Impedance techniques chemical analysis

WILLIAM H. SMYRL is Professor of Chemical Engineering and Materials Sciences and Associate Director of the Center for Corrosion Research at the University of Minnesota. He received his Ph.D. (chemistry) at the University of California, Berkeley, and spent 3 years at the Boeing Scientific Research Laboratories and 11 years at Sandia National Laboratories. He joined the faculty of the University of Minnesota in 1984. His research interests are modeling of corrosion processes, in situ techniques for metal-metal oxide interface studies, digital impedance for faradaic analysis, stress corrosion cracking, polymer-metal interfaces, and electrochemical processes. 

Electrochemistry involves the study of the relationship between electrical signals and chemical systems that are incorporated into an electrochemical cell. It plays a very important role in many areas of chemistry, including analysis, thermodynamic studies, synthesis, kinetic measurements, energy conversion, and biological electron transport [1]. Electroanalytical techniques such as conductivity, potentiometry, voltammetry, amperometric detection, co-ulometry, measurements of impedance, and chronopotentiometry have been developed for chemical analysis [2], Nowadays, most of the electroanalytical methods are computerized, not only in their instrumental and experimental aspects, but also in the use of powerful methods for data analysis. Chemo-metrics has become a routine method for data analysis in many fields of analytical chemistry that include electroanalytical chemistry [3,4]. 

In previous publications 2 it has been shown that Low-Frequency Impedance Spectroscopy can be considered a promising, non-destructive toot for the evaluation and the analysis of incipient adhesion failure in some metal-insulator structures. The technique is based on the effect of the interface modifications on the diffusivity of chemical species such as water, which is ubiquitously present in polymers used for packaging. Since such... 

In situ cell resistance measurement, ac impedance, gas permeability, postmortem analysis using optical microscopy, SEM, TEM, NMR, IR, X-ray, neutron techniques, and chemical stmctural analysis have been used to investigate fuel cell failure mechanisms. 

The ease of incorporating funchonal groups to modify the pSi surface for mass spectrometric application has allowed for the development of a convenient and simple method for enriching the concentration of analytes. This technique, termed DIOS solid-liquid extraction (SLE), uses the property of differential adsorption selectively to capture analytes from a solution containing contaminants that impede MS analysis. Hydrophobically modified DIOS surfaces could be readily used selectively to remove interferences prior to analysis. DIOS S LE simply involves the deposition of a droplet containing analytes onto the chemically modified DIOS surface then, after approximately 3 s, the sample is aspirated with the same pipette. This short-term deposition allows for any molecule with a propensity to be adsorbed onto the surface to attach itself, while any potential hydrophilic contaminants such as salts and buffers will remain in solution, leaving the surface free from such contaminants. The van der Waals interaction between the analyte and surface leads to a selective extraction of the small molecules, while the hydrophilic contaminants such as salts are removed with the droplet. The DIOS analysis of peptides and small molecules from complex matrices is greatly enhanced by differential adsorption [47]. 

The research activities in the field of electrochemical materials science included electrochemical studies of metals and alloys, which were conducted, employing such methods as cychc voltammetry, electrochemical impedance spectroscopy, quartz crystal nanogravimetry, etc. These investigations in all cases were supported by the characterization of crystalline structure and chemical and phase composition of deposited layers, by means of transmission electron microscopy (TEM), electron diffi action, scanning electron microscopy with microprobe (EDX) analysis. X-ray and Auger electron spectroscopies (XPS), and X-ray diffraction (XRD) techniques. The latter studies were conducted in collaboration with the colleagues from the ICh department of materials strucmre characterization (R. Juskenas, A. Selskis, and V. Jasulaitiene). 

The ionic polarisation cell technique involves transport under a chemical potential and electrical gradient and, therefore, includes the contributions of both charged and neutral species. The AC procedure has been suggested by Sorensen and Jacobsen (1982) and is based on the theory of MacDonald (1973,1974) which involves analysis of the impedance spectra of the symmetric cell MIP MXIM. 

---