Stripping analysis

However, metal traces in foods were also determined by stripping analysis. Eor example, in a recent method, the sequential voltammetric determination of Hg(II) and Cu(II) at a gold electrode, and of Cu(II), Pb(II), Cd(II), Zn(II) at an HMDE by SW anodic stripping voltammetry in matrices involved in food chain as whole meal, wheat, and maize meal, was proposed. The supporting electrolyte was 0.01 mol/1 EDTA-Na2 4- 0.06 mol/1 NaCl + 2.0 mol/1 HCIO4, and the analytical procedure was validated by the analysis of standard reference materials [25]. 

Because of its remarkable sensitivity (down to 10-11 M) stripping analysis is the most widely used voltammetric technique for trace metal determination in clinical samples (Wang, 1982A). Stripping analysis can be considered as a two-step technique. In the first step, metals in solution are effectively preconcentrated onto the working electrode by electrodeposition  

Potentiometric stripping analysis (PSA) resembles conventional stripping voltammetry in that trace metal analytes are electrolytically deposited in a thin film of mercury. However, after this preconcentration, the potentiostatic circuitry is disconnected and the amalgamated elements are chemically (rather than electrochemically) oxidized by reaction with an excess of a suitable oxidant  

Polarographic AC and pulse polarographic techniques as well as stripping analysis are effective tools for the determination of trace levels of metal ions. Table 3.1 provides a comparison of the sensitivity and usefulness of the various methods.12,21 23 For metal ions, stripping voltammetry usually is the method 

Substantial loss in sensitivity is expected for analytes with slow electron transfer kinetics. This may be advantageous for measurements of species with fast electron transfer kinetics in the presence of one (e.g., dissolved oxygen) that is irreversible. (For the same reason, the technique is very useful for the study of electron processes.) Theoretical discussions on AC voltammetry are available in the literature (17-19). 

Essentially, stripping analysis is a two-step technique. The first, or deposition step, involves the electrolytic deposition of a small portion of the metal ions in solution into the mercury electrode to preconcentrate the metals. This is followed by the stripping step (the measurement step), which involves the dissolution (stripping) of the deposit. Different versions of stripping analysis can be employed, depending on the nature of the deposition and measurement steps. 

FIGURE 3-11 Potential-time waveform used in alternating current (AC) voltammetry. 

The detection of the AC component allows one to separate the contributions of the faradaic and charging currents. The former is phase shifted 45° relative to the applied sinusoidal potential, while the background component is 90° out of phase. The charging current is thus rejected using a phase-sensitive lock-in amplifier (able to separate the in-phase and out-of-phase current components). As a result, reversible electrode reactions yield a detection limit around 5 x 10 7m. 

Shipping analysis is an extremely sensitive electrochemical technique for measuring trace metals (19,20). Its remarkable sensitivity is attributed to the combination of an effective preconcentration step with advanced measurement procedures that generate an extremely favorable signal-to-background ratio. Since the metals are preconcentrated into the electrode by factors of 100 to 1000, detection limits are lowered by 2 to 3 orders of magnitude compared to solution-phase voltammetric measurements. Hence, four to six metals can be measured simultaneously in various matrices at concentration levels down to 10 10 i. utilizing relatively inexpensive 

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Adsorptive stripping analysis involves pre-concentration of the analyte, or a derivative of it, by adsorption onto the working electrode, followed by voltanmietric iiieasurement of the surface species. Many species with surface-active properties are measurable at Hg electrodes down to nanoniolar levels and below, with detection limits comparable to those for trace metal detemiination with ASV. 

Wang J Stripping Analysis Principles, Instrumentation and Applications Ne nUe m VCH)... 

Wang J, Tian B, Wang J, Lu J, Olsen C, Yarnitzky C, Olsen K, Hammerstrom D and Bennett W 1999 Stripping analysis Into the 21st century faster, smaller, cheaper, simpler and better Tina/. Chim. Acta 385 429... 

Thioamide drugs, such as that shown here, can be determined by cathodic stripping analysis. Deposition occurs at +0.05 V... 

Wang, J. Stripping Analysis. VCH Publishers Deerfield Beach, EL, 1985, pp.116-124. 

METHOD DEVELOPMENT FOR THE POTENTIOMETRIC STRIPPING ANALYSIS OF SOLUBLE COPPER IN DENTAL MATERIALS... 

Storage of solutions for titrimetry 108 Stripping analysis see Anodic stripping voltammetry... 

Anodic shipping voltammetry (ASV) is the most widely used form of stripping analysis, hi this case, the metals are preconcenhated by elechodeposition into a small-volume mercury electrode (a tiiin mercury film or a hanging mercury drop). The preconcenhation is done by catiiodic deposition at a controlled tune and potential. The deposition potential is usually 0.3-0.5 V more negative than E° for the least easily reduced metal ion to be determined. The metal ions reach die mercury electrode by diffusion and convection, where diey are reduced and concentrated as amalgams ... 

Potentiometric stripping analysis (PSA), known also as stripping potenhometry, differs from ASV in the method used for stripping the amalgamated metals (22). hi this case, the potentiostatic control is disconnected following the preconcentration, and the concentrated metals are reoxidized by an oxidizing agent [such as O2 or Hg(II)] that is present in the solution ... 

Adsorptive stripping analysis greatly enhances the scope of stripping measurements toward numerous trace elements (23,24). This relatively new strategy involves the... 

Describe clearly the principle and operation of potentiometric stripping analysis (PSA). How it is differed from anodic stripping voltammetry (ASV) What is the quantitative signal What is its advantage over ASV ... 

While water has been used as a solvent more than any other media, nonaqueous solvents [e.g., acetonitrile, propylene carbonate, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or methanol] have also frequently been used. Mixed solvents may also be considered for certain applications. Double-distilled water is adequate for most work in aqueous media. Triple-distilled water is often required when trace (stripping) analysis is concerned. Organic solvents often require drying or purification procedures. These and other solvent-related considerations have been reviewed by Mann (3). 

Potential of zero charge, 20, 23, 25, 66 Potential scanning detector, 92 Potential step, 7, 42, 60 Potential window, 107, 108 Potentiometry, 2, 140 Potentiometric stripping analysis, 79 Potentiostat, 104, 105 Preconcentrating surfaces, 121 Preconcentration step, 121 Pretreatment, 110, 116 Pulsed amperometric detection, 92 Pulse voltammetry, 67... 

Sodium-silicate glass, 151 Sol-gel films, 120, 173 Solid electrodes, 110 Solid state devices, 160 Solvents, 102 Speciation, 84 Spectroelectrochenristry, 40 Spherical electrode, 6, 8, 9, 61 Square-wave voltammetry, 72, 92 Staircase voltammetry, 74 Standard potential, 3 Standard rate constant, 12, 18 Stripping analysis, 75, 79, 110 Supporting electrolyte, 102 Surface-active agents, 79... 

H. Chan, A. Butler, D.M. Falk and M.S. Freund, Artificial neural network processing of stripping analysis responses for identifying and quantifying heavy metals in the presence of intermetallic compound formation. Anal. Chem., 69 (1997) 2373-2378. 

Fig. 3.67. E-t curves of potentiometric stripping analysis (Psa) and its derivative (Dpsa) for 0.1 fiM Zn, Pb and Cd in 0.1 M NaCl (chemical stripping).

Experimental details on the anodic stripping analysis of metals such as Bi, Pb, Cd, Zn, Mn, Sb and Sn in Cu at the HMDE, and Ag in Cd at a glassy carbon electrode (GCE), have been given by Verbeek and co-workers122. 

Stripping analysis with inherent pre-concentration seems attractive to CFA, but until recently such a procedure appeared rather exceptional. It has been used in the automatic determination of heavy metals in water by anodic stripping voltammetry (ASV12S) in a continuous flow cell with a mercury-covered graphite electrode, having the advantage that one can distinguish... 

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