70% Ethanol Preservatives

One of the commonest fluids recommended for long term storage is 70% ethanol, although it makes little difference whether it is made from pure ethanol or methylated spirits. Tissues can remain in this fluid for very long times. The fluid should be changed from time to time. Ethanol is a solvent and will extract some materials from the tissue, including some lipids. Using 70% concentration rather than 95% or absolute ethanol minimizes this. Storage in ethanol initially restores the colour of formalin fixed tissues, but this is temporary and the colour eventually fades again. It may not then be restored a second time.

A quick means of making a known concentration of ethanol from a stronger concentration without having to do any calculations is to take the volume equivalent to the concentration wanted and add water to the volume equivalent to the stronger concentration used. For example, to make 70% ethanol from 95% ethanol, take 70 mL of 95% ethanol and add enough water to bring the volume to 95 mL. You will then have 95 mL of 70% ethanol. This works for any dilution and all that is required is a large enough graduated cylinder.



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