Scanning Electrochemical Microscopy of Electrically Heated Wire Substrates

We report a new configuration for enhancing the performance of scanning electrochemical microscopy (SECM) via heating of the substrate electrode. A flattened Pt microwire was employed as the substrate electrode. The substrate was heated by an alternating current (AC), resulting in an increased mass transfer between the wire surface and the bulk solution. The electrochemical response of the Pt wire during heating was investigated by means of cyclic voltammetry (CV). The open circuit potential (OCP) of the wire was recorded over time, while varied heating currents were applied to investigate the time needed for establishing steady-state conditions. Diffusion layer studies were carried out by performing probe approach curves (PACs) for various measuring modes of SECM. Finally, imaging studies of a heated substrate electrode surface, applying feedback, substrate generation/tip collection (SG/TC), and the competition mode of SECM, were performed and compared with room temperature results

Study of the response characteristics of an online electrochemical mass spectrometry system for gas analysis of lithium-ion cells using chronoamperometry

Online electrochemical mass spectrometry (OEMS) is a promising analytical technique to monitor minor side reactions with gaseous species, taking place while charging and discharging a lithium-ion cell. However, besides the manifold examples of these custom-made systems and their application, a clear analytical view on the origin of the evolving gasses and their manifold interactions within the cell environment is missing and therefore given in this work. To get a better understanding of the complexity of gas evolution associated with electrochemical reactions in lithium-ion cells, the use of chronoamperometry as an analytical method was chosen. This led to a precise variation of the applied voltage and voltage-pulse length and enabled therewith a clear starting point of the electrochemically triggered reactions. It was found that chronoamperometry can be used to precisely trigger those reactions with gaseous products. Additionally, it was found that the release of gaseous species depends on many parameters including the cell configuration, the current, and the gas species. The response time determination showed that a custom-made highly porous electrode configuration had an overall better response behavior within minutes with differences for the respective gasses of interest, compared to a standard foil configuration cells. The herein presented methodology shows how an electroanalytical approach can help gain further insight into advanced hyphenated methods, such as OEMS in the context of studies of lithium-ion cells

CE-UV/VIS and CE-MS for monitoring organic impurities during the downstream processing of fermentative-produced lactic acid from second-generation renewable feedstocks

During the downstream process of bio-based bulk chemicals, organic impurities, mostly residues from the fermentation process, must be separated to obtain a pure and ready-to-market chemical. In this study, capillary electrophoresis was investigated for the non-targeting downstream process monitoring of organic impurities and simultaneous quantitative detection of lactic acid during the purification process of fermentatively produced lactic acid. The downstream process incorporated 11 separation units, ranging from filtration, adsorption and ion exchange to electrodialysis and distillation, and 15 different second-generation renewable feedstocks were processed into lactic acid. The identification of organic impurities was established through spiking and the utilization of an advanced capillary electrophoresis mass spectrometry syste

Comparison of H2O2 screen-printed sensors with different Prussian blue nanoparticles as electrode material

In order to determine hydrogen peroxide condensing from gaseous and liquid phases screen-printed electrodes with controlled and adjustable thickness, shape and size of the working electrode as well as electrode paste composition were investigated. For this purpose Prussian blue (PB) nanoparticles with a different particle size distribution of 20- 30 nm (synthesized) and 60-100 nm (commercially available) were mixed with carbon paste and screen-printed on Al2O3 templates to establish H2O2-sensitive electrode. These two types of screen-printed sensors were compared to the commercial one during measurements in H2O2/water solutions at concentrations between 10-5 and 10-2 M H2O2. The linear signal in the investigated concentration range was found only for the sensor with the commercially available PB particles. Thus, this sensor prepared with PB particles of the size 60-100 nm showed the most reproducible and time-stable response versus the analyte in comparison to the others. This result offers the possibility to create sensors with adjustable design adapted to the concrete functionality. Thin films of collecting electrolytes based on agarose gels were printed on the sensor structures. They showed a distinct response on the application of H2O2-containing aerosols and gaseous phase

Dead volume–free flow splitting in capillary electrophoresis

In recent years, several dual detection concepts (DDCs) for CE were developed, which consisted of at least one nondestructive detector. For these DDCs, a linear detector arrangement could be used, which is not possible when both detectors are destructive. To overcome this problem, we developed a concept for the splitting of the CE stream utilizing commercially available flow splitters (FSs) that allow the parallel positioning of two destructive detectors. In this proof-of-concept study, T- and Y-shaped FSs were characterized regarding their suitability for DDCs. To keep it simple, a UV detector (UV) and a C4D were used for the characterization. The model system consisted of an acetonitrile-based background electrolyte and the two model substances, (ferrocenylmethyl)trimethylammonium iodide and caffeine. CE hyphenated to a UV detector (CE-UV) measurements revealed that the split ratio was about 50% for both FSs. CE-C4D was used to evaluate the peak shape in front of and behind the FSs. These measurements showed that there was no significant peak broadening introduced by the FSs. Additionally, there were no changes in the LODs in front of and behind the FSs. Furthermore, the flexibility of the new FS approach allowed the usage of capillaries with different ids (25–75 µm) for injection and detection

Determination of trimetazidine in urine by capillary electrophoresis with amperometric detection

In this contribution, nonaqueous capillary electrophoresis with end-column amperometric detection using a platinum ultramicroelectrode is presented along with several extraction procedures, both liquid–liquid extraction (LLE) and solid-phase extraction (SPE), for extracting trimetazidine from urine. Trimetazidine is an anti-ischemic drug, which changes hearth metabolism pathways and is being abused as a doping. Electrochemical detection in a nonaqueous environment provided a stable response with a relative standard deviation of only 3.6% (n = 10) in repeatability measurement at concentration of 50 µg cm−3. LOD and LOQ of the proposed method were determined as 0.054 µg cm−3 and 0.180 µg cm−3, respectively. From the point of view of LLE, the most efficient procedure was the double extraction with ethyl acetate as an extraction agent in combination with prior alkalinization of the sample by Na2CO3. Nevertheless, the extraction efficiency was only around 68%. The most efficient SPE procedure was based on the combination of HLB cartridge and elution with background electrolyte containing 20% of methanol. Its recovery reached up to 92% and 101% in case of 50 µg cm−3 and 5.0 µg cm−3 of trimetazidine in urine, respectively

Combining amperometry and mass spectrometry as a dual detection approach for capillary electrophoresis

Dual detection concepts (DDCs) are becoming more and more popular in analytical chemistry. In this work, we describe a novel DDC for capillary electrophoresis (CE) consisting of an amperometric detector (AD) and a mass spectrometer (MS). This detector combination has a good complementarity as the AD exhibits high sensitivity, whereas the MS provides excellent selectivity. Both detectors are based on a destructive detection principle, making a serial detector arrangement impossible. Thus, for the realization of the DDC, the CE flow was divided into two parts with a flow splitter. The DDC was characterized in a proof-of-concept study with ferrocene derivates and a nonaqueous background electrolyte. We could show that splitting the CE flow was a suitable method for the instrumental realization of the DDC consisting of two destructive detectors. By lowering the height of the AD compared to the MS, it was possible to synchronize the detector responses. Additionally, for the chosen model system, we confirmed that the AD was much more reproducible and had lower limits of detection (LODs) than the MS. The LODs were identical for the DDC and the single-detection arrangements, indicating no sensitivity decrease due to the CE flow splitting. The DDC was successfully applied to determine the drug and doping agent trimetazidine

Sensitive and selective determination of the neonicotinoid nitenpyram utilizing capillary electrophoresis hyphenated to amperometric detection/mass spectrometry

In this work, we present the sensitive and selective determination of the widely used insecticide nitenpyram (NIT), utilizing a newly developed dual detection concept (DDC) for capillary electrophoresis (CE). This DDC was realized by combining two complementary detection principles, namely amperometric detection (AD) and mass spectrometry (MS), using a commercially available flow splitter (CE-AD/MS). The novel DDC was implemented utilizing a newly developed, modular, and user-friendly CE system with a unique capillary positioning mechanism to improve the workflow. A detailed description of the CE device can be found in the Supporting Information. We investigated the analytical performance of the novel DDC (CE-AD/MS) in the context of NIT determination. The NIT LOD, obtained by AD, was up to a factor of 14 lower than in case of MS in the context of CE-AD/MS. The qualitative and quantitative determination of NIT in pharmaceutical samples is presented as a possible application for the novel DDC. Additionally, the oxidation process during AD was examined by hyphenation of electrochemistry to CE-MS

Signal enhancement in amperometric peroxide detection by using graphene materials with low number of defects

Two-dimensional carbon nanomaterials ranging from single-layer graphene to defective structures such as chemically reduced graphene oxide were studied with respect to their use in electrodes and sensors. Their electrochemical properties and utility in terms of fabrication of sensing devices are compared. Specifically, the electrodes have been applied to reductive amperometric determination of hydrogen peroxide. Low-defect graphene (SG) was obtained through mechanical exfoliation of natural graphite, while higher-defect graphenes were produced by chemical vapor deposition (CVDG) and by chemical oxidation of graphite and subsequent reduction (rGO). The carbonaceous materials were mainly characterized by Raman microscopy. They were applied as electrode material and the electrochemical behavior was investigated by chronocoulometry, cyclic voltammetry, electrochemical impedance spectroscopy and amperometry and compared to a carbon disc electrode. It is shown that the quality of the graphene has an enormous impact on the amperometric performance. The use of carbon materials with many defects (like rGO) does not result in a significant improvement in signal compared to a plain carbon disc electrode. The sensitivity is 173 mA center dot M-1 center dot cm(-2) in case of using CVDG which is about 50 times better than that of a plain carbon disc electrode and about 7 times better than that of rGO. The limit of detection for hydrogen peroxide is 15.1 mu M (at a working potential of -0.3 V vs SCE) for CVDG. It is concluded that the application of two-dimensional carbon nanomaterials offers large perspectives in amperometric detection systems due to electrocatalytic effects that result in highly sensitive detection