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Osmium tetroxide

Sealed ampule.

Osmium(VIII)-oxide, ‘Osmic acid’
Linear Formula:
CAS Number:
Molecular Weight:
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Quality Level

vapor density

8.8 (vs air)

vapor pressure

7 mmHg ( 20 °C)



reaction suitability

reagent type: oxidant


130 °C (lit.)


39.5-41 °C (lit.)

SMILES string




InChI key


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General description

Osmium tetroxide (OsO4) is a heavy tetrahedral, symmetrical molecule composed of osmium, a third-row transition metal. Osmium tetroxide is both a dye, and a non-coagulant fixative agent in electron microscopy primarily used for the examination of biological tissue components in the histopathology laboratory. Specimens are postfixed with osmium testroxide to ensure preservation of the lipids.


Osmium tetroxide has been used as a fixative reagent for Brevibacterium mcbrellneri, and curcumin treated human lung cancer cell lines′ observation with a scanning electron microscope. It is also suitable as a fixative for ultrastructural analysis of Toxoplasma gondii′s skeletal muscle cells.


250 mg in ampule
1 g in ampule

Biochem/physiol Actions

Osmium tetroxide chemically combines with lipids making them insoluble; only 7% of the lipids can be extracted after the fixation. Therefore, the cell membranes comprising phospholipids become black and electron-dense after fixation in osmium tetroxide. It is also used to fix small amount of fat maintained in sections during paraffin processing.

Other Notes

Due to the hazardous nature of osmium tetroxide, it is recommended to use an ampule opener when using this chemical.


CorrosionSkull and crossbones

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Hazard Statements

Hazard Classifications

Acute Tox. 1 Dermal - Acute Tox. 2 Inhalation - Acute Tox. 2 Oral - Eye Dam. 1 - Skin Corr. 1B

Storage Class Code

6.1A - Combustible, acute toxic Cat. 1 and 2 / very toxic hazardous materials



Personal Protective Equipment

dust mask type N95 (US), Eyeshields, Gloves

Certificate of Analysis

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Certificate of Origin

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