Woulff Bottles: What They Are and How They Are Useful in Rotary Evapor

By Aimee O'Driscoll, 17 April 2018

A Woulff (sometimes spelled Woulfe) bottle is a specialized vessel with two or three outlets and is designed for specific applications. These items have been around since at least the 18th century, when chemist Peter Woulfe described using a vessel with two outlets while conducting a series of experiments.

One popular use case for a Woulff bottle is as an intermediary flask for vacuum work to help collect solvents and/or control vacuum. They may also be used for washing gases or dissolving them in solvents. In a rotovap system, a Woulff bottle can be used to prevent solvents damaging the pump.

In this post, we explain in more detail what a Woulff bottle is and how it can be useful.

What Is a Woulff Bottle?

As mentioned, a Woulff bottle is often two-necked, but you might come across a three-necked version. Here are some examples of what they may look like:

Examples of Woulff bottles.

Left: A Woulff bottle for Heidolph Hei-VAP models. Right: An IKA Woulff bottle with a bracket.

A Woulff bottle can act as a condensate trap for gases and can therefore be used for collecting them, purifying them, or dissolving them in solvents.

How Is a Woulff Bottle Useful in a Rotovap System?

When used in a rotary evaporator setup, the Woulff bottle aids in additional recovery of the solvent. It is connected ahead of the vacuum pump and acts as a condensate trap. The Woulff bottle provides a larger surface area for cool, but not yet condensed, vapor to condense on.

Once it does condense, the now liquid particles are trapped and cannot run along the vacuum line to the pump. Getting solvent in the vacuum pump can damage it over time, or cause it to cease functioning should enough liquid become trapped inside it.

Using a Woulff bottle in this setup can help prolong the lifespan of the vacuum valve and pump. A more efficient option would be to use a cold trap but these are typically far more expensive. A Woulff bottle offers a practical and more economical solution.

The image below shows a rotary evaporator setup with a Woulff bottle included.

An RV 8 Rotary Evaporator.

An RV 8 Rotary Evaporator.

One more reason that a Woulff bottle is useful in a rotovap setup is that it can be connected directly to the vacuum valve and fitted with a vacuum controller. This is particularly helpful if the vacuum pump’s flow is too high for an application or you need more precise manual control over the vacuum to optimize evaporation rates.