In its crystal form, ruthenium (VIII) oxide (RuO4), is a golden yellow, volatile solid which sublimes at room temperature. It has a melting point of 25.4°C and a boiling point of 40°C. It is sparingly soluble in water (2% w/v at 20°C), but freely soluble in carbon tetrachloride. Solvents such as ether, alcohol, benzene and pyridine react violently with RuO4. Ruthenium tetroxide is not only less volatile and less toxic than osmium tetroxide but it is also a stronger oxidizing agent. It reacts with many organic compounds like olefins, sulfides, primary and secondary alcohols, and aldehydes. It also degrades benzene rings.
Ruthenium tetroxide is closely related to osmium tetroxide and it is useful as a staining agent for electron microscopy of polymers and their blends, and as a fixative for biological samples. It fixes the membranes in rat kidneys, liver, and ventral lobe of prostrate, and these membranes appeared thicker than those preserved with other fixatives. Ruthenium tetroxide shows excellent staining of saturated and unsaturated polymer materials with improved image contrast. RuO4 staining also has a stabilizing effect against electron beam damage of material films. Ruthenium tetroxide penetrates tissue very slowly, reacting strongly with proteins, glycogen, and monosaccharides.
A typical procedure consists of prefixing with buffered 4% glutaraldehyde, followed by post fixation with buffered ruthenium tetroxide 0.1-0.5% at a pH=7.1 for 1 hour at 40°C. Specimens should be rinsed in water before dehydrating with alcohol or acetone.
Ruthenium tetroxide is a strong oxidizing agent and must be stored in the refrigerator away from direct sunlight. It reacts violently with filter paper and alcohol. Do not place ruthenium tetroxide solutions into waste containers containing alcohol, ether benzene, pyridine, or other organic compounds.
Ruthenium tetroxide has an acrid odor. The vapors are irritating to eyes and the respiratory tract. Wear protective goggles and gloves and handle only in a fume hood. In case of spillage, flush with sodium bisulfite solution to decompose RuO4 and then flush with plenty of water.