Sulfides, silver electrodes

Surface heterogeneity may be inferred from emission studies such as those studies by de Schrijver and co-workers on P and on R adsorbed on clay minerals [197,198]. In the case of adsorbed pyrene and its derivatives, there is considerable evidence for surface mobility (on clays, metal oxides, sulfides), as from the work of Thomas [199], de Mayo and co-workers [200], Singer [201] and Stahlberg et al. [202]. There has also been evidence for ground-state bimolecular association of adsorbed pyrene [66,203]. The sensitivity of pyrene to the polarity of its environment allows its use as a probe of surface polarity [204,205]. Pyrene or ofter emitters may be used as probes to study the structure of an adsorbate film, as in the case of Triton X-100 on silica [206], sodium dodecyl sulfate at the alumina surface [207] and hexadecyltrimethylammonium chloride adsorbed onto silver electrodes from water and dimethylformamide [208]. In all cases progressive structural changes were concluded to occur with increasing surfactant adsorption. 

Other useful solid-state electrodes are based on silver compounds (particularly silver sulfide). Silver sulfide is an ionic conductor, in which silver ions are the mobile ions. Mixed pellets containing Ag2S-AgX (where X = Cl, Br, I, SCN) have been successfiilly used for the determination of one of these particular anions. The behavior of these electrodes is determined primarily by the solubility products involved. The relative solubility products of various ions with Ag+ thus dictate the selectivity (i.e., kt] = KSp(Agf)/KSP(Aw)). Consequently, the iodide electrode (membrane of Ag2S/AgI) displays high selectivity over Br- and Cl-. In contrast, die chloride electrode suffers from severe interference from Br- and I-. Similarly, mixtures of silver sulfide with CdS, CuS, or PbS provide membranes that are responsive to Cd2+, Cu2+, or Pb2+, respectively. A limitation of these mixed-salt electrodes is tiiat the solubility of die second salt must be much larger than that of silver sulfide. A silver sulfide membrane by itself responds to either S2- or Ag+ ions, down to die 10-8M level. 

Birss VI, Wright GA (1982) The potentiodynamic formation and reduction of a silver sulfide monolayer on a silver electrode in aqueous sulfide solutions. Electrochim Acta 27 1-7... 

Methods 1 and 2 are commonly used in environmental analysis. Method 3 uses a silver electrode to indicate the end point of potentiometric titration of dissolved sulfide with standard AgN03. The electrode response is slow. 

Other useful solid-state electrodes are based on silver compounds (particularly silver sulfide). Silver sulfide is an ionic conductor, in which silver ions are the mobile ions. Mixed pellets containing Ag2S-AgX (where X = Cl, Br,... 

The potentiometric determination of cyanide using ion selective electrodes has become yet another very popular technique, because it is convenient, rapid, and sensitive method of analysis (Frant et al, 1972). Microdiffusion of biological samples containing cyanide is recommended prior to potentiometric determination. The use of a cyanide ion-selective electrode in combination with the Conway microdiffusion method for the measurement of cyanide concentrations in human red blood cells and plasma was reported with remarkable recovery of cyanide (Yagi et al, 1990). Ion chromatographic determination of sulfide and cyanide in real matrices by using pulsed amperometric detection on a silver electrode was reported by Giuriati et al. (2004). 

Giuriati, C., Cavalli, S., Gomi, A., Badacco, D., Pastore, P. (2004). Ion chromatographic deteimination of sulfide and cyanide in real matrices by using pulsed amperometric detection on a silver electrode. J. Chromat. A. 1023 105-12. 

Many porous ion exchange membranes with high cation or anion selectivity have been described (B3, P13, S18). Sparingly soluble crystalline materials have been used as anion sensors, the membrane consisting of single crystals or pressed pellets often embedded in a vulcanized silicone rubber matrix. Examples include electrodes for fiuoride (LaF), sulfide (silver-silver sulfide), iodide, and sulfate. These probably function as... 

The chief restriction of these mixed-salt electrodes is that the solubility of the second salt must be much larger than that of Ag2S but, on the other hand, it must be sufficiently insoluble that its dissolution does not limit to relatively high values the test ion concentration that can be detected. As long as the membrane contains sufficient silver sulfide to provide silver ion conducting pathways through the membrane, it will function as a silver electrode. The potential, then, is related... 

Iodide in solution was determined by means of a piezoelectric crystal with silver electrodes connected to a normal TTL oscillator (104). In a follow-up- study (105), iodide was determined in the range 0.5 - 7 jM by electrodeposition on the silver electrodes of a crystal. Thiosulfate, cyanide, sulfide, Fe(III), Hg(II), and Ag interfered, but procedures to eliminate their interferences were described. 

The types of elements that can be determined by cathodic deposition at mercury electrodes are the amalgam-formers—Cu, Pb, Cd, Bi, Sn, Zn, Tl, and so forth. Using anodic deposition, halides and various sulfides can be determined at mercury electrodes, iodide at silver electrodes, and lead (as PbOa) and iron (as FegOg) at various solid electrodes. 

Other crystalline solid-state electrodes are commercially available to measure chloride, bromide, iodide, cyanide, and sulfide anions. Most of these electrode membranes are made from the corresponding silver salt mixed with silver sulfide, due to the low solubility of most silver salts in water. In addition, mixtures of silver sulfide and the sulfides of copper, lead, and cadmium make solid-state electrodes for Cu, Pb, and Cd " " available. An advantage of the silver sulfide-based electrodes is that a direct connection can be made to the membrane by a silver wire, eliminating the need for electrolyte filling... 

Another example in food analysis is the use of solid state copper and silver electrodes for evaluation of meat freshness. This is due to the change of put-rescine and dimethyl sulfide, the concentration of which changes during meat putrefaction. Such applications indicate the variety of applications of ISEs in food control and analysis. 

Although the HMDE is the most commonly used working electrode for CSV, the applications of other types of electrode materials have been reported. For example, silver electrodes have been used for the CSV determination of halides and sulfides. In addition, the use of carbon and platinum electrodes has been reported for metal cation determinations, including iron(II), cerium(in), manganese(II), thalliu-m(I), and lead(II). Such CSV measurements involve the precipitation of insoluble metal hydroxides on the electrode surface during the precipitation step. The drawback of the use of solid electrode materials is the poor reproducibility of the analysis and the low sensitivity, as a result of irregularities on the electrode surface and irreversible reduction of hydroxides (in the case of metals). 

Determination of hydrogen sulfide. The determination of hydrogen sulfide produced in the reactions was performed with an Orion Sulfide/Silver ion selective electrode connected to an Orion digital pH/mV meter. The electrode includes a silver/sulfide sensing element which develops an electrode potential in contact with a solution containing either silver or sulfide ions. The measured potential corresponding to the level of silver or sulfide ions in solution is described by the Nemst equation ... 

Hypochlorite, ascorbate, hydrazine, arsenite, thiosulfate, nitrite, nitrate, cobalt and iron are a partial list of the ions that have been detected using amperometric detection [55]. The most common ions determined by amperometric detection in 1C include inorganic anions forming complexes with cyanide, sulfide, and iodide at a silver electrode [56]. The relevant chemical reaction is shovra below. 

LPR testing is typically done in accordance with ASTM Standard G 96. Yeske [154] measured the corrosion rates of carbon steels in alkaline sulfide environments using the LPR technique and described the use of the silver/silver sulfide reference electrode. These techniques were develop>ed further by Crowe and Yeske [755] and used with real mill liquors for on-line monitoring of corrosion rates. The corrosion rates were found to be related to liquor composition with a strong flow effect. Crowe [156] also used LPR testing for on-line corrosion monitoring in white liquor clarifiers. Leinonen et al. [757] used the LPR method to monitor corrosion in a batch digester. 

Electrochemical corrosion monitoring in batch [157,161] and continuous digesters [162] has been accomplished using reference electrode probes that permit the measurement of the corrosion potential. The corrosion potential of the digester wall has been measured with respect to molybdenum, stainless steel, and silver/silver sulfide reference electrodes. Pawel et al. [763] have used electrochemical noise to monitor corrosion in a continuous digester. 

Potentiometric method with silver electrode probe and titration of sulfides at a —700 mVj level and of mercaptans at a —200 mV level (Fig, 8). 

Cathodic stripping voltammetry (CSV) is the inverse of ASV. Mercury electrodes can be used to detect and quantify species that form sparingly soluble mercury salts such as halide ions, sulfide, cyanide, thiols, and penicillins. CSV is not restricted to mercury electrodes. Any electrode material that, on oxidizing, forms sparingly soluble salts will work, such as silver electrodes for the determination of halide ions. Another possibility is that the ion of interest oxidizes to form a precipitate on the electrode surface. 

The hydrogen sulfide-free sample is dissolved in an alcoholic sodium acetate titration solvent and titrated potentiometiically with sQver nitrate solution, using as an indicator the potential between a glass reference electrode and a sUver/sUver-sulfide indicating electrode. Under these conditions, the mercaptan sulfur is precipitated as silver mercaptide and the end point of the titration is shown by a huge change in ceD potential. 

V. a term used to describe a voltage difference between one electrode and another VCDT. Vienna canyon diabolo troilite (actually silver sulfide used as a replacement standard for CDT [sulfur isotopes])... 

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