Concentration limits of electrolytic preconcentration in instrumental analysis

Abstract

A general mathematical model has been developed describing concentration limits for the process of electrolytic preconcentration of metal Ions by deposition. The model shows that the deposition behavior Is Initial-concentration dependent and leads to a final equilibrium concentration of metal Ions In solution, described by a single generalized equation. The model has application for practical electrolytic preconcentrations performed In connection with the following Instrumental determination.Electrolytic preconcentration is frequently used for improving limits of detection of many instrumental methods of analysis (1-3). By its application as a preliminary step, it is possible to decrease the practical limits of detection by up to 2 orders of magnitude below the usual values for the instrumental methods alone. Various instrumental methods can be coupled with the electrolytic preconcentration, and such methods, as neutron activation analysis (NAA) (4), electrothermal atomization atomic absorption spectroscopy (ETA-AAS) (5, 6), and recently inductively coupled plasma emission spectroscopy (ICP-ES) (7)(8)(9)(10)(11) proved especially valuable. These methods, coupled with the electrolytic preconcentration, achieved limits of detection in the parts-perbillion range, for several environmentally important metals in natural waters and biological fluids.Anodic stripping voltammetry (ASV) is an important method, which intrinsically combines the electrolytic precon-

Deposition of trace metals on solid electrodes: experimental verification of limits of electrochemical preconcentration

“…Two important concentration regions predicted by theoretical model (24) and confirmed by the experimental data presented in this work are those higher and lower than 10"7 M for a typical electrode surface area of 0.08 cm2. For initial concentrations higher than 10"7 M, multilayer coverage is achieved, recoveries are high, and Ceq is independent of C0 but dependent on levels of trace amounts of oxygen, anodic contaminants, and chlorine.…”

“…Values were assigned for the parameters p, s, and y. The molar monolayer area p, calculated from atomic radii by assuming closest packing of spheres on a plane accounting for 0.9069 occupation of the plane, is (3.4 and 6.4) X 10® cm2 mol"1 for copper and lead, respectively (24). The specific area of the electrodeposition cell is 8.04 X 10"3 cm"1.…”

“…A model that assumed simultaneous metal electrodeposition and chemical dissolution of deposit had proposed the establishment of different equilibrium concentrations for different ranges of initial solution concentration of metal ion being deposited (22,23). Most recently, a more general model has been developed, which leads to a single equation for the equilibrium concentration of metal ions in solution and unites two limiting approaches of the earlier model (24).…”

Anodic Stripping Voltammetry Coupled On-Line with Inductively Coupled Plasma Mass Spectrometry: Optimization of a Thin-Layer Flow Cell System for Analyte Signal Enhancement

“…However, it has been shown by theory and actual measurements that below a certain species-dependent concentration level, the rates for electrodeposition and redissolution begin to compete. 10,18,19 If this happens, a decrease in % DE will be observed. Our previous ASV-ICP-MS work with Tl showed no indication that % DE decreased with decreasing analyte concentration, at least down to a few hundred picograms per liter.…”

Multielement trace metal determination by electrodeposition, scanning electron microscopic x-ray fluorescence, and inductively coupled plasma-mass spectrometry

“…However, the difficulty of quantitative calibration has plagued this technique because the deposition is not quantitative for all elements at a given potential and the fraction deposited for a given element is not always reproducible between analyses at different concentrations (9). It has also been shown that the electrolytic preconcentration ratio frequently decreases as sample concentration decreases, due to oxidation by solution constituents (20,21). EDXRF and ICP-MS, with their multielement capability, are amenable to the use of an internal standard to solve these problems.…”