Detector Systems

Electron capture detector (ECD)

Table 7-2. General ECD Sensitivity to Various Classes of Compounds

Chemical Type

Relative Sensitivity

 

 

Hydrocarbons

1

Ethers, esters

10

Aliphatic alcohols, ketones, amines;

100

mono-Cl, mono-F compounds

 

Mono-Br, di-Cl and di-F compounds

1000

Anhydrides and tri-Cl compounds

104

Mono-I, di-Br and nitro compounds

105

Di-I, tri-Br, poly-Cl and poly-F compounds

106

These are only approximate figures; sensitivity varies widely within each group, depending upon structure of the material. For example, DDT

(5 chlorine atoms/molecule) can be measured in the 1 to 10 picogram range.

The ECD is designed for use either with N or with 5% CH in Ar as carrier gas. A switch selects operation with either carrier gas; the ECD does not operate properly if the switch is incorrectly set. See Chapter 5 of the Operating Manual.

Because of its high sensitivity, the ECD should never be used without traps (moisture, chemical), should be in good condition, and should be installed in the carrier gas supply line. For capillary systems, this must also be done for the makeup gas supply.

An ECD is normally used to detect compounds that are reactive enough to interact with metal columns. Therefore, only 1/4•inchpacked glass, or fused silica, or glass capillary columns are recommended with this detector.

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