Voltammetric analyzers

The basic instrumentation required for controlled-potential experiments is relatively inexpensive and readily available commercially. The basic necessities include a cell (with a three-electrode system), a voltammetric analyzer (consisting of a potentiostatic circuitry and a voltage ramp generator), and an X-Y-t recorder (or plotter). Modem voltammetric analyzers are versatile enough to perform many modes of operation. Depending upon the specific experiment, other components may be required. For example, a faradaic cage is desired for work with ultramicroelectrodes. The system should be located in a room free from major electrical interferences, vibrations, and drastic fluctuations in temperature. 

FIGURE 4-4 Microprocessor-controlled voltammetric analyzer, in connection with an autosampler. (Courtesy of Metrohm Inc.)... 

The nature of electrochemical instruments makes them very attractive for decentralized testing. For example, compact, battery-operated voltammetric analyzers, developed for on-site measurements of metals (9,10), readily address the growing needs for field-based environmental studies. Similarly, portable (hand-held) instruments are being designed for decentralized clinical testing (11). 

A self-contained system, which integrated the remote carbon-fiber electrochemical sensor with a voltammetric analyzer and a wireless communication system, was described by Fu et al. [21]. The mobile remote underwater systems were applied for field measurements of explosive residues in marine environments. 

The carbon-fibre based voltammetric sensor has also been integrated with a diver-held unit. Such integration relied on the incorporation of the PalmSense hand-held voltammetric analyzer within a pressure vessel, with... 

An automatic system, that couples the speed of square-wave polarography with a control of the sample handling is available commercially (Yarnitzky, 1985). Further reduction in assay time is achieved using a nebulizer to eliminate the time-consuming deaeration step. Microprocessor-based voltammetric analyzers are available from companies such as EG G PAR, Metrohm, Bioanalytical Systems, ECO Chemie or Tacussel. 

In applications of voltammetry to biological samples, it is often the sample rather than the sensitive voltammetric analyzer that is the limiting factor. Getting the sample into a form that can take full advantage of the instrument capability may be the hardest part of the analysis. For this reason, the sample is usually treated prior to analysis. Such treatment releases the trace metals bound to sample components, and minimizes fouling of electrode (by adsorption of certain sample components) or background currents (from other electroactive constituents). The precision and bias of the data obtained by voltammetric analysis of biological samples will be more dependent on how well the sample is decomposed than with many other analytical techniques (e.g., atomic absorption spectroscopy which relies on atomization of the metal from the solution). 

Voltammetric measurements were performed with an AIS model DLK-100 voltammetric analyzer and a standard three electrode system consisting of a SCE reference electrode with salt bridge, a Pt counter electrode and a working electrode. In some experiments a solid state Au/Hg microelectrode was used as the working electrode and in others an EG G model 303A static dropping mercury electrode was interfaced to the analyzer. Both the Mn(III) to Mn(II) reduction and the Mn(II) to Mn(0) reduction onto the Hg electrode could be monitored simultaneously. 

For voltammetric study of the total antioxidant activity of the samples automated voltammetric analyzer Analyzer of TAA (Ltd. Polyant Tomsk, Russia) was used. As supporting electrolyte the 10 ml of phosphate buffer (pH = 6.76) with known initial concentration of molecular oxygen was used [7]. The electrochemical cell (V = 20 ml) was connected to the analyzer and consisted of a working MFE, a silver-silver chloride reference electrode with KCl saturated (Ag AgCl KCl J and a silver-silver chloride auxiliary electrode. The investigated samples (10-500 ml) were added in cell. 

The equipment requirements for ASV are simple, relatively inexpensive, and commercially available. A typical apparatus includes a three-electrode (or a two electrode, in conjunction with microelectrodes) cell, the voltammetric analyzer, and an X-Y recorder. Reliable and versatile (computerized) instruments. 

For voltammetric study of the total antioxidant activity of the samples automated voltammetric analyzer Analyzer of TAA (Ltd. Polyant Tomsk, Russia) was used. As supporting electrolyte the 10 ml of phosphate buffer (pH = 6.76) with... 

Differential voltammograms of nitrocompound-markers (supporting electrolyte - 0.01 mol/L HCl) reduction were registered by using a voltammetric analyzer IVA-5 with the scan rate of 1 V/s, scan range from 0 to -1.5 V, after 15 s holding CPE in the standard solution of nitrocompounds with intensive mixing. 

The overall design of the USB-based portable cycUc voltammetric analyzer is depicted in Figure 5.42. A miniaturized three-electrode system is connected to the built-in ADC of the PIC18F4550 microcontroUer-based data acquisition unit containing a home-made potentiostat. The overall electronic circuit diagram of the portable USB-based electrochemical analyzer is depicted in Figure 5.43. 

After getting similar results with a standard electrochemical analyzer, the portable cyclic voltammetric analyzer was further applied to detect various concentrations of cyt c. The miniaturized screen-printed electrode-based cyt c biosensor CcR-CNT-PPy-SPE as designed and characterized in Chapter 3 was used here to detect cyt c. The electrocata-lytic activity of the miniaturized CcR-CNT-PPy-SPE hiosensor toward the determination of cyt c was assessed hy the developed low-cost, home-made cychc voltammetric instrument. The accuracy of the developed instrument was also evaluated hy comparing its results with that of a commercial electrochemical analyzer imder the same experimental conditions. 

Cyclic and differential pulse voltammetric measurements were obtained from either 0.1 M TBAP/MeCl2 or 0.1 M TBAP/EtCl2 using a conventional three-electrode configuration and an IBM 225 voltammetric analyzer. A saturated calomel electrode (SCE) was used as a reference electrode in all... 

A Yanagimoto P-1000 voltammetric analyzer was used in conjunction with a Nikko Keisoku NFG-3 function generator to apply the potential to a three-electrode system, and currents were measured with a Watanabe Keisoku WX4401 X-Y recorder. 

A CV-27 potentiostat (Bioanalytical Systems) was used to conduct CV and CPC experiments an EC-225 voltammetric analyzer (IBM Instruments) was used for NPV experiments. Samples for EPR spectroscopy were sealed in the glove box, removed and frozen in liquid nitrogen as quickly as possible and stored under liquid nitrogen until spectra were run. EPR spectra were obtained at 9 K on a Varian Associates Century Series E-Line spectrometer at the University of Michigan. We thank Dr. W.R. Dunham for assistance with EPR spectroscopy. 

For d.c. polarography three instruments were used A Princeton Applied Research Model 174 Polarographic Analyzer with an MFE model 815 M Plotamatic X-Y Recorder, an IBM Mark 225 Voltammetric Analyzer with an IBM X-Y-T Recorder, and a Sargent model XVI polarograph. For the recording of differential pulse polarograms, the Princeton Applied Research model 174 with mechanical drop control (one second drop time and a pulse amplitude... 

---