Everything you want to know about sodium polytungstate

Solid sodium polytungstate contains at least 86% ± 1 % WO₃.
Bound water in the sodium polytungstate may vary very slightly.
Typical analysis results (no guaranteed values):

• Al ≤ 0,0015 %
• As ≤ 0,015 %
• Cu ≤ 0,001 %
• Fe ≤ 0,005 %
• Si ≤ 0,006 %
• Ti ≤ 0,001 %

The benefits of this heavy liquid solution are clear to see when sodium polytungstate SPT or LVP is compared with organic heavy liquids and aqueous LST:

In order to produce a heavy liquid solution, the SPT (SPT-0, -1, -2) must be dissolved in de-ionised water (ultrasound bath optional). The higher the concentration, the higher the density (checked e.g. with a hydrometer). The maximum achievable density of an aqueous solution is 3.1 g/cm³ at room temperature. The density can be lowered by adding water, or increased by evaporating the solution in a beaker (preferably with a large surface) at 70°C in a drying chamber. The liquid must not be boiled! You can also add solid SPT to increase the density again.

Producing the solution in this way allows fine granules, particles or solids to be separated by density (sink-float process). A laboratory centrifuge accelerates the separation process.

You can reduce the density of an SPT solution as required by adding de-ionised water.
This reduces the density as follows:

Initial solution: 500 ml solution SPT-3 with density of 3.00 g/cm³

Please notice that this table or better each cell is only valid for initial solution of 500 ml with density 3.0 g/cm³ because of an exponential dependence.

Also have a look at our SPT-Calculator (see calculator symbol right).

If you have reduced the density of the solution too much, you can increase it again by evaporating the solution in a beaker at 70°C in a drying chamber. Should the solution be brought to boiling note the following point.

Yes, a diluted SPT solution can be brought to boiling to drive out excess water and thus increase the density. The boiling point of SPT solutions is, as water, about 100°C. However, it is important to note that crystallization should be avoided when concentrating (initial skin formation on the boiling surface). This leads to a slight turbidity of the solution, which has no influence on the quality of the solution (except the optical properties). To avoid this we recommend not to exceed 70°C. At this temperature a SPT solution can also be completely and reversibly converted to a solid.
In general we recommend the use of a rotary evaporator at moderate temperatures.

Viscosity is shown in the following table and diagram as a function of density at 25°C. As seen in the figure, the viscosity only increases very slightly to a density of 2.5 g/cm³. This also allows separation within the fine grain range. The use of laboratory centrifuges can also accelerate the separation process here. If you need a very low viscosity please ask for LVP-3.

The pH value of the solution depends on the density. A solution with a density of 3.0 g/cm³ typically has a pH between 2 and 3. The solution has long-term stability at this pH value (several years). Each SPT solution must therefore be stored at a pH between 2 and 3.

The pH value can short term (several hours) be changed e.g. to a pH of 7 by adding e.g. NaOH. After completion of the test at the increased pH value, the solution should generally be reduced again to a pH of 2 to 3 using e.g. a few drops of HCl. Please recheck next day.

Like all electrolyte solutions, an aqueous solution of sodium polytungstate is also conductive. There is a maximum at a density of approx. 2.2 g/cm³ with a conductivity of 84 mS/cm. The conductivity decreases at lower densities and at higher densities.

It is a 12-fold aggregated isopolytungstate with a molar mass of 2986.12 g/Mol.

According to the models, polytungstate has a octahedral structure, in which oxygen ions are found in the corners and tungsten ions in the centre of the octahedra. As the spherical model shows, the oxygen ions form a very dense spherical shell, in which the tungsten ions are found in the open spaces of the octahedra.

The structure indicates that this compound is a “true” metatungstate with the formula

Na₆[H₂W₁₂O₄₀]

In a true metatungstate, the two hydrogen atoms are present in the central cavity of the polyanion, and cannot penetrate the spherical shell.

Our product SPT-3R is a recycled sodium polytungstate solution that we have reprocessed in a complex cleaning process. Ideally, customers collect their used SPT solutions and return them to us free of charge. We produce reusable solutions using multi-stage purification steps and offer these solutions at a lower price. SPT-3R solutions are ideally suited for simple sink-float analyses or for preparing suspensions and do not differ physically from original solutions, e.g. SPT-3. You can work with the recycled version as usual. As we depend on the return of used SPT solutions, availability is always limited. We also recommend not to dry SPT-3R solutions until they are solid. Likewise, SPT-3R is not suitable for elemental analyses or e.g. radiocarbon dating.