Ascorbic acid, reductions with

Acetate, (reduction with) ascorbic acid + KI, citrate, V,V-dihydroxyethylglycine, EDTA, F , formate, NaOH + H2O2, oxidation to CrOJ , NagP30io, sulfosalicylate, tartrate, triethylam-ine, tiron... 

V (Reduction with) ascorbic acid, hydrazine, or NH2OH HCl, CN , EDTA, F , H2O2, manni-... 

Sometimes the metal may be transformed into a different oxidation state thus copper(II) may be reduced in acid solution by hydroxylamine or ascorbic acid. After rendering ammoniacal, nickel or cobalt can be titrated using, for example, murexide as indicator without interference from the copper, which is now present as Cu(I). Iron(III) can often be similarly masked by reduction with ascorbic acid. 

NH2OH HC1, NH3, NOt, 1,10-phenanthroline, S2-, SCN- + SO -, S20(-, sulfosalicylate, tartrate, thioglycolic acid, thiosemicarbazide, thiocarbohydrazide, thiourea Fe Acetylacetone, (reduction with) ascorbic acid, C2OJ-, citrate, CN-, 2,3-dimercaptopropanol,... 

Hg Acetone, (reduction with) ascorbic acid, citrate, Cl-, CN-, 2,3-dimercaptopropan-l-ol, EDTA,... 

Reduction with) ascorbic acid, hydrazine, or NH2OH HC1, CN-, EDTA, F-, H202, mannitol, oxidation to vanadate, triethanolamine, tiron Citrate, F-, H202, hydrazine, Na5P3O10, NH2OH HC1, oxalate, SCN-, tartrate, tiron, triphosphate, oxidation to tungstate(VI)... 

Olsen et al. [62] have described a method for the determination of pH8.5 sodium bicarbonate extractable phosphorus in soils. The concentration of the blue complex produced by the reduction, with ascorbic acid, of the phosphomolybdate formed when acid ammonium molybdate reacts with phosphate is measured spectrophotometrically at 880 nm [63]. 

Figure 2.8 Redox-driven translocation of a copper center, based on the Cu"/Cu change. The Cu11 ion stays in the tetramine compartment of the ditopic ligand 10, whereas the Cu1 ion prefers to occupy the bis-(2,2 -bipyridine) compartment. The translocation of the copper center between the two compartments is fast and reversible when carried out through the Cun-to-Cu1 reduction with ascorbic acid and Cu -to-Cu" oxidation with H202, in a MeCN solution.

Unsaturated 1,4-diketones are available from the corresponding nitro ketones by adsorption on silica gel," oxidation with peroxodisulfate or reduction with ascorbic acid (equation 38). 

The resultant tocopheroxyl radical is relatively stable and, in normal circumstances, insufficiently reactive to initiate lipid peroxidation itself. It has been demonstrated in vitro that a-tocopherol radical can be converted back to a-tocopherol by reduction with ascorbic acid at the surface of biological membranes... 

Figure 30. Photoinduced rotation, based on the use of an oxidant scavenger (/>-nitrobenzylbromide), of the terpyridine-containing macrocycle in the copper-containing [2] catenane 32+ [121]. The system is brought back to the initial structure through another ring rotation, induced chemically by reduction with ascorbic acid.

At pH 2.6, Th, Zr, Ti, Fe(III), Bi, In, Al, and Y (but not the lanthanides) interfere. Reducing the pH minimizes these interferences and even masks yttrium completely. Iron(III) and cerium(IV) are masked by reduction with ascorbic acid. Oxalate, sulphate, fluoride, and phosphate interfere in the determination of scandium. 

Figure 3. Effect of ethanol addition on the reduction rate of the Cu(II) complexes. Key O, reduction with Fe(II)-(phenanthroline)s , reduction with ascorbic acid.

Fig. 19. The redox-driven translocation of an iron center within a heteroditopic ligand containing a hard compartment [the tris(hydroxamate) donor set, lower level preferred by Fe(III)] and a soft compartment [tris(2, 2 -bipyridine) donor set, upper level chosen by the Fe(II) center). Chemical reduction (with ascorbic acid) and oxidation (with peroxydisulfate) make the iron center translocate from one level to the other...

Rb] center U.V./visible and CD spectroscopy show characteristic bands. Reduction with ascorbic acid can usually be accomplished. EPR has characteristic features at g = 4.3 readily observable at 77 K with additional signals at g = 9.4 at T < 20K, in the oxidized form. No signal is observed in the reduced state. 

Bromopyrazol-3-ones 157a-d (for a-d see Scheme 43) have been prepared by Spitulnik (85S299) from 4,4-dibromopyrazol-3-ones 155a-d (for a-d see Scheme 43) in two steps. First reduction with ascorbic acid to give monobromopyrazole salts 156a-d (for a-d see Scheme 43) followed by acidification (Scheme 50). 

The most important forms of phosphorus are inorganic orthophosphates which are determined photometrically with molybdenum. Orthophosphates react with ammonium molybdate in the presence of sulphuric acid and antimony ions to form heteropolyacids — phosphomolybdic acid. By reduction with ascorbic acid the yellow complex of phosphomolybdic acid changes into a solution of Phosphomolybdic Blue which can be determined photometrically ... 

Another method developed for the determination of iodide was GC—mass spectrometry (Mishra et al., 2000). Iodide was oxidated to iodine with 2-iodosobenzoate, and then converted into d-iodo-A. A dimethylanifine in the presence of A, A -dimethylanihne. The derivative was extracted into cyclohexane and determined by GC—mass spectrometry. The method could also be used to determine iodine by derivatization in the absence of 2-iodoso-benzoate, and iodate by its reduction with ascorbic acid to iodide and subsequent derivatization. The calibration graph was finear from 0.02 to 50p,g U of iodide with a correlation coefficient of 0.9998. The limit of detection was 8ng 1 of iodide. The proposed method was appfied to the determination of iodate in iodized table salt and free iodide and total iodine in seawater. The recovery was in the range of 96.8—104.3%, and the relative standard deviations were from 1.9% to 3.6%. A sample clean-up by solid-phase extraction with a LiChrolut EN cartridge was... 

The syntheses of 2-methyl-5,6-dihydroxyindole 11 (Scheme 2) and 3-methyl-5,6-dihydroxyindole 29 were achieved by Bu Lock and Harley-Mason (51JCS2248) and by Beer and co-workers (49JCS2061) through cyclization of appropriate 3,4-dihydroxyphenylalanine precursors. A simple preparation of indole 3 was reported by Mattok and Heacock (64CJC484) and involved the oxidation of adrenaline with potassium ferricyanide followed by reduction with ascorbic acid in the presence of ether. 

A proposed reference method for iron in serum that is a modification of the ICSH method was recently presented [51,52a]. The modifications include reduction with ascorbic acid and somewhat different concentrations of TCA and HCl. In addition, thiourea and ferrozine chromogenic chelators were used in the modified procedure. Thiourea reduces interference from copper [45b 52b,c]. Analysis was performed in a centrifugal analyzer. This procedure produced results that correlated very well with the Kodak dry-film procedure [48,49]. 

FIGURE 16.8 SEM images of electrospun (a) PI-3-23 wt%/AuNP 3 wt% thermal treatment at 200°C for 6 h and (b) chemical reduction with ascorbic acid. 

The phosphorus content offers a sensitive detection mode for fensulfothion, metasystox, disul-foton, methylparathion, folithion, hinosan, malathion, dimethoate, formothion, phosphamidon, phosalone, thiometon, and quinalphos. After development, the plates were heated at 110 C for 2 h, yielding inorganic phosphates. These reacted with anunonium molybdate to give phosphomolybdate. The reduction with ascorbic acid leads to a blue complex with a detection limit of 0.1-0.2 ftg (160). 

In an acidic medium, orthophosphates form a yellow-coloured complex with molybdate ions. The combination of P, Sb and Mo leads after reduction with ascorbic acid to the formation of a very stable blue-coloured phosphormolybdenum complex. At a wavelength of 880 nm a very sensitive and stable measurement of P... 

Catechol was purified by sublimation L-dopa and tiron were used as received. Structural formulae for the forms of these three substrates which predominate under the chosen experimental conditions are shown in Figure 3. Horse-heart cytochrome-c (Type VI) was purchased from the Sigma Chemical Co. in its oxidised form and was dialysed anaerobicaly at S C for 24 h following reduction with ascorbic acid. Final concentrations were determined from spectroscopic absorption ratios at 550 and 565 nm. Commercial samples of poly(4-vinylpyridine), (PVP, molecular masses 750,000 g and... 

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