Sodium metatungstate explained

Sodium metatungstate is the inorganic compound with the formula Na₆[H₂W₁₂O₄₀], sometimes written 3Na₂WO₄·9WO₃·H₂O. It is also referred to as sodium polytungstate (SPT). This salt has been used in the manufacture of dense aqueous solutions. Sodium metatungstate exists as white solid. The anion is the polyoxotungstate [H₂W₁₂O₄₀<nowiki>]^6-]], which features six-coordinated tungsten(VI) centers interconnected with doubly- and triply bridging oxo ligands.

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

Further reading

• 10.1080/00288306.1987.10552626 . A nontoxic substitute for hazardous heavy liquids—aqueous sodium polytungstate (3Na2WO4.9WO3.H2O) solution (Note) . 1987 . Gregory . Murray R. . Johnston . Keith A. . New Zealand Journal of Geology and Geophysics . 30 . 3 . 317. 1987NZJGG..30..317G .
• 10.2216/i0031-8884-36-6-472.1 . The use of sodium polytungstate for the separation and concentration of living dinoflagellate cysts from marine sediments . 1997 . Bolch . C. J. S. . Phycologia . 36 . 6 . 472–478. 1997Phyco..36..472B .
• 10.1016/S0038-0717(99)00023-1 . Recycling of sodium polytungstate used in soil organic matter studies . 1999 . Six . J . Soil Biology and Biochemistry . 31 . 8 . 1193–1196.
• 10.1144/jm.7.1.39 . The use of sodium polytungstate for conodont separations . 1988 . Savage . N. M. . Journal of Micropalaeontology . 7 . 1 . 39–40 . 1988JMicP...7...39S . 129701930 . free .

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Notes and References

1. 10.1016/0034-6667(95)00093-3 . Sodium polytungstate, a new non-toxic alternative to bromoform in heavy liquid separation . 1996 . Munsterman . Dirk . Kerstholt . Susan . Review of Palaeobotany and Palynology . 91 . 1–4 . 417–422. 1996RPaPa..91..417M .