Thiocyanate-selective membranes using

As described above, significant progress in the design of anion and gas selective membrane electrodes has been made. While further work is needed to understand fully the response mechanisms and to improve the performance of the new thiocyanate, salicylate, and sulfite selective membrane electrodes, each of these sensors appears to offer adequate selectivity for use in real sample measurements. In addition, by carefully... 

Several authors have also reported the potential use of electropolyme-rized metalloporphyrin films as new electrode materials for anion detection and pH measurements. For example, Daunert et al reported that anion-selective membrane electrodes can be prepared by electropolymerizing aniline-substituted cobalt tetraphenylporphyrin complexes onto a glassy carbon surface. It was shown that the resulting electrodes are highly selective towards the detection of thiocyanate and nitrite anions. The mechanism by which these metalloporphyrin electrode sensors operate is probably related to the well-known axial complexation capability of the central metal cation of the porphyrin towards different kind of anions and bases. The same authors also reported a detection limit of 5 x 10 M for these ion-selective electrodes which have lifetimes of more than 2 months... 

The thiocyanate ion-selective electrode [21,247] This has a heterogeneous membrane containing AgCNS. It is used for the determination of the activity of SCN in suspensions of submitochondrial particles and chromatophores from Rhodospirillum rubrum in order to measure the membrane potential of these particles [200], as well as for other applications. 

A hydrophobic cobyrinate (Figure 2, structure 2) was used to prepare solvent polymeric membranes (10). The typical membrane composition was 1% (w/w) ionophore, 66% (w/w) plasticizer and 33% (w/w) polymer. Electrodes prepared with this ionophore, dioctyl sebacate (DOS) and poly(vinyl chloride) (PVC) presented, at pH 6.6, the selectivity pattern shown in Figure 3. The response of the electrodes was near-Nernstian for salicylate, thiocyanate, and nitrite. Their selectivity behavior clearly deviates from that of the Hofmeister series, with nitrite being the anion that presents the larger deviation. 

The current response of a GCE used for AMD was greatly improved after modification with polyhistidine. LOD was 6 nM for dopamine (10a), 8 nM for epinephrine (15a) and 20 nM for catechol (42). The modified electrode has also been applied for AMD after CE37. PVC membranes were designed to serve as selective barriers for the amperometric detection of phenols and elimination of thiocyanate interference . 

Selectivity of the Hg(DDC)2-based membrane toward sulfite relative to other anions correlates with what one might expect for anionic species interacting with the Hg(II) center of the complex. As shown in Table III, iodide, bromide, thiosulfate, and thiocyanate are major interferents. However, the membrane exhibits little or no response to a wide range of other anions including sulfate, phosphate, chloride, and nitrate, making it potentially useful as an analytical sensor for measurements in certain samples, e.g., in monitoring added sulfite levels in food and beverages. 

Several investigators have developed PVC-based electrodes by using lipophilic Co(nptetraphenylporphyrins as ionophores 20,22,23). These electrodes were also selective for thiocyanate but had short lifetimes, as demonstrated by the fact that their slopes deteriorated in just a few weeks (22,25). The shorter lifetime of PVC-based ISEs has been attribute to leaching of Ae ionophore from the sensor matrix (5-6). Hodinar and Jyo have also proposed that decreased slopes may be due to crystallization of the ionophore in the membrane (22). Both the PVC electrodes and the electropolymerized films that utilize cobalt porphyrins as ionophores respond primarily to thiocyanate, but their selectivity properties are quite ctifferent In fact,... 

---