Cyanide ISE

Cyanide ion-selective electrode As demonstrated in chapter 3.4, the dissolution of a halide ISE in the presence of some complexing agents, especially cyanide, can be used for determination of these agents [312, 392, 434]. An iodide ISE can be used as a cyanide ISE. The principal application of this electrode is in the determination of cyanides in waters [60, 126, 281, 336] and in galvanic baths [222, 225]. 

SCN + SO . The decrease in the cyanide concentration is then monitored using a cyanide ISE and the rate constant of the reaction is proportional to the rhodanase activity [174, 238]. 

I recollect very elegant research starting fixtm Prof. G. Rechnitz involving the development of an amygdaline sensor based on the coupling of an Ion Selective Electrode (cyanide ISE) tvith betaglucosidase to give benzaldeyde and cyanide. ... 

As summarised in Table 3.4, some electroanalytical methods have been certified by standardisation bodies for the chemical characterisation of ambient water samples, mostly in the class of inorganic substances. Conductometric detection is used in direct method for ionic constituents and also as chromatographic detector for individual cations and anions. Total, inorganic and organic carbon in water can be also assayed by conductometric detection. Amperometric detection has been certified for dissolved oxygen and cyanide. ISE potentiometry is used for standardised measurements of a set of ions and also for the evaluation of water oxidation-reduction potential. Voltammetric detection is the base for diverse methodologies oriented to the determination of trace elements including the most relevant elemental pollutants. 

Many IC techniques are now available using single column or dual-column systems with various detection modes. Detection methods in IC are subdivided as follows [838] (i) electrochemical (conductometry, amper-ometry or potentiometry) (ii) spectroscopic (tJV/VIS, RI, AAS, AES, ICP) (iii) mass spectrometric and (iv) postcolumn reaction detection (AFS, CL). The mainstay of routine IC is still the nonspecific conductometric detector. A significant disadvantage of suppressed conductivity detection is the fact that weak to very weak acid anions (e.g. silicate, cyanide) yield poor sensitivity. IC combined with potentiometric detection techniques using ISEs allows quantification of selected analytes even in complex matrices. The main drawback... 

The above principles have been employed in the construction of a monitor of gaseous inorganic fluorine and chlorine compounds after absorption of the gases in a solution [13], a monitor of free cyanide [35] (fig. 5.9), and a monitor of sulphate using the reaction of the sulphate with a Pb standard solution and, following the decrease in the Pb concentration, with a Pb ISE [152] (fig. 

The Ag2 S ISE has Nemstian response dE/d log a( = 0.0296 V in the sulphide concentration range 10" to 10" M and silver ions from 10 to 10 M if the solutions are prepared from pure salts, as a further concentration decrease is prevented by adsorption on the glass (see p. 76 and [87, 163]). After prolonged use, the limit of the Nemstian behaviour shifts to about 10" m [130] as a result of formation of mixed potentials on accumulation of metallic silver in the membrane surface. An analogous deterioration in the membrane function in the presence of iodine results from surface oxidation [23]. Cyanide interferes only at large concentrations the equilibrium constant of the reaction... 

Table 12.6 sets out other standard methods for the determination of nonmetallic substances chloride is determined by titration,50 51 73 VIS spectrophotometry,50 74 and ISE 51 chlorine by titration and VIS spectrophotometry 75-77 fluoride by VIS spectrophotometry50 and ISE 50 78 79 iodide by VIS spec-trophotomtery 50 cyanide by titration, VIS spectrophotometry, and ISE 50 80 81 sulfate by gravimetry50 51 and turbidimetry 50 sulfite by titration and VIS spectrophotometry 51 and sulfur by titration and VIS spectrophotometry.50 51... 

Many of the UV-VIS spectrophotometric methods (shown in Tables 12.3 and 12.6) have been automated by using flow analyzers. Thus, nitrite and nitrate,50,82 ammonium,50,83 orthophosphate,50,84,85 silicates,50,86 chloride,50,87 cyanide,50,88 and sulfate50,89 are measured by CFA and FIA. Oxygen is measured by iodometric titration51,90 and electrochemical methods91 (Table 12.7). Other dissolved gasses (Table 12.2) are measured by ISE-based gas sensors. 

Linear relation between peak height and concentration was also found in chromatographic detection with Ag/AgCl electrode, with sulphide ISE used for cyanide... 

The potentiometric detection of the endpoint of precipitation titrations is very often used because not many visual indicators are available, in particular when mixtures of analytes are titrated. Halides, cyanide, sulfide, chromate, mercaptans, and thiols can be titrated with silver nitrate, using the silver sulfide-based ISE. Also complex mixtures, such as sulfide, thiocyanide, and chloride ions, or chloride, bromide, and iodide ions, can be titrated potentio-metrically with silver(I) ions. When the solubility of a compound formed during titration is too high, nonaqueous or mixed solvents are used, for example,... 

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