination. The metabolites that are generated at different EC potentials are identified by electrospray ionization (ESI) mass spectrometry, compared to those from rat liver microsomal incubations and quantified by ICPMS. Phase-optimized LC, a recent approach for high-performance isocratic separations, is used to avoid the ICPMS calibration problems known to occur with gradient separations. The potential of the complementary use of ESI-MS and ICPMS for the qualitative and quantitative analysis of drug metabolites becomes apparent in this work.

Covalent Protein Modification by Reactive Drug Metabolites Using Online Electrochemistry/Liquid Chromatography/Mass Spectrometry

We present a rapid and convenient method to perform and evaluate the covalent protein binding of reactive phase I metabolites. The oxidative metabolism of the drugs paracetamol, amodiaquine, and clozapine is simulated in an electrochemical (EC) flow-through cell, which is coupled online to an LC/MS system. Adduct formation of the reactive metabolites with the proteins beta-lactoglobulin A and human serum albumin proceeds in a reaction coil between EC cell and injection system of the HPLC system. The formed drug-protein adducts are characterized with online time-of-flight mass spectrometry, and the modification site is localized using FTICR-mass spectrometry. Due to its simple setup, easy handling, and short analysis times, the method provides an interesting tool for the rapid risk assessment of covalent protein binding as well as for the synthesis of covalent drug-protein adducts in high purity and high yield.

Simultaneous LC/MS/MS Determination of Thiols and Disulfides in Urine Samples Based on Differential Labeling with Ferrocene-Based Maleimides

A method for the simultaneous determination of a series of thiols and disulfides in urine samples has been developed based on the sequential labeling of free and bound thiol functionalities with two ferrocene-based maleimide reagents. The sample is first exposed to N-(2-ferroceneethyl)maleimide, thus leading to the derivatization of free thiol groups in the sample. After quantitative reaction and subsequent reduction of the disulfide-bound thiols by tris(2-carboxyethyl)phosphine, the newly formed thiol functionalities are reacted with ferrocenecarboxylic acid-(2-maleimidoyl)ethylamide. The reaction products are determined by LC/MS/MS in the multiple reaction mode, and precursor ion scan as well as neutral loss scan is applied to detect unknown further thiols. The method was successfully applied to the analysis of free and disulfide-bound thiols in urine samples. Limits of detection are 30 to 110 nM, and the linear range comprises two decades of concentration, thus covering the relevant concentration range of thiols in urine samples. The thiol and disulfide concentrations were referred to the creatinine content to compensate for different sample volumes. As some calibration standards for the disulfides are not commercially available, they were synthesized in an electrochemical flow-through cell. This allowed the synthesis of hetero- and homodimeric disulfides.

Simulation of the detoxification of paracetamol using on-line electrochemistry/liquid chromatography/mass spectrometry

On-line electrochemistry/liquid chromatography/mass spectrometry was used to simulate the detoxification mechanism of paracetamol in the body. In an electrochemical flow-through cell, paracetamol was oxidized at a porous glassy carbon working electrode at a potential of 600 mV vs. Pd/H2 with formation of a quinoneimine intermediate. The quinoneimine further reacted with glutathione and/or N-acetylcysteine to form isomeric adducts via the thiol function. The adducts were characterized on-line by liquid chromatography/mass spectrometry. These reactions are similar to those occurring between paracetamol and glutathione under catalysis by cytochrome P450 enzymes in the body.