Detector Systems
Electron capture detector (ECD)
139
Chemical Type
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 10
4
Mono-I, di-Br and nitro compounds 10
5
Di-I, tri-Br, poly-Cl and poly-F compounds 10
6
Relative Sensitivity
Table 7-2. General ECD Sensitivity to Various Classes of Compounds
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.
