Seawater, vanadium

Trace amounts of vanadium have been found in meteorites and seawater, and it has been identified in the spectmm of many stars including the earth s sun. The occurrence of vanadium in oak and beech trees and some forms of aquatic sea life indicates its biological importance. 

Vanadium is resistant to attack by hydrochloric or dilute sulfuric acid and to alkali solutions. It is also quite resistant to corrosion by seawater but is reactive toward nitric, hydrofluoric, or concentrated sulfuric acids. Galvanic corrosion tests mn in simulated seawater indicate that vanadium is anodic with respect to stainless steel and copper but cathodic to aluminum and magnesium. Vanadium exhibits corrosion resistance to Hquid metals, eg, bismuth and low oxygen sodium. 

Emerson SR, Huested SS (1991) Ocean anoxia and the concentrations of molybdenum and vanadium in seawater. Marine Chem 34 177-196... 

Shriadah et al. [516] determined molybdenum VI in seawater by densitometry after enrichment as the Tiron complex on a thin layer of anion exchange resin. There were no interferences from trace elements or major constituents of seawater, except for chromium and vanadium. These were reduced by the addition of ascorbic acid. The concentration of dissolved molybdenum (VI) determined in Japanese seawater was 11.5 pg/1, with a relative standard deviation of 1.1%. 

Kiriyama and Kuroda [597] combined ion exchange preconcentration with spectrophotometry using 2-pyridylazoresorcinol in the determination of vanadium in seawater. 

Van den Berg and Huang [600] carried out direct electrochemical stripping of dissolved vanadium in seawater using cathodic stripping. Voltammetry was performed with a hanging mercury drop electrode. The detection limit was 0.3 nmol/1 after a collection period of 2 min. 

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

Two methods for the determination of vanadium in seawater have been developed which use neutron activation analysis and atomic absorption spectrome-... 

Although the neutron activation analysis is inherently more sensitive than the atomic absorption spectrometry, both procedures yield a reliable measurement of vanadium in seawater at the natural levels of concentration. 

Huang and Shih [616] used a graphite furnace atomic absorption spectrometer with a stabilised platform furnace involving atomisation from a graphite surface pretreated with vanadium to determine down to 24 ppt of zinc in seawater. 

Tominaga et al. [682,683] studied the effect of ascorbic acid on the response of these metals in seawater obtained by graphite-furnace atomic absorption spectrometry from standpoint of variation of peak times and the sensitivity. Matrix interferences from seawater in the determination of lead, magnesium, vanadium, and molybdenum were suppressed by addition of 10% (w/v) ascorbic acid solution to the sample in the furnace. Matrix effects on the determination of cobalt and copper could not be removed in this way. These workers propose a direct method for the determination of lead, manganese, vanadium, and molybdenum in seawater. 

Chappie and Byrne [743] applied an electrothermal vaporisation inductively coupled plasma technique to the determination of copper, cobalt, manganese, nickel, and vanadium in seawater in amounts down to 3-140 ppt. 

Field et al. [747] used ICP high-resolution mass spectrometry to determine vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium, and lead in seawater. Each analysis required 50 p,l sample and a 6 minute analysis time. 

Alves et al. [744] determined vanadium, nickel, and arsenic in seawater in the 10-20 000 ppt range using flow injection cryogenic desolvation ICP-MS. 

Morris [814] separated microgram amounts of vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc from 800 ml of seawater by precipitation with ammonium tetramethylenedithiocarbamate, and extraction of the chelates at pH 2.5 with methylisobutyl ketone. Solvent was removed from the extract, the residue was dissolved in 25% nitric acid, and the inorganic residue was dispersed in powdered cellulose. The mixture was pressed into a pellet for X-ray fluorescence measurements. The detection limit was 0.14 pig or better when a 10 min counting period was used. 

Murthy and Ryan [823] used colloid flotation as a means of preconcentration prior to neutron activation analysis for arsenic, molybdenum, uranium, and vanadium. Hydrous iron (III) oxide is floated in the presence of sodium decyl sulfate with small nitrogen bubbles from 1 litre of seawater at pH 5.7. Recoveries of arsenic, molybdenum, and vanadium were better than 95%, whilst that of uranium was about 75%. 

In a method for the determination of copper, nickel, and vanadium in seawater, Shijo et al. [840] formed complexes with 2-(5-bromo-2 pyridylazo)-5-(N-propyl-N-sulfopropylamino) phenol and extracted these from the seawater with a xylene solution of capriquat. Following back-extraction into aqueous sodium perchlorate, the three metals were separated on a C is column by HPLC using a spectrophotometric detector. 

Tunicates (ascidians or sea-squirts) are invertebrate marine organisms, which can accumulate vanadium at concentrations approaching 350 mM (the concentration of vanadium in seawater is 10 8 M). This vanadium is taken up as V(V) from seawater (Figure 17.16), reduced to oxidation state III or IV and stored in a soluble form in the blood cells within acidic vacuoles at concentrations a million fold higher than in their external surroundings. 

A significant proportion of the needs for reference materials for seawater trace metal studies would be addressed by the preparation of these materials. Although the total iron concentration of these reference materials should be provided, these materials clearly will be useful for studies of other important metals such as zinc, manganese, copper, molybdenum, cobalt, vanadium, lead, aluminum, cadmium, and the rare earth elements. With careful planning, such water samples should be useful for analysis of dissolved organic substances as well. The collection sites should be chosen carefully to provide both a high and a low concentration reference material for as many metals as possible. 

Vanadium is an excellent alloy metal with iron that produces hard, strong, corrosion-resistant steel that resists most acids and alkali. It is even more resistant to seawater corrosion than is stainless steel. Vanadium is difficult to prepare in a pure form in large amounts. Impure forms seem to work as well as a very pure form of the metal when used as an alloy. When worked as a metal, it must be heated in an inert atmosphere because it will readily oxidize. 

The ascidians or tunicates (sea squirts) accumulate vanadium from seawater (about 5x 10-8 mol dm-3) to a level of about 1 mol dm-3 and store it in a dilute solution of sulfuric acid (pH<2) in blood cells called vanadocytes. The tunicates thus concentrate vanadium several million-fold. 079 NMR, ESR and EXAFS determinations on whole vanadocyte cells of Ascidia ceratodes and Ascidia nigra indicate that the vanadium is present mainly as aquated V111 probably complexed with sulfate. Some vanadyl ion (5-10%) is also present.1080 1081... 

Ion exchange separations may also be done in preparation for electrothermal atomisation. An interesting variant on this method is where the resin itself, containing the bonded analyte element, is subjected to direct analysis in the solid phase. In one example one litre of seawater is passed through 500 mg of chitosan (a natural chelating polymer). The resin was then homogenized and 5 mg samples of this were analysed for vanadium. Response of vanadium from the resin and from aqueous standards was shown to be the same. 

---