Uranyl formate (UO2(CHO2)2·H2O) is a salt that exists as a fine yellow free-flowing powder occasionally used in transmission electron microscopy. It is used as a negative stain in transmission electron microscopy (TEM) because it exhibits a finer grain structure than uranyl acetate. However, uranyl formate does not easily dissolve, and once in solution, it has a limited lifespan as a stain. Typical aqueous solution concentrations are 0.5% or 1%. It is highly sensitive to light, especially ultraviolet light, and will precipitate upon exposure.
See also Electron microscope
References 2SPI.com Archived 2015-07-03 at the Wayback Machine, compound information, retrieved May 3, 2011.