Metal cation electrochemical sensors

In this example, the mptt-modified surface previously described [11] will be used. Such a sihca-modified surface can successfully used to promote the electrochemical determination (by redissolution voltammetry) of Co and Ni in aqueous solutions. It is found that both species can be simultaneously investigated in the concentration range 10 —lO moldm .  

The detailed preparations and experimental conditions will be not reported here, but the electrochemical determinations were performed by using a modified carbon paste (CP) electrode produced by using the modified sifica surface as sensitive species. The main experimental conditions and results are summarized in Figs. 3.11 and 3.12 and Table 3.2. 

Based on the obtained experimental results, it is possible to verify that the mptt-modified surface can be successfully used to produce modified CP electrodes 

Chemistry on Modified Oxide and Phosphate Surfaces Fundamentals and Applications 

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The electrochemical properties of ferrocene have been utilized by many workers in the field of electrochemical molecular recognition. Saji (1986) showed that the previously synthesized (Biernat and Wilczewski, 1980) ferrocene crown ether molecule (Fig. 3 [1]), whose binding properties had previously been studied only by nmr and UV/Vis techniques (Akabori et al., 1983), could be used as an electrochemical sensor for alkali metal cations involving a combination of through-space and through-bond interactions. 

The scope of the tether-directed remote functionalization has been expanded from Cgo to the higher fullerene C70, and the described reactions are completely regioselective, featuring, in the case of C70, the kinetically disfavored addition pattern. The crown ether is a real template, since it can be readily removed by transesterification, giving a much-improved access to certain bis-adducts that are not accessible by the direct route. Cation-binding studies by CV reveal that cyclophane-type crown ethers derived from C60 and C70 form stable complexes with metal cations, and a perturbation of the fullerene reduction potentials occurs because the cation is tightly held close to the fullerene surface. This conclusion is of great importance for future developments of fullerene-based electrochemical ion sensors. 

Supramolecules containing metal-polypyridine units, especially the Ru(dpp)-based dendrimers, could be used as electron reservoirs or components of molecular-electronic devices. Supramolecules in which an electroactive M(N,N) group is attached to a receptor capable of molecular recognition (crown ethers, calixarenes, cryptands etc.) can work as electrochemical sensors. Electrochemical recognition of cations as well as anions has been reported [33-35, 257, 263]. 

Due to their ability to coordinate metal cations, as well as interact with organic species, the amorphous oxide-modified surfaces can be successfully used to produce electrochemical sensors [10], as will be illustrated by two specific examples. 

Multiple electrodes have been used to obtain selectivity in electrochemical detection. An early example involved the separation of catecholamines from human plasma using a Vydac (The Separation Group Hesperia, CA) SCX cation exchange column eluted with phosphate-EDTA.61 A sensor array using metal oxide-modified surfaces was used with flow injection to analyze multicomponent mixtures of amino acids and sugars.62 An example of the selectivity provided by a multi-electrode system is shown in Figure 2.63... 

The participation of cations in redox reactions of metal hexacyanoferrates provides a unique opportunity for the development of chemical sensors for non-electroactive ions. The development of sensors for thallium (Tl+) [15], cesium (Cs+) [34], and potassium (K+) [35, 36] pioneered analytical applications of metal hexacyanoferrates (Table 13.1). Later, a number of cationic analytes were enlarged, including ammonium (NH4+) [37], rubidium (Rb+) [38], and even other mono- and divalent cations [39], In most cases the electrochemical techniques used were potentiometry and amperometry either under constant potential or in cyclic voltammetric regime. More recently, sensors for silver [29] and arsenite [40] on the basis of transition metal hexacyanoferrates were proposed. An apparent list of sensors for non-electroactive ions is presented in Table 13.1. 

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