>Has anyone out there done this and if so have any tests been done to see if
>there is any isotopic effects on oxygen or carbon?

Hallo David!

I tested sodium politungstate for heavy mineral separation. It works fine,
better than bromoform
(you can prepare it at 2.95 density, bromoform has only 2.85). One day
after the preparation,
the solution is less viscous and it is easier to work with.

During the separation:
a) you can dilute the solution so that you can get progressively lighter
and lighter minerals on the
bottom of the separation flask.
b) it is recommended to stir (mechanically or manually but no metal) in the
upper part of the
separation flask.
The dilute sodium polytungstate solution can be enriched again by
evaporation on a hot plate.
Concentrates should be cleaned with lots of water.

Hope that helps,

Ana-Voica Bojar