Thallium electrode

Casella IG, Gatta M (2004) Electrochemical reduction of N03 - and NO 2 - on a composite copper thallium electrode in alkaline solutions. J Electroanal Chem 568 183-188... 

Thallium electrode is a second-kind electrode composed of thallium amalgam (40 %) and a thallium salt, most often thaUium(I) chloride, but also thallium(l) bromide or sulfate can be used [148, 149] ... 

Reference Electrodes and Liquid Junctions. The electrical cincuit of the pH ceU is completed through a salt bridge that usually consists of a concentrated solution of potassium chloride [7447-40-7]. The solution makes contact at one end with the test solution and at the other with a reference electrode of constant potential. The Hquid junction is formed at the area of contact between the salt bridge and the test solution. The mercury—mercurous chloride electrode, the calomel electrode, provides a highly reproducible potential in the potassium chloride bridge solution and is the most widely used reference electrode. However, mercurous chloride is converted readily into mercuric ion and mercury when in contact with concentrated potassium chloride solutions above 80°C. This disproportionation reaction causes an unstable potential with calomel electrodes. Therefore, the silver—silver chloride electrode and the thallium amalgam—thallous chloride electrode often are preferred for measurements above 80°C. However, because silver chloride is relatively soluble in concentrated solutions of potassium chloride, the solution in the electrode chamber must be saturated with silver chloride. 

Stripping voltammetry procedure has been developed for determination of thallium(I) traces in aqueous medium on a mercury film electrode with application of thallium preconcentration by coprecipitation with manganese (IV) hydroxide. More than 90% of thallium present in water sample is uptaken by a deposit depending on conditions of prepai ation of precipitant. Direct determination of thallium was carried out by stripping voltammetry in AC mode with anodic polarization of potential in 0,06 M ascorbic acid in presence of 5T0 M of mercury(II) on PU-1 polarograph. 

Due to the experimental difficulties involved, there have been only three reports of XSW measurements at electrochemical interfaces. Materlik and co-workers have studied the underpotential deposition of thallium on single-crystal copper electrodes under both ex situU9 and in situ120 conditions. In addition, they report results from studies in the absence and presence of small amounts of oxygen. 

In the ex situ studies, the thallium layer was electrodeposited and the electrode was subsequently removed from solution and placed inside a helium-filled box where the XSW experiments were carried out. 

Just a few years after the discovery of the deposition and electroactivity of Prussian blue, other metal hexacyanoferrates were deposited on various electrode surfaces. However, except for ruthenium and osmium, the electroplating of the metal or its anodizing was required for the deposition of nickel [14], copper [15,16], and silver [9] hexacyanoferrates. Later studies have shown the possibilities of the synthesis of nickel, cobalt, indium hexacyanoferrates similar to the deposition of Prussian blue [17-19], as well as palladium [20-22], zinc [23, 24], lanthanum [25-27], vanadium [28], silver [29], and thallium [30] hexacyanoferrates. 

A.K. Jain, R.P. Singh, and C. Bala, Solid membranes of copper hexacyanoferrate(III) as thallium(I)-sensitive electrode. Anal. Lett. 15, 1557-1563 (1982). 

S.M. Chen, K.T. Peng, and K.C. Lin, Preparation of thallium hexacyanoferrate film and mixed-film modified electrodes with cobalt(II) hexacyanoferrate. Electroanalysis 17, 319 (2005). 

H. Kahlert, S. Komorsky-Lovric, M. Hermes, and F. Scholz, Prussian blue-based reactive electrode (reactrode) for the determination of thallium ions. Fresenius J. Anal. Chem. 356, 204-208 (1996). 

J.M. Zen, H. Ho, and P.Y. Chen, Voltammetric determination of thallium on a Prussian blue/cinder paste electrode. Indian J. Chem. Sect. A Inorgan. Bio-Inorgan. Phys. Theoret. Anal. Chem. 42, 839—842 (2003). 

Haapakka and Kankare have studied this phenomenon and used it to determine various analytes that are active at the electrode surface [44-46], Some metal ions have been shown to catalyze ECL at oxide-covered aluminum electrodes during the reduction of hydrogen peroxide in particular. These include mercu-ry(I), mercury(II), copper(II), silver , and thallium , the latter determined to a detection limit of <10 10 M. The emission is enhanced by organic compounds that are themselves fluorescent or that form fluorescent chelates with the aluminum ion. Both salicylic acid and micelle solubilized polyaromatic hydrocarbons have been determined in this way to a limit of detection in the order of 10 8M. 

We will use the example of thallium ion. The potential of the working electrode will be stepped from a potential at which only Tl" " is the stable form to a potential at which only is the stable form. Figure 6.2(a) shows a plot of potential against time - note that the rise in potential here is essentially vertical. It would be completely vertical but for the requirement to charge the doublelayer around the electrode. The potential before the step is, e.g. 0 V, i.e. it is well cathodic (negative) of, .,+(= 1.252 V), so Tl is the only stable redox form, and no Tl " " will form. Thie potential after the step is, e.g. 1.6 V, i.e. it is well anodic of 3+. p,+, so Tl is the only stable redox form here, thus causing Tl" to oxidize to Tl +. 

The value of[Tl ] in the solution bulk remains essentially constant since only a tiny proportion of the overall amount of Tl is oxidized, but at the surface of the electrode we can say, to a good approximation, that [Tt ] = 0. Very soon after the potential is stepped, Tl from the bulk diffuses toward the electrode, thereby attempting to even out the concentration gradient, i.e. to replenish the Tt" that was consumed at the commencement of the step. W need to recognize, however, that these thallium ions will not remain as Tl for long as they will be oxidized immediately to form Tl, i.e. as soon as they impinge on the electrode. The end result is that a concentration gradient will soon form after the potential has been stepped. 

Elemental composition T191.49%, F 8.51%. An appropriately diluted aqueous solution may be analyzed for thaUium by AA or ICP methods (See Thallium) and for the F ion by the fluoride ion-specific electrode or by ion chromatography. 

Dropping indium and thallium amalgam electrodes [41] were used to determine kinetic parameters of Zn(II) reduction as a function of the amalgam composition. The formal potentials were shifted to more negative values with increasing thallium and indium amalgam concentrations. 

Finally, Adzic and Wang [62], and Wang etal. [63] have studied the formation of thallium bromide on Au(lll) electrode... 

The bromide-induced adsorption of thallium complex on pc-Ag electrode has been studied using CV and chronocoulome-try [125]. 

Waszczuk et al. [329] have carried out radiometric studies of UPD of thallium on single-crystal Ag electrode from perchloric acid solutions. Deposition of Tl on Ag(lOO) to obtain monolayer, bilayer, and bulk crystallites has been studied by Wang et al. [330]. These studies have shown that apart from the substrate geometry, the nature of the substrate-adatom interactions also influence the structure of the UPD metal adlayers. This is because of the fact that, contrary to Au and Pt electrodes, Tl forms a well-ordered bilayer phase before bulk deposition on Ag(lOO) surface occurs. 

Propylene Carbonate (PC) and Water. Data from both spectroscopic and thermodynamic studies for other solvent systems are sparse and some of it is of doubtful quality. For propylene carbonate, Salomon (40) has obtained emf data using lithium metal and thallium amalgam-thallous chloride or bromide electrodes. 

The electrosorption valency usually increases as the underpotential decreases to approach the ionic charge (total discharge of the cation) close to the Nernst potential, for instance in the case of lead and thallium upd on silver [114]. However, the co-adsorption of anions may contribute to the observed apparent electrosorption valence, as rotating ring disc electrode (RDE) experiments have shown [113]. 

Fig. 1. Simultaneous separation and detection of anions and cations on a latex agglomerate column. Column Dionex HPIC-CS5 cation exchange column (250X2 mm) with precolumn HPIC-CG5 (50 X 4 mm) eluent 0.5 mM copper sulfate, pH 5. 62 flow rate 0.5 ml/min sample volume 20 gl containing 0.1 m M of each ion detection two potentiomet-ric detectors equipped with different ion-selective electrodes in series. Peaks (1) chloroacetate, (2) chloride, (3) nitrite, (4) benzoate, (5) cyanate, (6) bromide, (7) nitrate, (8) sodium, (9) ammonium, (10) potassium, (11) rubidium, (12) cesium, (13) thallium. Reprinted with permission from [10].

In one approach crown ethers (31) or (32) are mixed with PVC and a plasticizer such as o-ni-trophenyl octyl ether in THF to give a membrane on evaporation of the solvent. Discs may then be cut and incorporated into electrodes. The resulting electrodes show good selectivity for thallium(I) and are useful in the measurement of thallium concentrations.88... 

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