Sodium polytungstate

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Sodium polytungstate (SPT) is a compound which has been successfully used in the manufacture of heavy liquids for a relatively short period.

Solid SPT are white crystals and liquid SPT (solved in H2O) is a light yellow-green transparent solution. In a form of powder SPT is a 12-fold aggregated isopolytungstate with a molar mass of 2986.12 g/Mol. The structure of polytungstate is modelled using octahedrons in which the oxygen ions are located in the corners and the tungsten ions in the middle of the octahedrons. When represented as a spherical model, the oxygen ions form a dense spherical shell while the tungstate ions fill the open spaces in the octahedra. Because of this structure this substance may be considered a “true” metatungstate, represented structurally as Na6[H2W12O40]. It is known that in “true” metatungstates both of the protons are located in the central empty space of the polyanion and that they are unable to penetrate the external shell of the spherical casing.

The correct formula is Na6[H2W12O40] or 3Na2WO4·9WO3·H2O.

Due to its very high solubility in water (max. density 3.1 g/cm3) it is widely used as a heavy liquid for gravity separation (sink swim analysis) and density gradient centrifugation. It has significant advantages when compared to the use of the acid zinc chloride solution or the highly toxic halogenated carbons for sink swim analysis. SPT is non-toxic, non-flammable, odorless, reusable and additionally it has a low viscosity.[1]

References

  1. ↑ Munsterman, Dirk; Kerstholt, Susan (1996). "Sodium polytungstate, a new non-toxic alternative to bromoform in heavy liquid separation". Review of Palaeobotany and Palynology 91: 417. doi:10.1016/0034-6667(95)00093-3. 

Further readings

  • Gregory, Murray R.; Johnston, Keith A. (1987). "A nontoxic substitute for hazardous heavy liquids—aqueous sodium polytungstate (3Na2WO4.9WO3.H2O) solution (Note)". New Zealand Journal of Geology and Geophysics 30 (3): 317. doi:10.1080/00288306.1987.10552626. 
  • Bolch, C. J. S. (1997). "The use of sodium polytungstate for the separation and concentration of living dinoflagellate cysts from marine sediments". Phycologia 36 (6): 472. doi:10.2216/i0031-8884-36-6-472.1. 
  • Six, J (1999). "Recycling of sodium polytungstate used in soil organic matter studies". Soil Biology and Biochemistry 31 (8): 1193. doi:10.1016/S0038-0717(99)00023-1. 
  • Savage, N. M. (1988). "The use of sodium polytungstate for conodont separations". Journal of Micropalaeontology 7: 39. doi:10.1144/jm.7.1.39. 


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