Seawater, metal ions

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

In seawater—dolime and hrine—dolime processes, calcined dolomite or dolime, CaO MgO, is used as a raw material (Table 9). Dolime typically contains 58% CaO, 41% MgO, and less than 1% combined Si02, P O, and CO2 where R is a trivalent metal ion, eg, Al " or Fe " ( 4). Roughly one-half of the magnesia is provided by the magnesium salts in the seawater or brine and the other half is from dolime (75). Plant size is thus reduced using dolime and production cost is probably lower. 

Legin AV, Vlasov YG, Rudnitskaya AM, Bychkov EA (1996) Cross-sensitivity of chalcogenide glass sensors in solutions of heavy metal ions. Sens Actuators B 34 456 61 De Marco R, Shackleton J (1999) Cahbration of the Hg chalcogenide glass membrane ion-selective electrode in seawater media. Talanta 49 385-391... 

Complexation of fluoride by metal ions in seawater has previously been overcome by the addition of TISAB solution. The reagent is presumed to release the bound fluoride by preferential complexation of the metal ions with EDTA type ligands present in the TISAB. Examination of the metal ions present in seawater [66,67] suggests that magnesium is the major species forming fluoride complexes. Theoretical calculations demonstrate that even this species is unlikely to interfere. 

Several ions (e.g., manganese, iron (II), iron (III), cobalt, nickel, copper, zinc, cadmium, lead, and uranyl) react with pyrocatechol violet, and to some extent are extracted together with aluminium. The interferences from these ions and other metal ions generally present in seawater could be eliminated by extraction with diethyldithiocarbamate as masking agent. With this agent most of the metal ions except aluminium were extracted into chloroform, and other metal ions did not react in the amounts commonly found in seawater. Levels of aluminium between 6 and 6.3 pg/1 were found in Pacific Ocean and Japan Sea samples by this method. 

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. 

Titanates and silico-titanates The oxide and hydroxide of titanium are effectively used in applications of removing metal ions from water. Early studies (since 1955) have shown that hydrous titanium oxide is the most appropriate material for extracting uranium from seawater, whereas titanates and hydrous titanium oxide are suitable for removing strontium. 

Many analytes listed in Table 1 have been measured spectrophotometri-cally in seawater for some time, including many metal ions and some gases, although spectrophotometry is the preferred method for only a minority. Some analytes, like alkanes, are spectrophotometrically silent, or do not form colored complexes with other reagents. Similarly, individual nuclides cannot be distinguished by classical spectrophotometry, and many of the other analytes, such as halogenated pesticides and metal alkyls, are more easily determined by other methods, such as gas chromatography with electron capture detection, or emission spectroscopy. Indeed, many of the analytes, such as zinc or copper, are present at trace levels and are not measurable by spectrophotometry. 

Spectroscopic analysis can also benefit from a preceding electrochemical preconcentration. In particular, such coupling has been widely used for minimizing matrix interferences in atomic absorption spectroscopy (AAS). For example, lead, nickel, and cobalt have been determined in seawater with no interferences from the high sodium chloride content [80]. By adjusting the deposition potential and the pH, it is possible to obtain information on the oxidation and com-plexation states of the metal ions present [81]. 

Midorikawa, T., Tanoue, E. and Sugimura, Y. (1990) Determination of complexing ability of natural ligands in seawater for various metal ions using ion selective electrodes. Anal. Chem., 62, 1737-1746. 

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