Karnovsky's Paraformaldehyd/Glutaraldehyde Fixative, different packing units

The KARNOVSKY fixative is often used in electron microscopy. The originally by Dr. M. Karnovsky developed mixture of 5% glutaraldehyde and 4% paraformaldehyde in 0.1 M cacodylate buffer was extremely hypertonic. It was later modified for lower aldehyde concentrations and even the use of phosphate buffer. In fact, the name “Karnovsky’s” is nowadays a general term for any fixative that contains both Glutaraldehyde and Paraformaldehyde in various concentrations in a buffer of your choice. The aldehydes in this fixative complement each other because compared to the individual compounds, the mixture leads to better tissue penetration. In combination, the cell ultrastructure is quickly stabilized with paraformaldehyde, as this small monocarbon aldehyde quickly penetrates tissue and denatures proteins by reacting with their alpha-amino group. Glutaraldehyde is a larger five-carbon dialdehyde that has a slower penetration rate (approximately 1 mm/h) but cross-links proteins with the two aldehyde groups, better stabilizing the structure and reducing possible extraction during subsequent processing steps. Stabilization of cellular proteins, rapid tissue penetration and optimal preservation are the greatest advantages of the Karnovsky solution.

Using Paraformaldehyde-Glutaraldehyde Solution (Karnovsky's Fixative)

Kit contains

• 2 x 10 ml 16% Paraformaldehyde Solution
• 1 x 10 ml 50% EM Grade Glutaraldehyde
• 1 x 50 ml Sodium Phosphate Buffer .2M, pH 7.2

Mixture 1 (Original Karnovsky's Mixture)

• 16% Paraformaldehyde Solution 20 ml
• 50% Glutaraldehyde EM Grade 8 ml
• 0.2M Sodium Phosphate Buffer 25 ml
• Distilled Water 25 ml

Final mixture is 78 ml with 5% Glutaraldehyde, 4% Formaldehyde in 0.064M buffer. This mixture is extremely hypertonic, with an osmolarity of more than 2000m OSM .

Mixture 2

A lower concentraction of Glutaraldehyde and Formaldehyde especially used for vascular profusion.

• 16% Paraformaldehyde Solution 13 ml
• 50% Glutaraldehyde EM Grade 5 ml
• 0.2M Sodium Phosphate Buffer 50 ml
• Distilled Water 32 ml

Final mixture is 2% Paraformaldehyde, 2.5% Glutaraldehyde and 0.1M Buffer. If necessary, the osmolarity can be adjusted by adding sucrose to NaCl. The pH may also need to be adjusted to your desirable point. This mixture is the most effective general fixative for both plant and animal specimens.