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Trace metal ion

Quigley, M. N. Vernon, E. Determination of Trace Metal Ion Concentrations in Seawater, /. Chem. Educ. 1996, 73, 671-675. [Pg.449]

In natural water, the half-hves fall between these extremes. For example, the half-life of Lake Zbrich water (pH 8, 1.5 meq/LHCO ) is 10 min (27). The decomposition in natural water also can be initiated by trace metal ions, eg, Fe , promoted by impurities such as organic matter, and inhibited by HO radical scavengers, eg, HCO3, COg , HPO (25,28). [Pg.491]

Chelants at concentrations of 0.1 to 0.2% improve the oxidative stabiUty through the complexation of the trace metal ions, eg, iron, which cataly2e the oxidative processes. Examples of the chelants commonly used are pentasodium diethylenetriarninepentaacetic acid (DTPA), tetrasodium ethylenediarninetetraacetic acid (EDTA), sodium etidronate (EHDP), and citric acid. Magnesium siUcate, formed in wet soap through the reaction of magnesium and siUcate ions, is another chelant commonly used in simple soap bars. [Pg.158]

Medical Uses. Citric acid and citrate salts are used to buffer a wide range of pharmaceuticals at their optimum pH for stabiUty and effectiveness (65—74). Effervescent formulations use citric acid and bicarbonate to provide rapid dissolution of active ingredients and improve palatabiUty. Citrates are used to chelate trace metal ions, preventing degradation of ingredients. Citrates are used to prevent the coagulation of both human and animal blood in plasma and blood fractionation. Calcium and ferric ammonium citrates are used in mineral supplements. [Pg.185]

The decomposition to sulphate and oxygen is subject to trace metal-ion catalysis . Co(II) , Mo(VI) and Mn(II) are particularly effective, but the kinetics could not be resolved unequivocally in all cases. The rate expressions are... [Pg.482]

The majority of LCEC applications have used oxidative detection. This is likely because of the perceived difficulties encountered with reductive detection. In particular, dissolved oxygen and trace metal ions must be removed to prevent high background currents. These problems are not difficult to overcome and more applications of reductive detection should appear as this is more generally realized. [Pg.26]

The detection and quantification of one or more of the above lipid peroxidation produas (primary and/or secondary) in appropriate biofluids and tissue samples serves to provide indices of lipid peroxidation both in ntro and in vivo. However, it must be stressed that it is absolutely essential to ensure that the products monitored do not arise artifactually, a very difiScult task since parameters such as the availability of catalytic trace metal ions and O2, temperature and exposure to light are all capable of promoting the oxidative deterioration of PUFAs. Indeed, one sensible precaution involves the treatment of samples for analysis with sufficient levels of a chainbreaking antioxidant [for example, butylated hydroxy-toluene (BHT)] immediately after collection to retard or prevent peroxidation occurring during periods of storage or preparation. [Pg.14]

The autoxidation of aldehydes, and of other organic compounds, may be lessened considerably by very careful purification—removal of existing peroxides, trace metal ions, etc.—but much more readily and effectively by the addition of suitable radical inhibitors, referred to in this context as anti-oxidants. The best of these are phenols and aromatic amines which have a readily abstractable H atom, the resultant radical is of relatively low reactivity, being able to act as a good chain terminator (by reaction with another radical) but only as a poor initiator (by reaction with a new substrate molecule). [Pg.330]

Riccardo et al. [841] showed that chitosan is promising as a chromatographic column for collecting traces of transition elements from salt solution and seawater, and for recovery of trace metal ions for analytical purposes. Traces of transition elements can be separated from sodium and magnesium, which are not retained by the chitosan. [Pg.288]

Identify potential reaction contaminants. In particular, consider possible contaminants, which are ubiquitous in a plant environment, such as air, water, rust, oil, and grease. Think about possible catalytic effects of trace metal ions such as sodium, calcium, and others commonly present in process water. [Pg.26]

Model Studies. In model studies of adsorption, one deals with simple, well-defined systems, where usually a single well-characterized solid phase is used and the composition of the ionic medium is known, so that reactions competing with the adsorption may be predicted. It is not a trivial problem to compare the results from such model studies with those from field studies, or to use model results for the interpretation of field data. In field studies, a complex mixture of solid phases and dissolved components, whose composition is only poorly known, has to be considered competitive reactions of major ions and trace metal ions for adsorption may take place, and the speciation of the trace metal ions is often poorly understood. In order to relate field studies to model studies, distribution coefficients of elements between the dissolved and solid phases are useful. These distribution coefficients are of the following form ... [Pg.370]

Information on the nature of the chemical environment of trace metal Ions adsorbed on clay minerals can be obtained by a number of spectroscopic methods, but the principal applications have used either XPS or ESR spectroscopy, or one of its related techniques, such as ENDOR and ESEM spectroscopy. [Pg.348]

C. Chemical Interactions in Solution. The rather dramatic effect of trace metal ions and additives on electrodeposition was reviewed briefly in the previous sections for copper and zinc. [Pg.711]

Figure 3.7 Test for trace metal ions on the surface of octadecyl-bonded silica gel. Column A, 5 pm octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. B, octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. C, octadecyl-bonded 10 pm silica gel, 30 cm x 4.0 mm i.d. eluent, 50% aqueous acetonitrile flow rate, 1 ml min-1 temperature, ambient detection, UV 220 nm (the scales of A, B, and C are not the same) sample, 8-hydroxyquinoline. Columns, A, metal ion free B, low proportion of metal ions C, high level of metal ions. Figure 3.7 Test for trace metal ions on the surface of octadecyl-bonded silica gel. Column A, 5 pm octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. B, octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. C, octadecyl-bonded 10 pm silica gel, 30 cm x 4.0 mm i.d. eluent, 50% aqueous acetonitrile flow rate, 1 ml min-1 temperature, ambient detection, UV 220 nm (the scales of A, B, and C are not the same) sample, 8-hydroxyquinoline. Columns, A, metal ion free B, low proportion of metal ions C, high level of metal ions.
The use of impregnated resins in the preconcentration and separation of trace metal ions provides the following advantages ... [Pg.575]

It is known that relatively subtle solvent properties (. . the presence of trace metal ions or dissolved oxygen) can have a pronounced effect on Tj values (1 ). For this reason, we have emphasized studies based on comparing relative Tj values of resonances taken from the same spectrum of a given compound, rather than comparing absolute Tj values taken from different spectra. To insure reproducibility, duplicate Tj determinations were made in all cases. Monomer Tj values (e.g. methyl a-D-gluco-pyranoside) can be obtained in less than an hour. However, we have experienced difficulty in obtaining consistent absolute Tj values for successive samples of the same monosaccharide. Such reproducibility problems have not been observed for the polysaccharides, and we have observed no successive Tj value differences which can be attributed to solvent or sample preparation. [Pg.49]

Of the approximately 25 elements which are currently regarded as important if not essential for life, four can be classified as bulk metal ions Na, K, Mg, and Ca, and ten as trace metal ions Fe, Cu, Mn, Zn, Co, Mo, Cr, Sn, V and Ni. The nonmetallic elements are H, B, C, N, O, F, Si, P, S, Cl, Se and I. Over the past years, various evidence has been put forth concerning the roles of Cd, As, Pb, and A1 as potential trace elements. These metals play a wide range of functional and structural roles within human biochemistry. [Pg.481]

In all applications, the chelant may have been added for a variety of purposes. As discussed in Section 10.2, chelants can have roles where calcium and magnesium control is key, such as detergency or scale inhibition. Alternatively, transition metal ion control could be the target, for example, in bleach stabilization. Some applications require both properties simultaneously. Chelants can also act as biocide potentiators or as antioxidants, to prevent trace metal ions from causing oxidative spoilage. This may require that metal concentrations be kept below certain... [Pg.299]

The reactions of silver(I) with 1,5-diphenyl thiocarbazone (56 dithizone = HaDz) by comparison to thiosemicarbazones have been thoroughly investigated.442,444 Dithizone has for many years been used as a colorimetric reagent for trace metal ions. Its metal complexes are of two types, the so-called primary and secondary dithizonates. Primary dithizonates are generally formed at low pHs where the ligand becomes mono depronated (pA = 4.5) but retains the NH proton. Secondary dithizonates are formed in the presence of an excess of metal and/or at higher pH values where the ligand becomes fully deprotonated. Since it has been estimated that for free dithizone pK2 > 15, the second proton obviously becomes labilized in the presence of metal ions. [Pg.832]

T1he adsorption of metal ions from aqueous solutions is a phenomenon of immediate interest to workers in many diverse disciplines. The incorporation of metals into geological sediments, removal of metal ions from industrial and civic effluent, interference of trace metal ions in analytical and electroanalytical chemistry, ore flotation, metallurgical leaching processes, and the stability of ceramic slips are all processes which are controlled to a large extent by interaction of metal ions with solid-liquid interfaces. [Pg.70]


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See also in sourсe #XX -- [ Pg.1033 ]

See also in sourсe #XX -- [ Pg.162 , Pg.163 , Pg.164 , Pg.165 , Pg.166 , Pg.167 , Pg.168 , Pg.169 ]




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