Page 97 - Analytical Electrochemistry 2d Ed - Jospeh Wang

82 CONTROLLED-POTENTIAL TECHNIQUES

TABLE 3-2 Common Adsorptive Stripping Schemes for Measurement of Trace Metals
Supporting Detection
Metal Complexing Agent Electrolyte Limit, (M) Reference

Al Dihydroxyanthraquinone- BES buffer 1 10 9 25
sulfonic acid
Be Thorin Ammonia buffer 3 10 9 26
Co Nioxime Hepes buffer 6 10 12 27
Cr Diethylenetriamine-Pentaacetic Acetate buffer 4 10 10 28
acid
Fe Solochrome violet RS Acetate buffer 7 10 10 29
Mn Eriochrome Black T Pipes buffer 6 10 10 30
Mo Oxine Hydrochloric acid 1 10 10 31
Ni Dimethylglyoxime Ammonia buffer 1 10 10 32
Pt Formazone Sulfuric acid 1 10 12 33
Sn Tropolone Acetate buffer 2 10 10 34
Ti Mandelic acid Potassium chlorate 7 10 12 35
U Oxine Pipes buffer 2 10 10 36
V Catechol Pipes buffer 1 10 10 37

Depending on their redox activity, the quantitation of the adsorbed organic
compounds may proceed through oxidation or reduction. For example, modern
adsorptive stripping voltammetric and potentiometric methods represent highly
sensitive tools for detecting ultratrace levels of nucleic acids. Figure 3-17 displays
the adsorptive stripping potentiometric response of the carbon paste electrode for
0.5 ppm calf-thymus DNA following different adsorption times. Note the rapid
increase of the oxidation peak (of the guanine nucleobase) upon extending the
accumulation period. Nonelectroactive macromolecules may also be determined
following their interfacial accumulation from tensammetric peaks (resulting from
their adsorption±desorption mechanism).

3-5.4 Cathodic Stripping Voltammetry
Cathodic stripping voltammetry (CSV) is the ``mirror image'' of ASV. It involves
anodic deposition of the analyte, followed by stripping in a negative-going potential
scan:

deposition
*
A n ‡ Hg ) HgA ‡ ne 3-29†
stripping
The resulting reduction peak current provides the desired quantitative information.
Cathodic stripping voltammetry is used to measure a wide range of organic and
inorganic compounds capable of forming insoluble salts with mercury. Among these
are various thiols or penicillins, as well as halide ions, cyanide, and sul®de. Highly