Electron Capture Detector (ECD) is a technique used to analyse halogenated compounds and is primarily found in the environmental, forensic and pharmaceutical markets. An ECD operates using two electrodes with a current passing between them. When a sample passes between these two electrodes, the molecules pick up some of the electrons, causing a reduction in the current. This reduction is recorded as a positive peak in the detection of components. An ECD is often used in conjunction with a GC instrument.
As common with other GC techniques a carrier gas is required with low water and oxygen impurities. These can interact with the stationary phase causing significant problems including high baseline noise and column bleed in the output gas chromatogram, resulting in reduced analyser sensitivity and decreased column lifespan. Oxygen and water impurities can also oxidise the radioactive nickel source used to generate the base current, additionally the carrier gas should have exceptionally low levels of halocarbons as the ECD is extremely sensitive to these compounds.
The GC-ECD also requires a make-up gas if helium is used as the carrier gas, since this make-up gas serves to provide the electrons that are not contained within the helium, as the base current. The routine calibration of the analyser using a calibration mixture is common.
Air Products' range of Experis® ultra-high-purity gases, unique BIP® technology and gas mixtures have been specifically designed to improve both the accuracy of analysis and increased lifespan of core GC-ECD components by minimising the critical impurities in the gases supplied.
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Which grade of helium or nitrogen should I use for ECD applications?