ABSTRACT
Differential pulse anodic stripping voltammetry (DPASV) has been applied for characterization and quantitative detection of barium and lead from gunshot residues (GSR). Previous electrochemical techniques have detected antimony and lead from GSR, however barium has never been detected. This technique allows for simultaneous detection of Ba and Pb that is simple, fast, and nondestructive.
Subject(s)
Barium/analysis , Forensic Medicine/methods , Lead/analysis , Wounds, Gunshot , Hand , HumansABSTRACT
The diffusion coefficient values of In(III) in potassium chloride and potassium nitrate supporting electrolytes have been determined by polarography. Also, the half-wave potential, E(1/2), and the |E(3/4)-E(1/4)| values have been calculated. The results show ionic strength and chloride concentration effects on electrode kinetics in the reduction of In(III).
ABSTRACT
We review a simple recursive proportional feedback (RPF) control strategy for stabilizing unstable periodic orbits found in chaotic attractors. The method is generally applicable to high-dimensional systems and stabilizes periodic orbits even if they are completely unstable, i.e., have no stable manifolds. The goal of the control scheme is the fixed point itself rather than a stable manifold and the controlled system reaches the fixed point in d+1 steps, where d is the dimension of the state space of the Poincare map. We provide a geometrical interpretation of the control method based on an extended phase space. Controllability conditions or special symmetries that limit the possibility of using a single control parameter to control multiply unstable periodic orbits are discussed. An automated adaptive learning algorithm is described for the application of the control method to an experimental system with no previous knowledge about its dynamics. The automated control system is used to stabilize a period-one orbit in an experimental system involving electrodissolution of copper. (c) 1997 American Institute of Physics.
ABSTRACT
A new approach for background-current subtraction for flow-injection systems using potential-scanning voltammetric detection is described. The method is based on recording voltamperograms while the sample and carrier solutions flow through the cell, and taking the difference as the net response for the sample. Background currents due to hydrogen evolution, oxygen reduction, solvent oxidation or surface processes are thus compensated, and detection limits at submicromolar levels can be obtained. The compensation for oxygen reduction current means that samples do not need to be deaerated. The method has been evaluated for reproducibility, concentration dependence, detection limit, etc. A flow-cell with a stationary disk electrode, a 200-mul sample volume, and rapid differential pulse scanning are used. At a flow-rate of 0.3 ml min about 15 samples can be assayed per hour. Chlorpromazine, phenol, acetaminophen, norepinephrine, lead, cadmium, bismuth and zinc were used as test species.
ABSTRACT
The technique of reverse-pulse amperometry is applied for the detection of oxidizable organic species at a solid-electrode flow detector. Exploiting the reverse-pulse amperometric waveform gives better sensitivity than d.c. amperometric detection. Species (e.g., phenols) giving responses that are poorly separated from background are easily monitored. Reducible species can be monitored without deaeration of the solution. The effects of flow-rate, waiting time between pulses, precision, and linearity of response are reported. At a flow-rate of 1.0 ml/min injection rates of 180 samples per hour and detection limits of a few tenths of a nanogram are obtainable.
ABSTRACT
An electrochemical flow detector, based on a jet of solution directed at a thin porous carbon electrode, is described, along with its electrochemical characteristics and analytical applications. The electrode has a volume of 19 mul and surface area of 1.26 cm(2). The detector exhibits better sensitivity and detectability than a wall-jet detector. Dopamine and ferrocyanide were used as test systems to give detection limits at nanomolar concentration levels. Applications indicated include continuous-flow analysis (utilizing stopped-flow voltammetry) and flow-injection analysis.
