Supplement to 'Making your own paraffin sections @ home (part 1)…' by Yvan Lindekens

 

That’s difficult to say. As everyone I followed the instructions from the textbooks: “replace your dehydration fluids after two or three samples”. But I also noticed that those few samples dehydrated in an already several times used dehydration series turned out okay. That kept me thinking on economizing on alcohol.

 

My girlfriend did some approximate calculations. She assumed that each jar in the dehydration series contains 99ml, 49ml or 24ml of dehydration fluid respectively and that 1ml of water per sample was brought in the first dehydration step (ethyl alcohol 70%).

I assumed equal concentrations in both the isopropyl alcohol and in the sample at the end point of each dehydration step. 

These calculations show that the final water content in the isopropyl alcohol III stays very low even after dehydration of lots of samples.

 

Given the fact that some water content in the dehydrated sample can be tolerated, it’s not at all necessary to refresh the alcohols that often. 

I consider a final water content in the specimen of less than 1% prior to infiltration with paraffin wax satisfactory.

Dieter Gerlach even suggests in “Botanische Mikrotechnik” that some samples benefit from only partial dehydration, up to ethyl alcohol 90%.

 

The graph shows the results of the calculations Annick made: even in the situation of 24ml alcohol + 1ml  of water from the sample (“24 + 1”), 24 samples can be dehydrated in the dehydration series before the last alcohol in the series drops below 99% alcohol concentration.

 

 

Of course, the water content of the final alcohol step isn’t the only consideration: samples brought in a (too) low alcohol concentration tend to macerate; thus giving poor sections/slides when these stay there too long. A considerable drop in alcohol concentration occurs especially in the first dehydration step (ethyl alcohol 70%). And there is also the contamination of the alcohols with rest products from the fixation, fats and oils from the sample, chlorophyll… to consider.

 

It seems safe to say that the final amount of water in the dehydrated sample should be less than 1% and the alcohol concentration of the dehydration fluids shouldn’t drop more than 10% below their original concentration at any stage of the dehydration process.

That gives the following results regarding the amount of samples to dehydrate per dehydration series:

 

Scenario	# samples
24 ETOH + 1 H2O	3
49 ETOH + 1 H2O	7
99 ETOH + 1 H2O	15

 

Given all the assumptions in the calculations a safety margin is appropriate.

 

% IPA after dehydratation of Sample, IPA III init.100 %