Electron Capture Detector (ECD)


	Electron Capture Detector ( ECD )


	The ECD detector consists of a sealed stainless steel cylinder containing radioactive Nickel-63. The Nickel-63 emits beta particles ( electrons ) which collide with the carrier gas molecules, ionizing them in the process. This forms a stable cloud of free electrons in the ECD cell. When electro-negative compounds ( especially chlorinated, fluorinated or brominated molecules ) such as carbon tetrachloride, bromoform, PCBs and pesticides such as DDT enter the cell, they immediately combine with some of the free electrons, temporarily reducing the number remaining in the electron cloud. The detector electronics which maintain a constant current ( of about 1 nanoampere ) through the electron cloud, are forced to pulse at a faster rate to compensate for the decreased number of free electrons. The pulse rate is converted to an analog output which is connected to the data system. The SRI ECD detector can be operated with either Nitrogen or Argon/5%Methane ( P5 ) makeup gas, and Nitrogen, P5, or helium carrier as long as the helium flow is less than 10 ml/min. The ECD offers extreme sensitivity ( parts per trillion for SF6 ). Because it contains 5 millicuries of Nickel-63, the ECD is covered by a "General License" requiring a periodic "wipe test" and the filing of a form with your state's Department of Health. In most states no annual fee is required. The ECD may be thermostatted from ambient to 375ºC 8690-0020 ECD detector ( Nickel-63 ) $5,495.00


	ECD vs. DELCD Both the ECD and DELCD detectors are useful for halogenated analytes. The ECD detects fluorine while the DELCD does not. Both detectors detect chlorine and bromine. The DELCD is much more selective than the ECD, which detects electro-negative molecules like oxygen as well as halogens. The selectivity of the DELCD can be exploited to reduce the amount of sample preparation required. PCBs for example can be detected by the DELCD even in the presence of massive co-eluting hydrocarbons. On the other hand the DELCD is less sensitive than the ECD, so larger amounts must be extracted and injected on-column.