Oxidation with heavy metal ions

In addition to oxidation, sulfhydryl groups may react with heavy metal ions such as lead, iron, or copper. Principal sources of these heavy metals... 

Incompatible with oxidizing agents, heavy metal ions, especially copper and iron, methenamine, sodium nitrite, sodium salicylate, and theobromine salicylate. The aqueous solution is reported to be incompatible with stainless steel filters. ... 

Various precautions should be taken during manufacture and storage to minimise oxidation. The oxygen in pharmaceutical containers should be replaced with nitrogen or carbon dioxide contact of the drug with heavy-metal ions such as iron, cobalt or nickel, which catalyse oxidation, should be avoided and storage should be at reduced temperatures. 

Write equations for a thiol reaction with heavy metal ions and the production of disulfides that results when thiols are oxidized. (Section 3.9)... 

Finally, among occasionally chosen approaches in analysis of samples with heavy metal ions, one can quote, for example, simultaneous determination with metalloid(s), detection in flowing streams (FIA and HPLC see references (69-71) and references therein), use of hydrodynamic mode with rotated disc electrodes (RDEs) for improvement of accumulation (see references (11, 22, 23) in Table 5.1), array of microelectrodes and some indirect methods like an orientation assay for natural waters heavily polluted with mercury, when the measurement relies upon the decrease of the signal of a special marker—here, the [B(C5H6)4] anion—whose quite sensitive oxidation is suppressed by concurrent reaction with Hg V ... 

Metals and Metallic Ions. Under appropriate conditions, ozone oxidizes most metals with the exception of gold and the platinum group. When oxidized by ozone, heavy metal ions, such as Fe and Mn , result in the precipitation of insoluble hydroxides or oxides upon hydrolysis (48—50). Excess ozone oxidizes ferric hydroxide in alkaline media to ferrate, and Mn02 to MnO. ... 

Another method employed is the treatment of aqueous solutions of aminophenols with activated carbon (81,82). During this procedure, sodium sulfite, sodium dithionite, or disodium ethylenediaminotetraacetate (82) is added to increase the quaUty and stabiUty of the products and to chelate heavy-metal ions that would catalyze oxidation. Addition of sodium dithionite, hydrazine (82), or sodium hydrosulfite (83) also is recommended during precipitation or crystallization of aminophenols. 

Impurities, such as heavy metal ions, accelerate the decompn and may cause an expln to occur at a lower temp. Open Cup flash pt is 105°F (Ref 12). Since the material is an extremely powerful oxid agent it must be handled with extreme caution and kept away from combustible mats (Ref 12)... 

The most important point during sample preparation is to prevent oxidation of ascorbic acid. Indeed, it is easily oxidized by an alkaline pH, heavy metal ions (Cu and Fe ), the presence of halogens compounds, and hydrogen peroxide. The most suitable solvent for this purpose is metaphosphoric acid, which inhibits L-ascorbic oxidase and metal catalysis, and it causes the precipitation of proteins. However, it can cause serious analytical interactions with silica-based column, e.g., C18 or amino bonded-phases [542] and it could co-elute with AA. 

Considering first adsorption of metal ions or neutral species directly on the snbstrate, there are a nnmber of possible mechanisms for this process. Most simply, there will an equilibrinm between metal species in solution and a solid snr-face leading to dynamic adsorption of the metal. Adsorption of metal ions onto solid snrfaces has been extensively studied, to a large extent becanse of the nse of oxide snrfaces to adsorb heavy metal ions and remove them from solntion (see Ref. 55 for an example and list of other references on this snbject). This adsorption may go even farther with ion exchange between the solntion metal ions and ions in the substrate (again, glass is a good example of where this may occnr). 

Chromium(IV) and chromium(V), previously encountered as the oxides and halides and as unstable intermediates in solution, are now represented by complexes of ligands stabilized by heavy substitution against oxidation by the metal ion, and oxo and nitrido derivatives. These remain unimportant oxidation states compared with molybdenum and tungsten. 

The reaction is catalyzed by divalent heavy metal ions, especially by Cu2+ and Co2+. It follows zeroth order, so it is independent of the concentration of the reactants Na2S03 and 02( ) but only depends on the rate of mass transfer. The remaining sulfite is oxidized to sulfate by the addition of iodine and the iodide generated is back-titrated with thiosulfate [Eqs. (8.37), (8.38)]. 

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