Which Cold Trap is Best for my Samples?

By Jenny Sprung, Senior Application Specialist

On December 17, 2015 in Articles

Which Cold Trap is best for my Samples?

During evaporation, the main function of the Cold Trap is to collect vapors prior to entering the vacuum pump. For an oil-based vacuum pump, collection of the vapors is essential as it prevents oil vapors from getting into the vacuum pump and collecting in the oil.

If corrosive or water vapors collect in the oil, the vacuum pump will be damaged and eventually the vacuum pump will cease beyond repair.

For non-oil based vacuum pumps, collecting the vapors prior to the vacuum pump makes the evaporation system a closed system, preventing vapors from passing through the vacuum pump and into the environment.

In the evaporation process, the Cold Trap is the coldest spot in the evaporation system. Vapor molecules naturally migrate to the coldest spot, where they freeze and are trapped in the condenser. Because of this natural migration of the vapor molecules, Cold Traps can increase evaporation rates.

The evaporation rate is increased as vapor molecules are collected as a frozen solid and are not condensing inside the vacuum tubing, slowing down evaporation.

What is the best option for my sample?

A Cold Trap collects and freezes the vapors evaporating from a sample during the evaporation process. Cold Traps are offered in three temperature choices, -50°C, -85°C and -105°C.

Choosing the correct Cold Trap temperature will optimize the trapping efficiency. It is important to select a cold trap that reaches temperature that is colder than your sample’s freezing point. For example, with methylene chloride which has a freezing point of -96.7°C, a -50°C Cold Trap collected 43.3% of the methylene chloride, while a -105°C collected 87.7% of the initial starting volume.

For water samples, the -50°C will collect the same amount as the -105°C Cold Trap. If the sample is a mixture of solutions, the Cold Trap temperature should be matched to the component with the lowest freezing point.

Following this general guideline will ensure the best trapping efficiency thus preventing vapors from going into the pump and the environment.

Type of Sample: Suggested Cold Trap Temperature

• Aqueous: -50°C
• Solvents such as
  acetonitrile, chloroform: -85°C
• Alcohols such as
  ethanol, methanol: -105°C

Choosing the correct Cold Trap for your samples is essential for protecting your pump and protecting the environment.