Standard Three-electrode Configuration Research Articles

Classification and prediction of rice wines with different marked ages by using a voltammetric electronic tongue

A voltammetric electronic tongue (VE-tongue) was developed to discriminate the difference between Chinese rice wines in this research. Three types of Chinese rice wine with different marked ages (1, 3, and 5 years) were classified by the VE-tongue by principal component analysis (PCA) and cluster analysis (CA). The VE-tongue consisted of six working electrodes (gold, silver, platinum, palladium, tungsten, and titanium) in a standard three-electrode configuration. The multi-frequency large amplitude pulse voltammetry (MLAPV), which consisted of four segments of 1 Hz, 10 Hz, 100 Hz, and 1000 Hz, was applied as the potential waveform. The three types of Chinese rice wine could be classified accurately by PCA and CA, and some interesting regularity is shown in the score plots with the help of PCA. Two regression models, partial least squares (PLS) and back-error propagation-artificial neural network (BP–ANN), were used for wine age prediction. The regression results showed that the marked ages of the three types of Chinese rice wine were successfully predicted using PLS and BP–ANN.

Classification of monofloral honeys by voltammetric electronic tongue with chemometrics method

A voltammetric electronic tongue (VE-tongue) based on multifrequency large amplitude pulse voltammetry (MLAPV) was developed to classify monofloral honeys of seven kinds of floral origins. The VE-tongue was composed of six working electrodes (gold, silver, platinum, palladium, tungsten, and titanium) in a standard three-electrode configuration. The applied waveform of MLAPV was composed of four individual frequencies: 1 Hz, 10 Hz, 100 Hz, and 1000 Hz. Two eigenvalues (the maximum value and the minimum value) of each cycle were extracted for building the first database (FDB); four eigenvalues (the maximum value, the minimum value, and two inflexion values) were exacted for building the second database (SDB). The two databases were analyzed by three-pattern recognition techniques: principal component analysis (PCA), discriminant function analysis (DFA) and cluster analysis (CA), respectively. It was possible to discriminate the seven kinds of honeys of different floral origins completely based on FDB and SDB by PCA, DFA and CA, and FDB was certificated as an efficient database by contrasting with the SDB. Moreover, the effective working electrodes and frequencies were picked out as the best experimental project for the further study.

Detection of antibiotic residues in bovine milk by a voltammetric electronic tongue system

A voltammetric electronic tongue (VE-tongue) was developed to detect antibiotic residues in bovine milk. Six antibiotics (Chloramphenicol, Erythromycin, Kanamycin sulfate, Neomycin sulfate, Streptomycin sulfate and Tetracycline HCl) spiked at four different concentration levels (0.5, 1, 1.5 and 2 maximum residue limits (MRLs)) were classified based on VE-tongue by two pattern recognition methods: principal component analysis (PCA) and discriminant function analysis (DFA). The VE-tongue was composed of five working electrodes (gold, silver, platinum, palladium, and titanium) positioned in a standard three-electrode configuration. The Multi-frequency large amplitude pulse voltammetry (MLAPV) which consisted of four segments (1 Hz, 10 Hz, 100 Hz and 1000 Hz) was applied as potential waveform. The six antibiotics at the MRLs could not be separated from bovine milk completely by PCA, but all the samples were demarcated clearly by DFA. Three regression models: Principal Component Regression Analysis (PCR), Partial Least Squares Regression (PLSR), and Least Squares-Support Vector Machines (LS-SVM) were used for concentrations of antibiotics prediction. All the regression models performed well, and PCR had the most stable results.

Counter-Electrode-Free Thin Cu Film Deposition Based on Ballistic Electron Injection into CuSO4 Solution from Nanosilicon Emitter

It is shown that a nanocrystalline silicon (nc-Si) ballistic electron emitter acts as an active electrode in a metal–salt solution (such as CuSO4 solution). The nc-Si emitter is composed of a thin Au film (10 nm thick), anodized polycrystalline layer (1 µm thick), and single-crystalline n+-Si substrate. In accordance with the results of an analysis by cyclic-voltammogram measurements under the standard three-electrode configuration, the electron injection effect into the solution is clearly observed at a potential within the electrochemical window where no electrolytic reactions appear. When the nc-Si emitter is driven alone in a CuSO4 solution without using any counter electrodes, a polycrystalline thin Cu film is uniformly formed on the emitting surface. This is presumably due to the preferential reduction of Cu2+ ions at the interface by injected energetic electrons. The observed deposition mode is different from both the conventional electroplating and electroless plating. This technique is an alternative low-temperature wet process that will be applicable to the deposition of various thin metal films.

Classification and prediction of Chinese rice wines with different marked ages by using a voltammetric electronic tongue

A voltammetric electronic tongue (VE-tongue) was developed to discriminate the difference between Chinese rice wines in this research. Three types of Chinese rice wines with different marked ages (1, 3 and 5 years) were classified based on VE-tongue by Principal component analysis (PCA), Cluster analysis (CA). The VE-tongue consisted of six working electrodes (gold, silver, platinum, palladium, tungsten, and titanium) in a standard three-electrode configuration. The Multi-frequency large amplitude pulse voltammetry (MLAPV) which consisted of four segments of 1 Hz, 10 Hz, 100 Hz and 1000 Hz was applied as potential waveform. Three types of Chinese rice wines could be classified completely by PCA and CA, and some interesting regularity is shown in the score plots with the help of PCA. Two regression models: Partial Least Squares (PLS) and Back-error propagation–Artificial neural network (BP–ANN) were used for wine age prediction. The regression analysis showed that the marked ages of the three types of Chinese rice wine were successfully predicted by PLS and BP–ANN.

Differentiation of four Aspergillus species and one Zygosaccharomyces with two electronic tongues based on different measurement techniques

Two electronic tongues based on different measurement techniques were applied to the discrimination of four molds and one yeast. Chosen microorganisms were different species of Aspergillus and yeast specie Zygosaccharomyces bailii, which are known as food contaminants. The electronic tongue developed in Linköping University was based on voltammetry. Four working electrodes made of noble metals were used in a standard three-electrode configuration in this case. The St. Petersburg electronic tongue consisted of 27 potentiometric chemical sensors with enhanced cross-sensitivity. Sensors with chalcogenide glass and plasticized PVC membranes were used. Two sets of samples were measured using both electronic tongues. Firstly, broths were measured in which either one of the molds or the yeast grew until late logarithmic phase or border of the stationary phase. Broths inoculated by either one of molds or the yeast was measured at five different times during microorganism growth. Data were evaluated using principal component analysis (PCA), partial least square regression (PLS) and linear discriminant analysis (LDA). It was found that both measurement techniques could differentiate between fungi species. Merged data from both electronic tongues improved differentiation of the samples in selected cases.

Use of an electronic tongue and HPLC with electrochemical detection to differentiate molds in culture media

A study was conducted to further evaluate an electronic tongue, using high-performance liquid chromatography (HPLC) with electrochemical (EC) and UV detection as a reference method. The electronic tongue consisted of four working electrodes made of different metals and arranged in a standard three-electrode configuration. Pulses of voltage were applied to the metals, and the current responses were sampled and collected in a data matrix. The objectives of the present investigation were to examine the ability of the electronic tongue to distinguish between two mold species growing in three different media, and to obtain support for the hypothesis that the device actually discriminates between different redox-active metabolites produced by the molds. Peak areas in EC and UV HPLC chromatograms were collected in a data matrix. The electronic tongue data and the EC and UV data were then subjected to principal component analysis (PCA). A number of peaks in the HPLC–EC chromatograms indicated that the growth media contained redox-active metabolites. Moreover, PCA of peak areas in EC chromatograms revealed differences between the distribution of redox-active metabolites produced by the two species and between the three culture media. The same pattern was apparent in a PCA score plot of electronic tongue data. The peaks in the UV and EC chromatograms differed, and these were also shown by the PCA score plots.

Infrared spectroscopic studies on Mg intercalated crystalline MoO3 thin films

MoO3 thin films were intercalated with Mg ions using a standard three-electrode configuration. The concentration of Mg ions was varied from x=0.05 to x=0.4, where x is the ratio of Mg ions and host Mo ions. IR studies were carried out on unintercalated, intercalated, deintercalated and aged films. The effect of ion concentration (x) on lattice distortion and reversibility has been investigated by monitoring systematically the number of resonance absorption peaks, their respective intensities and spectral locations. At low values of x (<0.2) the lattice expansion along b-axis was observed and beyond which lattice distortion along a-axis was seen. The presence of characteristic resonance absorption peaks at 988, 808 and 537cm−1 confirms formation of layered orthorhombic MoO3 phase. IR studies of deintercalated films confirm that the chemical changes occurring at terminal double bonds are irreversible while these are reversible at other sites. The stability of intercalated films was investigated by monitoring the IR reflectance time to time after exposing them to ambience. No measurable degradation was observed even after 6 months.

Capillary electrophoresis coupled with electrochemiluminescence detection using porous etched joint.

A new setup to couple capillary electrophoresis (CE) with electrochemiluminescence (ECL) detection is described in which the electrical connection of CE is achieved through a porous section at a distance of 7 mm from the CE capillary outlet. Because the porous capillary wall allowed the CE current to pass through and there was no electric field gradient beyond that section, the influence of CE high-voltage field on the ECL procedure was eliminated. The porous section formed by etching the capillary with hydrofluoric acid after only one side of the circumference of 2-3 mm of polyimide coating of the capillary was removed, while keeping the polyimide coating on the other part to protect the capillary from HF etching makes the capillary joint much more robust since only a part of the circumference of it is etched. A standard three-electrode configuration was used in experiments with Pt wire as a counter electrode, Ag/AgCl as a reference electrode, and a 300-microm diameter Pt disk as a working electrode. Compared with CE-ECL conventional decoupler designs, the present setup with a porous joint has no added dead volume created. Moreover, the dead volume can be increasingly decreased by shortening the distance ( approximately 100 microm) between the working electrode and the end of the separation capillary. The versatility in choice of capillaries and separation buffers within this design is the main advantage over the use of small i.d. capillary and low conductivity buffer in some CE-ECL systems. The performance of this setup is illustrated by the analyses of tripropylamine and proline.

Infrared and electrochemical studies on Mg intercalated a-MoO 3 thin films

MoO 3 thin films were intercalated with Mg ions using a standard three-electrode configuration. The concentration of Mg ions was varied from x=0.1 to x=0.7, where x is the ratio of intercalated Mg ions and host Mo ions. Infrared (IR) studies were carried out on intercalated and deintercalated films. The effect of Mg ion concentration on the nature of interaction with host ions and cyclability has been investigated by monitoring selected resonance absorption peaks' intensities and spectral locations. The intensities of few characteristic absorption peaks were very sensitive to humidity confirming adsorption of water vapor. The diffusivity ( D) of Mg ions has been estimated from Galvanostatic Intermittent Titration Technique (GITT) and the same is correlated with the chemical changes occurring in the films on intercalation. The estimated D values are of the order of 10 −17–10 −18 cm 2/s. The D value is found to be a strong function of number of intercalation/deintercalation cycle. The IR spectrum of deintercalated film, cycled five times, provides evidence of residual ions in the films.

Monitoring of freshness of milk by an electronic tongue on the basis of voltammetry

We describe an electronic tongue which consists of a reference electrode, an auxiliary electrode and five wires of different metals (gold, iridium, palladium, platinum and rhodium) as working electrodes. The measurement principle is based on pulsed voltammetry, in which successive voltage pulses of gradually changing amplitudes are applied to the working electrodes connected in a standard three-electrode configuration. The five working electrodes were successively connected and corresponding current-response transients are recorded. The electronic tongue was used to follow the deterioration of the quality of milk due to microbial growth when milk is stored at room temperature. The data obtained were treated with principal component analysis and the deterioration process could clearly be followed in the diagrams. To make models for predictions, projections to latent structure and artificial neural networks were used. When they had been trained, both models could satisfactorily predict the course of bacterial growth in the milk samples.

The bubble electrode-a new electrode for the combination of voltammetry, electrolysis and electron spin resonance spectrometry

A new ESR-electrochemical cell with a bubble working electrode is described. To form the bubbles, the electrolyte is pumped through a mercury electrode. Electrolysis occurs in a very reproducible manner in a closed system which enables long term experiments to be carried out in the absence of light and oxygen. The cell is used in the standard three-electrode configuration so that accurate potentiostatic control is maintained during the electrogeneration of ESR sensitive species in the flow through system. Voltammograms can be recorded in the cell to enable optimization of experimental parameters for electrolysis. For short lived species, the electrode is situated immediately before or inside the cavity. In the case of moderately stable species the electrode may easily be placed outside the cavity. The advantages of this electrode are that (i) mercury is utilized as the electrode material, (ii) the electrode surface is always clean and renewed, (iii) the active electrode surface area is very large and hence the electrode is very efficient in generating redox species, (iv) the highly reproducible electrolysis conditions in the closed system make it possible to use lengthy periods of ensemble averaging to improve the signal-to-noise ratio of weak ESR signals. Data on the reduction of fluorescein and methylviologen at the bubble electrode are reported to demonstrate the use and advantages of the new ESR-electrochemical cell. The time constant of the cell has been measured and is in the range of about 1 to 10 s for flow rates up to 8 ml min −1.