Absorption vanadium

The rate and extent of vanadium absorption in humans is not known. 

Animal studies generally support the concept that vanadium is poorly absorbed (< 10%). A significant amount of vanadium absorption occurs in the upper gastrointestinal tract. Most ingested vanadium probably is transformed to VO in the stomach and passes into the duodenum in this form. In-vitro studies have suggested that vanadate can enter cells via the phosphate or other anion transport system, and this may be why V is absorbed three to five times more effectively than V. ... 

The apparent mean rate of vanadium absorption by adults of both diet forms amounts to 10%, and the mean vanadium balance is + 6% (range from + 23 to —15%). 

As the emission lines of hollow cathode lamps are very narrow, interference due to overlapping lines is rather unlikely. The separation between two spectral lines would have to be less than typically 0.01 nm for such an interference to occur. As an example, the vanadium absorption line at 308.211 nm interferes in the anal-... 

This is first heated to 50°C with a little sodium chlorate to oxidize the vanadium and is then used as the feed for vanadium absorption in a column of a strong base anion-exchange resin. The oxidation equation is ... 

Another example of this type of interference involves the enhancement of vanadium absorption when aluminum or titanium is present. 1 he interference is significantly more pronounced in fuel-rich flames than in lean flames. These effects can be explained by assuming that the three metals interact with such species as O and OH, which are always present in flames. If the oxygen-bearing species are given the general formula Ox, a series of equilibrium reactions can be postulated. Thus,... 

Vanadium Absorption Vanadate has been suggested to be absorbed through phosphate or other anion transport systems vanadyl has been suggested to use iron transport systems. Absorption occurs in the duodenum <10% Converted into vanadyl-transferrin and vanadyl-ferritin whether transferrin is the transport vehicle and ferritin is the storage vehicle for vanadium remains to be determined. Bone is a respository for excess vanadium... 

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

The above considerations will be illustrated by the simultaneous determination of manganese and chromium in steel and other ferro-alloys. The absorption spectra of 0.001 M permanganate and dichromate ions in 1M sulphuric acid, determined with a spectrophotometer and against 1M sulphuric acid in the reference cell, are shown in Fig. 17.20. For permanganate, the absorption maximum is at 545 nm, and a small correction must be applied for dichromate absorption. Similarly the peak dichromate absorption is at 440 nm, at which permanganate only absorbs weakly. Absorbances for these two ions, individually and in mixtures, obey Beer s Law provided the concentration of sulphuric acid is at least 0.5M. Iron(III), nickel, cobalt, and vanadium absorb at 425 nm and 545 nm, and should be absent or corrections must be made. 

The oil is dissolved in white spirit and the absorption to which this solution gives rise is compared with that produced from standards made up from vanadium naphthenate dissolved in white spirit. 

A double-beam atomic absorption spectrophotometer should be used. Set up a vanadium hollow cathode lamp selecting the resonance line of wavelength 318.5 nm, and adjust the gas controls to give a fuel-rich acetylene-nitrous oxide flame in accordance with the instruction manual. Aspirate successively into the flame the solvent blank, the standard solutions, and finally the test solution, in each case recording the absorbance reading. Plot the calibration curve and ascertain the vanadium content of the oil. 

The laser beam expander will also be used to minimize local heating which may result from absorption by either colored adsorbates (e.g. some carbonium ions) or colored adsorbents (e.g. some vanadium oxides). 

Fig. 3. Frequencies of three representative vanadium atom absorptions in different open-chain C Hj,+8 matrices (where n = 1-10), compared to gas-phase and argon-isolated atomic vanadium (109).

V0x/Zr02 catalysts were designated as ZVx(y)pHz, where x gives the analytical vanadium content (weight percent), y specifies the preparation method (a, adsorption, i, impregnation or acac, acetylacetonate) and z the AV solution pH. The V-content was determined by atomic absorption (Varian Spectra AA-30) after the sample had been dissolved in a concentrated (40%) HF solution. 

Position of the K-Absorption Limits of Vanadium in Its Compounds, Hendricks... 

Monien and Stangel [598] studied the performance of a number of alternative chelating agents for vanadium, and their effect on vanadium analysis, by atomic absorption spectrometry with volatilisation in a graphite furnace. Two promising compounds were evaluated in detail, namely 4-(2-pyridylazo) resorcinol in conjunction with tetraphenylarsonium chloride and tetramethylenedithiocar-bamate. These substances, dissolved in chloroform, were used for extraction... 

Vega and Van den Berg [601] determined vanadium in seawater in amounts down to 70 pM by absorptive stripping voltammetry. 

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