Sulfides analysis

The LC-LC configuration has been applied to sulfide analysis in a variety of different matrices, as well as for acetate and trifluoroacetate analysis in peptides (as shown in Figure 5.5). 

Aconitase was the third protein and the first enzyme for which a 3Fe cluster was postulated by Mbssbauer spectroscopy (Kent et al., 1982) the meticulous inorganic sulfide analysis by Beinert et al. (1983) established the composition of this class of cluster as 3Fe 4S. Although the 3Fe form of the protein is inactive, it can be reactivated by the addition of Fe " under anaerobic reducing conditions (Kennedy et al., 1983). The resulting cluster was shown by Mbssbauer spectroscopy to be similar to ferre-doxin 4Fe 4S clusters in the +2 oxidation state the more reduced cluster was only 30% active. Mbssbauer spectroscopy also indicated that... 

Meissner, D., Benndorf, C., Memming, R. 1987a. Photocorrosion of cadmium sulfide analysis by photoelectron spectroscopy. Appl. Surf. Sci., 1987, 27, 423 136. 

Used as a chlorinating agent and as an oxidant (e. g., in sulfide analysis), in the form of a 25-35% solution of ICI3 in concentrated hydrochloric acid. 

Silver sulfide is an excellent material for a solid-state electrode. It has very low solubiHty and consequently there are only few potentiometric interferences (CN , Hg ). It can be easily compressed into mechanically stable pellets and it is also accessible as single crystal for electrodes. At ambient conditions (below 176°C) its monoclinic p-modification, acanthite, is stable, and shows high ionic conductivity due to silver ions. Silver sulfide electrodes respond to both silver and sulfide ions with good practical detection limits (10 -lO moll ) in Nernstian manner. Sulfide analysis is performed in strongly alkaline solutions. 

R. Redondo, V.C. Machado, M. Baeza, J. Lafuente, D. Gabriel, On-line monitoring of gas-phase bioreactors for biogas treatment hydrogen sulfide and sulfide analysis by automated flow systems. Anal. Bioanal. Chem. 391 (2008) 789-798. 

In addition to analyses for CAA, other analyses that require different preservation steps may be desired. Listed below are the most common analyses and the preservation steps that they require also, see lists in Lico et al. (1982). Samples for chemical oxygen demand and total organic carbon should be treated with 2 ml of concentrated H2SO4 per liter of sample. Samples for phenols should have Ig of copper sulfate added per liter of sample, and then should be acidified to pH 4 with phosphoric acid. Samples for dissolved metals should have 3 ml of 1 1 nitric acid added per liter of sample. Samples for sulfide analysis should have 2ml of zinc acetate added per liter of sample. Samples for nonmetal anions and sulfate analysis need no treatment. 

Inorganic Analysis The most important precipitants for inorganic cations are chromate, the halides, hydroxide, oxalate, sulfate, sulfide, and phosphate. A summary of selected methods, grouped by precipitant, is shown in Table 8.1. Many inorganic anions can be determined using the same reactions by reversing the analyte... 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

Like the refining of the PGMs, the analysis is compHcated by the chemical similarity of the metals. The techniques used depend on the elements present and their concentration in the sample. For some low grade samples, analysis is preceded by a concentration stage using fire assay with collection into a lead or nickel sulfide button. The individual metals can then be determined. 

A double end point, acid—base titration can be used to determine both sodium hydrosulfide and sodium sulfide content. Standardized hydrochloric acid is the titrant thymolphthalein and bromophenol blue are the indicators. Other bases having ionization constants in the ranges of the indicators used interfere with the analysis. Sodium thiosulfate and sodium thiocarbonate interfere quantitatively with the accuracy of the results. Detailed procedures to analyze sodium sulfide, sodium hydro sulfide, and sodium tetrasulfide are available (1). 

Hydrogen sulfide causes the precipitation of sulfides from many heavy-metal salts. The classical quaUtative analysis scheme depends on precipitation of the sulfides of Hg, Pb, Bi, Cu, Cd, As, Sb, and Sn under acid conditions and the sulfides of Co, Ni, Mn, Zn, and Fe under ammoniacal conditions. 

An ion-selective electrode is available for chloride analysis chloride can be measured potentiometrically at 10 -1 M. Iodide and sulfide are the principal interferences. 

The heavy metal salts, ia contrast to the alkah metal salts, have lower melting points and are more soluble ia organic solvents, eg, methylene chloride, chloroform, tetrahydrofiiran, and benzene. They are slightly soluble ia water, alcohol, ahphatic hydrocarbons, and ethyl ether (18). Their thermal decompositions have been extensively studied by dta and tga (thermal gravimetric analysis) methods. They decompose to the metal sulfides and gaseous products, which are primarily carbonyl sulfide and carbon disulfide ia varying ratios. In some cases, the dialkyl xanthate forms. Solvent extraction studies of a large number of elements as their xanthate salts have been reported (19). 

Ion-selective electrodes are available for the electro analysis of most small anions, eg, haUdes, sulfide, carbonate, nitrate, etc, and cations, eg, lithium, sodium, potassium, hydrogen, magnesium, calcium, etc, but having varying degrees of selectivity. The most successful uses of these electrodes involve process monitoring, eg, for pH, where precision beyond the unstable reference electrode s abiUty to deUver is not generally required, and for clinical apphcations, eg, sodium, potassium, chloride, and carbonate in blood, urine, and semm. 

Oxides (Ln Oj), fluorides (LnF ), sulfides (Ln S, LnS), sulfofluorides (LnSF) of lanthanides are bases of different functional materials. Analytical control of such materials must include non-destructive methods for the identification of compound s chemical forms and quantitative detenuination methods which does not require analytical standards. The main difficulties of this analysis by chemical methods are that it is necessary to transform weakly soluble samples in solution. 

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