How to Determine Boiling Points on the Microscale

Chemtips

How do you tell when a liquid boils, if you only have 10 μL?

This isn’t a subject I think about often, largely because I assumed the analysis would require complex equipment and most of an afternoon. Flipping through “Microscale Techniques for the Organic Laboratory” last week [1], I found an elegant work-around. All that’s needed is a standard melting point apparatus, a melting point tube, and a small bit of glass.  The limit of detection seems to be around 5 μL, though I tested the setup at about twice that.

The trick is to drop a tiny, inverted tube into the melting point tube, before adding the liquid of interest. The trapped pocket of air acts as a micro boiling stone, and as the liquid boils a steady stream of bubbles is evolved. The boiling point is thus the temperature at which sustained bubble…

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