Sodium tungstate

Assay: 99.0 - 101.0%
Specifications:

Insoluble Matters: 0.01%
Chloride: 0.005%
Molybdenum: 0.001%
Nitrogen: 0.001%
Sulphate: 0.01%
Arsenic: 0.0005%
Heavy metals: 0.001%

Store at room temperature

Safety Data Sheet 

Stocker, J. C., Sodium Tungstate as a stain in Electron Microscopy. Bio.Cell. 29,211 (1977)