Adsorptive stripping voltammetry AdSV

The four variations of this technique are to be found in Table 14.2. The schemes of operation are shown in Fig. 14.6. Important applications for trace metals are the use of anodic stripping voltammetry (ASV) to determine trace quantities of copper, cadmium, lead and zinc, and adsorptive stripping voltammetry (AdSV) of trace quantities of nickel and cobalt—pre-concentration by adsorption accumulation of the oxime complexes followed by reduction to the metal is employed, as reoxidation of these metals in ASV is kinetically slow and does not lead to well-defined stripping peaks. 

Adsorptive stripping voltammetry (AdSV) is of increasing importance in trace determinations of pharmaceutical compounds. In this method, the preconcentration step is adsorptive rather than electrolytic, resulting in an adsorbed film of the analate on the electrode surface. The stripping step typically uses LSV or the differential pulse mode in either the cathodic or anodic direction, as required. The HMDE is typically used for cathodic reductive stripping, whereas carbon or noble metal electrodes are used in the adsorptive mode. 

Fig. 14.27 Automated adsorptive stripping voltammetry (AdSV) of Ni2+ ions (a) calibration plot derived from the peak current of DPVs of automated AdSV using the standard addition method (b) Long-term Ni2+ ions release from surfaces of electropolished NiTi shape memory alloys kept in NaCl solution. NaCl concentrations were either 15wt.% solid line) or 0.9wt.% dotted line).78 (Reproduced by permission of Wiley-VCH Verlag GmbH Co KGaA)...

Ni concentrations measured in air, grass and water by adsorptive stripping voltammetry (AdSV), by AAS and X-ray fluorescence (XRF) are compared in Table 10. ... 

We have recently demonstrated similar findings for several antigen-antibody reactions at the hanging mercury drop electrode (HMDE) using the technique of adsorptive stripping voltammetry (AdSV). These have included the reaction of human serum albumin (HSA) with anti-HSA, mouse IgG with anti-mouse IgG and hCG with two anti-/ -hCG antibodies. In all cases, the current observed following accumulation of the antigen (at the HMDE) decreased on addition of the specific antibody. This is illustrated for the case of mouse IgG with anti-mouse IgG in Fig.l. 

Improved sensor respraise to several organic species can be achieved by exploiting the high adsorption capability of carbon surfaces, in adsorptive stripping voltammetry (AdSV). This procedure, based on very similar principles of solid phase microextraction (SPME), implies that analytes are pre-concentrated at carbon nanostructured surfaces prior to voltammetric detection. It has been successfully... 

In adsorptive stripping voltammetry (AdSV) metal chelates and organic molecules are accumulated by adsorption at the surface of the working electrode. If these compounds are electrochemically active, i.e., if they are reducible or oxidizable. their subsequent voltammetric determination is possible. By this principle of so-called adsorptive stripping voltammetry, organic and organomet-allic compounds are determined in the ultra-trace range. This technique is particularly important for the trace analysis of metals that are not readily deposited as the element on mercury electrodes... 

An indirect adsorptive stripping voltammetry (AdSV) method on a mercury drop working electrode has been used for determination of cyanide ions and HCN [51]. The method is based on competitive Cu complex formation reaction between adenine at the electrode surface and CN ions in solution. In this method, cyanide changed the cathodic adsorptive stripping peak height of Cu-adenine. A linear decrease of the peak current of Cu-adenine was observed when the cyanide concentration was increased. 

Adsorptive stripping voltammetry (AdSV) is based on the accumulated adsorption of a complex between the analyte and a complexing agent at the electtode surface, often at an applied potential chosen so as to help the adsorption process. Either the metal ion or the ligand can be measured in the presence of an excess of the other component in bulk solution. Usually, the determination step involves reduction of the metal ion from the adsorbed complex. Adsorption follows an isotherm, usually of Langmuir type [3]. 

Explain the technique of adsorptive stripping voltammetry (AdSV). Carbon electrodes are often modified with a layer of carbon nanotubes to increase the sensitivity of AdSV. Suggest a reason why, and discuss the types of analytical targets that might most usefully benefit from this approach. 

Generally, the hanging mercury drop electrode (HMDE) is the most suitable electrode for anodic stripping voltammetry (ASV) and adsorptive stripping voltammetry (AdSV) analyses because such electrode allows fast and reproducible surface renewal and provides high adsorptivity for organic compounds. Nevertheless, even HMDE has some drawbacks that limited its use particularly for automatic or on-site voltammetry analysis as well as analysis in flow conditions since it requires a mercury reservoir and regular maintenance of the capillary and... 

The strong adsorption of organic molecules occurring at carbon surfaces can be exploited to improve the sensitivity of the sensor response toward several organic species analytes can be pre-concentrated at carbon nanostructured surfaces in advance to the actual voltammetric detection, following an approach very similar to Solid Phase MicroExtraction (SPME). This analytical procedure, called Adsorptive Stripping Voltammetry (AdSV) has been applied for the detection of electroactive species of interest in the environmental field, such as herbicides or nitro-derivatives. Thanks to the occurrence of mechanisms similar to those... 

Thus, classical electrochemical stripping analysis (ESA) had spawned an offspring—adsorptive stripping voltammetry (AdSV) that became soon one of the most frequent techniques in electrochemical trace determination of metals (see, e.g., reference (113) and references therein). The determinations by AdSV and the related potentiometric method, constant current (adsorptive) stripping analysis, CCSA, are characterised by high selectivity which can be yet improved in the open-circuit arrangement and/or medium exchange.AdSV also offers remarkable detection capabilities down to the nanomolar level (see Table 5.2 and references (94, 97, 108, 110)). 

The study of the inhibition of parahydroquinone oxidation at a graphite electrode in the presence of a surfactant (phospholipid) was reported by Schmidt and Emons. The decrease of the parahydroquinone oxidation peak was related to the surfactant concentration. In a similar approach, using ferrocene in a CPE as a redox tracer, Kim et determined different surfactants via modification of the ferrocene redox behavior. In the presence of DS, the oxidation peak current of ferrocene was enhanced by a factor of 3.5. A limitation of the technique was the analysis time because the electrode-solution contact period was 1 h. Similarly, anionic polyelectrolytes were determined by adsorptive stripping voltammetry (ADSV) at a carbon paste electrode in the presence of 11-ferrocenyltrimethyltmdecyl ammonium ions. The ion-association complex between an anionic polyelectrolyte and the ferrocenyl cationic surfactant was adsorptively accumulated at the electrode in the absence of an apphed potential. The concentration of the anionic sxufactant was indirectly evaluated from the oxidation wave of the ferrocenyl cationic sxufactant. By means of AdSV, levels of anionic siufactants of 10 mol could be measured with good selectivity. 

---