ECD - Electron Capture Detector
5Pages

DETECTORS Electron Capture Detector - ECD OVERVIEW The Electron Capture Detector (ECD) is selective to electronegative compounds, especially chlorinated, fluorinated, or brominated molecules. It is sensitive to some of these compounds in the parts per trillion (ppt) range. The ECD detector requires nitrogen or argon / 5% methane (P5) to operate. The ECD detector is mounted immediately adjacent to the right rear column oven wall on your SRI GC chassis. Two BNC cables connect the anode and cathode, respectively, to the ECD amplifier. The ECD detector consists of a stainless steel cylinder containing 5 millicuries of radioactive Nickel 63 in an oven enclosure that is thermostatically controllable from ambient temperature to 375oC. Since the detector contains only 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. The documentation necessary to authorize your possession of a radioactvie source is included in the ECD manual from Valco, the manufacturers. This documentation transfers possession of the ECD directly to you from Valco; SRI provides the ECD installation service and the GC. There are four important documents to look for: 1) Certification of Sealed Source, 2) Conditions for Acceptance of a Generally Licensed Device, 3) Test Specifications, and 4) Record of Source Transfer. Valco may print your address on the multiple copies of the Record of Source Transfer, which are to be completed by you and filed with the appropriate state and local authorities. The other documents remain with the ECD detector, and Parts kit are necessary to prove authorized possession of the ECD. containing test resistor ECD Detector Trimpot setpoints 2 3 It is imperative to complete the Record of Source Transfer and forward it to proper authorities, and to familiarize yourself with the requirements of your General License. You must also keep on file the Cerification of Sealed Source and Test Specifications, which are proof that your ECD detector meets regulations. Close-up view of the ECD detector on an SRI GC Your name & address h

DETECTORS Electron Capture Detector - ECD Theory of Operation The radioactive Nickel 63 sealed inside the ECD detector emits electrons (beta particles) which collide with and ionize the make-up gas molecules (either nitrogen or P5). This reaction forms a stable cloud of free electrons in the ECD detector cell. The ECD electronics work to maintain a constant current equal to the standing current through the electron cloud by applying a periodic pulse to the anode and cathode. The standing current value is selected by the operator; the standing current value sets the pulse rate through the...

DETECTORS Electron Capture Detector - ECD Expected Performance ECD Noise Run Column: 15m MXT-5 capillary Carrier: Helium @ 10mL/min Makeup: Nitrogen @ 60mL/min ECD Temp: 250oC ECD standing current: 300 Offset before zeroing the data system signal: 280mV ECD noise averages less than 1mV from peak to peak Sample: 1µL 200ppb chlorinated pesticides Column: 15m MXT-5 capillary Carrier: Helium @ 10mL/min Makeup: Nitrogen @ 60mL/min ECD temp: 250oC ECD standing current: 300 Results: Component Pesticides

DETECTORS Electron Capture Detector - ECD General Operating Procedure The following suggestions are specific to your SRI ECD-equipped GC. Consult the Valco ECD detector manual for carrier gas purity requirements, carrier gas system configuration, and other general ECD detector information. Keep in mind that the electronics shematics in the Valco manual do not apply to your ECDequipped SRI GC. 1. Cap off the carrier inlet to the ECD cell (in the column oven). 2. Connect the makeup gas and let it flow through and purge the ECD cell. Makeup flow is 40-100mL; typically 60mL. 3. Heat the ECD...

DETECTORS Electron Capture Detector - ECD ECD Troubleshooting If you are experiencing baseline offset and noise problems withyour ECD detector, try the following two diagnostic tests: 1. Verify that the ECD amplifier electronics are working properly by removing the detector from the circuit and inserting a 1000MOhm test resistor in its place. The parts kit in the tackle box included with your GC under the red lid contains a 1000MOhm resistor for this test. Turn the ECD current off. The anode and cathode connections are BNC connectors located on the GC chassis near the base of the ECD...