Stripping voltammetry of copper and lead using gold electrodes modified with self-assembled monolayers

One problem associated with using bare solid metal electrodes, such as gold and platinum, in stripping analysis to determine heavy metal ions such as lead and copper ions in dilute solutions is that underpotential deposition (UPD) gives multiple stripping peaks in the analysis of mixtures. These peaks are often overlapped and cannot be conveniently used for analytical purposes. Bifunctional alkylthiols, such as 3-mercaptopropionic acid, with an ionizable group on the other terminal end of the thiol can form self-assembled monolayers (SAMs) on the surface of the gold electrode. It is shown that such an SAM-modified gold electrode minimizes the UPD effects for the stripping analysis of lead and copper. The anodic peak potential shifts and the peak shape changes, indicating that the SAM changes the deposition and stripping steps of these heavy metal ions. Thus, the sensitivity levels for both single species and mixtures can be significantly improved for the conventional solid electrodes. The mechanism of the deposition reaction at the SAM-modified gold electrodes is discussed. Received: 29 May 1997 / Accepted: 24 June 1997     

Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device. 19. Preparation and Characterization of Films of Quaternized Poly(4‐vinylpyridine)‐silica

Quaternized poly(4‐vinylpyridine) (QPVP) has been incorporated as an anion exchanger into sol‐gel derived silica films for use in a spectroelectrochemical sensor. The preparation, characteristics and performance of these films are described. The films, which are spin‐coated onto the surface of a planar optically transparent electrode, are optically transparent and uniform. Scanning electron microscopy and spectroscopic ellipsometry have been used to examine film structure, thickness and optical properties. These films have been shown both spectroscopically and electrochemically to preconcentrate ferrocyanide, a model analyte for the sensor. The films can be regenerated for multiple measurements by exposure to 1 M KNO₃. The effects of polymer molecular weight and storage conditions on film performance are described. The overall response of this film is comparable to the poly(dimethyldiallylammonium chloride)‐silica films previously used for this sensor.     

The spectroscopy of salicylaldehydes: Electronic absorption spectra

Measurements of the electronic absorption spectra of vapor- and solution-phase salicylaldehydes are reported for wavelengths ≥1900 Å. Three intense absorption band systems are readily assigned as $\text{A′ (ππ}{}^1\text{) ← 1}{}^1\text{A′}$ transitions by comparison with all-valence-electron computations. Moderate vibrational structure in the $\text{3}{}^1\text{A′ (ππ}{}^1\text{) ← 1}{}^1\text{A′}$ transitions of isotopic salicylaldehydes is analyzed and tentative assignments are made for the coupled vibrations.     

The 2644-Å band system of fluorobenzene. The hot-band spectrum

The 2644-Å band system of fluorobenzene and two deuterated isotopes has been photographed and a vibrational analysis proposed. The present paper is limited to the hot-band spectrum. Several in-plane fundamental vibrations in the ground electronic state can be identified, and these agree quite well with values obtained from infrared spectroscopy. The major sequence bands have also been identified. Anharmonic coupling between vibrations 11 and 16a plays a major role in these isotopes, and this is described in detail.     

An online fiber-optic UV-visible detector for continuous free-flow electrophoresis

A PC-controlled, scanning online UV detector for continuous free-flow electrophoresis (CFFE) was designed to allow for single UV wavelength monitoring across a 1-D array of 48 longitudinal flow cells interfaced to a CFFE apparatus. In the detection scheme, the UV light is sequentially passed through each of the flow cells. The design integrates online acquisition of absorbance spectra of components separated by CFFE. Benzoic acid standard solutions were used to examine the performance of the detector. Chloroquine diphosphate and 4-nitrophenol were used as test solutes to determine the detector's ability to distinguish analytes separated in the CFFE.     

Development and Application of Novel Thin-Film Spectroelectrochemical Sensors Possessing Three Modes of Selectivity*

A thin-film spectroelectrochemical sensor design employing three modes of selectivity is described. Selectivity is achieved through (1) partitioning of the analyte into a chemically selective film, (2) electrochemical cycling of the analyte over a given potential window, and (3) absorbance of one of the redox states of the analyte at the chosen analytical wavelength. Optimization of the sensor is described with respect to both improved selectivity and sensitivity, as well as its response to a number of different chemical species. Lastly, application of the sensor for determination of ferrocyanide, Fe(CN)^4- ₆, in both radioactive waste simulant and actual waste storage tank contents is given.