Potentiometry silver

Potentiometry Silver chloride electrodes as well as membrane electrodes with ion exchange or ion carrier are used for chloride determinations. Measurements are usually performed with a highly diluted sample to obtain its chloride concentration. The measurement of chloride activity in undiluted samples is used more and more often, as it is easily performed by combined blood gas/electrolyte analyzers. 

It is also possible in appropriate cases to measure by direct potentiometry the concentration of an ion which is not directly concerned in the electrode reaction. This involves the use of an electrode of the second kind , an example of which is the silver-silver chloride electrode which is formed by coating a silver wire with silver chloride this electrode can be used to measure the concentration of chloride ions in solution. 

Sediment Trap in silver nitrate. Potentiometry/ ion-selective electrode No data NR Allen et al. 1994... 

Sodium valproate has been determined in pharmaceuticals using a valproate selective electrode [13,14]. The electroactive material was a valproate-methyl-tris (tetra-decyl)ammonium ion-pair complex in decanol. Silver-silver chloride electrode was used as the reference electrode. The electrode life span was >1 month. Determination of 90-1500 pg/mL in aqueous solution by direct potentiometry gave an average recovery of 100.0% and a response time of 1 min. 

A schematic diagram of a typical pH electrode system is shown in Fig. 10.1. The cell potential, i.e. the electromotive force, is measured between a pH electrode and a reference electrode in a test solution. The pH electrode responds to the activity or concentration of hydrogen ions in the solution. The reference electrode has a very stable half-cell potential. The most commonly used reference electrodes for potentiometry are the silver/silver chloride electrodes (Ag/AgCl) and the saturated calomel electrodes (SCE). 

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. 

The ISEs described in this section are useful primarily for determination of halide ions by direct potentiometry, where the silver halide in the membrane is identical with the determinand. As follows from the discussion on p. 48 an electrode made of a less soluble silver halide X can be used to determine other halide Y" if the condition... 

The potentiometric method has been used for the determination of pure procaine base or its hydrochloride salt, and for procaine in pharmaceutical formulations. Lemahieu and Resibois reported the potentiometric determination of procaine hydrochloride with silver nitrate in dimethyl sulfoxide [64], Procaine was potentiometrically analyzed using a procaine-selective membrane electrode [65]. Abou-Ouf et al. have used potentiometry to determine procaine and other drugs in ointments and creams with dibromohydantoins [66]. 

The use of equation (3.2) to study the behaviour of catalysts is known as solid electrolyte potentiometry (SEP). Wagner38 was the first to put forward the idea of using SEP to study catalysts under working conditions. Vayenas and Saltsburg were the first to apply the technique to the fundamental study of a catalytic reaction for the case of the oxidation of sulfur dioxide.39 Since then the technique has been widely used, with particular success in the study of periodic and oscillatory phenomena for such reactions as the oxidation of carbon monoxide on platinum, hydrogen on nickel, ethylene on platinum and propylene oxide on silver. 

A demonstration of potentiometry with a silver electrode (or a microscale experiment for general chemistry) is described by D. W. Brooks, D. Epp, and H. B. Brooks, Small-Scale Potentiometry and Silver One-Pot Reactions, ... 

With very few exceptions, quantitative epoxide assay techniques currently in use are derived from the reeotion of ethylene oxides with halogen adds, notably hydrochloric acid and hydrobromio add, in a variety of solvents. Acid uptake may be determined by any of several reliable procedures. These include titration with standard base8 nr back-titration with standard acid.744 The end-point may be detected visually in the presence of suitable acid-base indicators, or by the more precise technique of potontionaetry.447.4 -470 A useful alternative, applicable in the presence of easily hydrolysed substances or of amines that buffer the end-point, is the technique of argentiometry. In this procedure excess of halide ion is titrated with silver nitrate in tV presence of ferric thiocyanate indicator,470 1884 or potentiometri-cally.188 ... 

Table 5), and several are now being used, or are potentially useful, for measuring key ocean elements. The most common use of direct potentiometry (as compared with potentiometric titrations) is for measurement of pH (Culberson, 1981). Most other cation electrodes are subject to some degree of interference from other major ions. Electrodes for sodium, potassium, calcium, and magnesium have been used successfully. Copper, cadmium, and lead electrodes in seawater have been tested, with variable success. Anion-selective electrodes for chloride, bromide, fluoride, sulfate, sulfide, and silver ions have also been tested but have not yet found wide application. 

S) Bishop, E., and R. G. Dhaneshwar Differential Electrolytic Potentiometry. VIII. The Behaviour and Energetics of Current-Carrying Silver and Silver Halide Electrodes in the Semi-Micro Scale Titration of Nanogram Amounts of Halides at Extreme Dilution. Analyst 87, 845 (1962). 

When voltammetry measurements are made in nonaqueous solvents, the problems of an adequate reference electrode are compounded. Until the 1960s the most common reference electrode was the mercury pool, because of its convenience rather than because of its reliability. With the advent of sophisticated electronic voltammetric instrumentation, more reliable reference electrodes have been possible, especially if a three-electrode system is used. Thus, variation of the potential of the counter electrode is not a problem if a second non-current-canying reference electrode is used to monitor the potential of the sensing electrode. If three-eleetrode instrumentation is used, any of the conventional reference electrodes common to potentiometry may be used satisfactorily. Our own preference is a silver chloride electrode connected to the sample solution by an appropriate noninterfering salt bridge. The one problem with this system is that it introduces a junction potential between the two solvent systems that may be quite large. However, such a reference system is reproducible and should ensure that two groups of workers can obtain the same results. 

Figure 20-3. Potentiometrie titration curve of chloride titrated with silver ion.

NB Very careful workusing hydrogen and silver-silver chloride half cells. Also reported acetic acid pXa = 4.754, cf. Acetic acid, no. 12 (above), pKg = 4.756 by conductance and potentiometry. 

For a reference electrode we choose one of the well-established reference electrodes used in potentiometry, eg saturated calomel electrode (SCE), silver-silver chloride electrode. Such electrodes have a stable potential and a small temperature dependence of potential. The saturated calomel electrode is almost always the reference electrode used for aqueous solution dc polarography. 

Compare this equation with Eqs. (15.7) and (15.15). By convention, the reference electrode is connected to the negative terminal of the potentiometer (the readout device). The common reference electrodes used in potentiometry are the SCE and the silver/silver chloride electrode, which have been described. Their potentials are fixed and known over a wide temperature range. Some values for these electrode potentials are given in Table 15.3. The total cell potential is measured experimentally, the reference potential is known, and therefore the variable indicator electrode potential can be calculated and related to the concentration of the analyte through the Nemst equation. In practice, the concentration of the unknown analyte is determined after calibration of the potentiometer with suitable standard solutions. The choice of reference electrode depends on the application. For example, the Ag/AgCl electrode cannot be used in solutions containing species such as halides or sulfides that will precipitate or otherwise react with silver. 

Kinetic of the reaction was studied by potentiometry with the use of the ion-selective microelectrode ELIS- 3 Silver. The concentration of the silver ions was determined continuous during the reaction proceeding per change of the potential of the ion-selective electrode regarding to the chlorine-silver comparison electrode. 

Modern potentiometry with variety of classical and membrane sensing electrodes has, so far, rather occasionally been used in ion-chromatography. The first applications of poten-tiometric detection appeared in mid-seventies, when it was utilized for very sensitive detection of halide with silver/silver chloride electrode, and nitrate and nitrite with liquid-state membrane nitrate electrode.In later works number of indicating electrodes used for po-tentiometric detection has significantly increased. A list of reported applications is shown in Table 1. 

Potentiometry For sodium determinations by potentiometry, a glass electrode is usually used, but ion-carrier or ion-exchange membranes are also feasible for the ISE. A silver/silver chloride or a calomel electrode is used as the reference electrode. 

Metallic silver-wire electrode Potentiometry 0.05-250 mg CN Gas-diffusion/use of a non-seleclive sensor... 

A/,AFdioctadecyl- methylamine Potentiometry pH 4.0-11.0 The ionophore was photo-cured on a silver wire... 

Compare this equation with Equations 15.7 and 15.15. By convention, the reference electrode is connected to the negative terminal of the potentiometer (the readout device). The common reference electrodes used in potentiometry are the SCE and the silver/silver chloride electrode, which have been described. Their potentials are fixed and known over a wide temperature range. Some values for these electrode potentials are given in Table 15.3. The total cell potential is measured... 

In a direct potentiometric measurement, we use an electrode such as a silver wire to measure [Ag ] or a pH electrode to measure [H" ] or a calcium ion-selective electrode to measure [Ca " ]. There is inherent inaccuracy in most direct potentiometric measurements because there is usually a liquid-liquid junction with an unknown voltage difference making the intended indicator electrode potential uncertain. For example. Figure 15-5 shows a 4% standard deviation among 14 measurements by direct potentiometry. Part of the variation could be attributed to differences in the indicator (ion-selective) electrodes and part could be from varying liquid junction potentials. 

A limited amount of electroanalytical work has been done in sulfate melts. The oxygen electrode has been mentioned above for alkaline melts. In 1961, Liu (77,78) applied potentiometry, chronopotentiometry and coulometric titrations in lithium sulfate-potassium sulfate melts at 625°C using a silver reference electrode. An electromotive force series of limited scope and... 

The so-called zero-point titration also gained application in water analysis [21]. In this method, the potential difference between two identical indicator electrodes (e.g., two silver wire electrodes) is followed. One of them is in a half cell containing solution corresponding to the equivalence point of the titration, and the other one is dipped into the sample-containing titration vessel. The silver nitrate reagent (0.01 M) is added as long as potential difference exists. With this zero-point potentiometry a determination limit as low as 1.3 mg/dm can be achieved. 

The constant-current potentiometry is another endpoint detection technique that can be used in the titrations of very dilute chloride sample [22-24], In this case, two silver metal or chloride-coated silver indicator electrodes are used dipping into the intensively stirred titration vessel. A well-stabilized constant, low intensity current is forced between the two electrodes and the potential difference is measured between them. The titration endpoint is very sharp in this case even at very low concentration. 

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