James Q. Chambers

Amperometric determination of glucose with a ferrocene-mediated glucose oxidase/polyacrylamide gel electrode

Abstract Enzyme electrodes were constructed by immobilization of glucose oxidase and ferrocene into cross-linked polyacrylamide gels. Electrogenerated ferrocinium ion acts as a direct electron mediator between glucose oxidase and a reticulated vitreous carbon (RVC)/graphite support bed. The electrode is easily constructed, gives a current response proportional to glucose concentrations up to 30 mM, and has good chemical stability in water and air.

Individual and simultaneous determination of lead, cadmium, and zinc by anodic stripping voltammetry at a bismuth bulk electrode.

A bismuth bulk electrode (BiBE) has been investigated as an alternative electrode for the anodic stripping voltammetric (ASV) analysis of Pb(II), Cd(II), and Zn(II). The BiBE, which is fabricated in-house, shows results comparable to those of similar analyses at other Bi-based electrodes. Metal accumulation is achieved by holding the electrode potential at -1.4V (vs. Ag/AgCl) for 180 s followed by a square wave voltammetric stripping scan from -1.4 to -0.35 V. Calibration plots are obtained for all three metals, individually and simultaneously, in the 10-100 microg L(-1) range, with a detection limit of 93, 54, and 396 ng L(-1) for Pb(II), Cd(II), Zn(II), respectively. A slight reduction in slope is observed for Cd(II) and Pb(II) when the three metals are calibrated simultaneously vs. individually. Comparing the sensitivities of the metals when calibrated individually vs. in a mixture reveals that Zn(II) is not affected by stripping in a mixture. However, Pb(II) and Cd(II) have decreasing sensitivities in a mixture. The optimized method has been successfully used to test contaminated river water by standard addition. The results demonstrate the ability of the BiBE as an alternative electrode material in heavy metal analysis.

Column efficiency and radial homogeneity in liquid chromatography

Local, on-column electrochemical detection was carried out in the amperometric mode at different points of the column outlet cross-section. This permitted the determination of the spatial distribution of analyte molecules within the chromatographic zone at the column exit. The radial distribution of the peak-maximum velocity, the local efficiency and the analyte concentration were determined for a commercial column and for several laboratory-packed columns made with different solid particles and with a commercial silica-based stationary phase. An important region of the packing close to the wall is denser, has a lower permeability and a lower efficiency than the core of the packing. The concentration along the wall is lower than average, in part because of the lower efficiency.

Electrochemical Reduction of Nitrate and Nitrite in Concentrated Sodium Hydroxide at Platinum and Nickel Electrodes

This work describes the electrochemical reduction of nitrate in alkaline solutions. Conditions which maximize the current efficiency for the production of dinitrogen and/or ammonia gases could be very important for the treatment of radioactive waste solutions.

Monitoring microbiol adhesion and biofilm formation by attenuated total reflection/Fourier transform infrared spectroscopy

Abstract A major problem in accurately defining bacterial adhesion mechanisms and processes occurring in biofilms on surfaces is the lack of techniques that nondestructively provide on-line information about the microorganisms, their extracellular polymers, and metabolites. The attenuated total reflectance (ATR) technique of Fourier transform infrared spectroscopy (FT-IR) is ideally suited to monitor molecular interactions at the solution/internal reflection element (IRE) interface, and we report its application to biofilm research. Two methodologies were utilized to obtain the ATF/FT-IR spectra of living Caulobacter crescentus cells attached to germanium crystals. Initially, spectra of attached bacteria in high purity water produced molecular details of the attachment process without spectral interferences from components of the medium. A growth medium, utilized in the second method, allowed direct examination of the infrared absorption bands associated with the actively growing microorganisms on the surface of the IRE in the spectral region of 2000 to 1200 cm −1 . Using the amide II band as a marker for biofilm biomass, the detection limit was determined to be approximately 5 × 10 5 cells·cm −2 . These results proved that the ATR-FT/IR methodologies can be utilized to provide chemical information from bacteria and bacterial products located within approximately 1 μm of the surface without spectral interferences due to components of the medium.

Flower-like self-assembly of gold nanoparticles for highly sensitive electrochemical detection of chromium(VI).

We report here the fabrication of a flower-like self-assembly of gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) as a highly sensitive platform for ultratrace Cr(VI) detection. Two AuNP layers are used in the current approach, in which the first is electroplated on the GCE surface as anchors for binding to an overcoated thiol sol-gel film derived from 3-mercaptopropyltrimethoxysilane (MPTS). The second AuNP layer is then self-assembled on the surface of the sol-gel film, forming flower-like gold nanoelectrodes enlarging the electrode surface. When functionalized by a thiol pyridinium, the fabricated electrode displays a well-defined peak for selective Cr(VI) reduction with an unusually large, linear concentration range of 10-1200 ng L(-1) and a low detection limit of 2.9 ng L(-1). In comparison to previous approaches using MPTS and AuNPs on Au electrodes, the current work expands the use of AuNPs to the GCE. Subsequent functionalization of the secondary AuNPs by a thiol pyridinium and adsorption/preconcentration of Cr(VI) lead to the unusually large detection range and high sensitivity. The stepwise preparation of the electrode has been characterized by electrochemical impedance spectroscopy (EIS), scanning electronic microscopy (SEM), and IR. The newly designed electrode exhibits good stability, and has been successfully employed to measure chromium in a pre-treated blood sample. The method demonstrates acceptable fabrication reproducibility and accuracy.

Spectroelectrochemistry of tetracyanoquinodimethane modified electrodes

Abstract Thin films of a tetracyanoquinodimethane (TCNQ) oligomer adsorbed on optically transparent platinum electrodes have been studied using spectroelectrochemical techniques. In contact with aqueous electrolytes the electron aceptor sites in these modified electrodes are reduced to mixtures of the radical aion, TCNQ ⨪ , the dimer radical anion, TCNQ 2− 2 , the dimer dianion, TCNQ 2 2− , and the dianion, TCNQ 2∮ . Electrolyte effects on the reduction process and the stability of the reduced films were studied. Both monovalent and divalent ions exhibited Nernstian potential dependence, and in the presence of Ca 2+ ions the dianion state was stabilized. Counterion effects are suggested as the origin of variations in the wave shape in multcycle voltammograms.

Radiotracer study of the sorption of counter- and co-ions in tetracyanoquinodimethane and poly(vinyl ferrocene) modified electrodes

Abstract Sorption of Ca2+ and SO2−4 ions into TCNQ and PVF surface films has been studied under potentiostatic steady state conditions and during potential cycling using a radiotracer technique. It has been shown that the sorption of the counter- and co-ions follows the charge and discharge processes occurring in the film. No sorption of ions has been found in the case of virgin films. No equilibrium in regard with the electrolyte is attained during potential cycling even at slow sweep rates. In the case of TCNQ electrodes the equilibrium concentration of counter-ions in the film is associated with the equilibrium concentration of different dimerized species.

Multichannel ATR/FT-IR spectrometer for on-line examination of microbial biofilms

Microorganisms in aqueous environments attach to exposed surfaces, proliferate, excrete extracellular polymers, and form gelatinous layers termed biofilms. By altering interfacial chemistry, biofilms produce both beneficial and detrimental effects in natural environments, industry, and medicine. For example, biofilms cause infections in patients as well as the failure of many implanted medical devices, result in dental carries, and create conditions favorable for corrosion of metal structures in industry. In addition, biofilms are the source of free-floating microorganisms in high-purity water systems and can cause problems in the manufacture of semiconductor devices. Biofilms beneficially degrade waste in water treatment plants and ground water pollutants such as trichloroethylene. Thus, instrumentation providing information about the function, physiology, and effects of biofilms is required to increase our understanding of these complex interactions between the biofilm and its environment.

Electrocatalytic reduction of nitrate and nitrite at nafion R-coated electrodes in concentrated sodium hydroxide solution

The electrochemical reduction of nitrate ions in alkaline solution has been studied using various cathode materials and is the basis for a patent describing the conversion of nitrate into hydroxide ion in carbonate solutions. Recently, Taniguchi et al. have reported that certain well studied transition metal cyclic amine complexes, namely Co(III)-cyclam and Ni(II)-cyclam where cyclam is 1,4,8,11-tetraazacyclotetradecane, efficiently electrocatalyze the reduction of nitrate and nitrite to hydroxylamine at mercury electrodes. Here the authors report that the metal cyclam catalyst can be incorporated into a Nafion film electrode, and that the reduction of nitrate and nitrite proceeds efficiently at these electrodes in concentrated NaOH solution. Nafion is a perfluoroalkanesulfonated cation exchange material that has been widely used to immobilize redox couples at electrode surfaces, including electrocatalysis species.