Gases for Electron-Capture Detection

The answer to the following question was provided by LCGC’s “GC Connections” columnist John Hinshaw.

Q: What do you advise using as gases with electron-capture detection (ECD) for gas chromatography? Would it be better to purchase higher quality gases or to place an oxygen trap between the gas bottle and the detector? Which setup would be the most cost-effective?

John Hinshaw: The best choice is to use both high quality gases and an oxygen trap. A high-purity, high-quality gas cylinder will contain absolute minimum amounts of contaminants such as hydrocarbons, air, water, and other chemicals that could interfere with the electron-capture detector’s operation. After the high-purity gas leaves the cylinder, however, it can become contaminated with traces of oxygen and water if additional steps are not taken. A suitable high-purity pressure regulator with stainless steel diaphragm, clean chromatography-rated tubing, and leak-tight tube fittings will ensure the gas maintains its purity. A combination oxygen, water, and hydrocarbon filter, placed in-line as close as possible to the instrument, will remove the traces of oxygen or water that may enter the gas stream between the cylinder and the instrument, as well as trace amounts of hydrocarbon. And don't forget to make sure the internal connections that lead to the detector are leak-tight for the column as well as for makeup gas. This includes all column and inlet seals as well as carrier gas connections, including appropriate filters, all the way back to both the carrier gas and makeup gas cylinders.

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