Journal of Chromatographic Science, Vol. 30, December 1992 Environmental Applications of the Pulsed-Discharge Electron-Capture Detector W.E. Wentworth, Ela Desai D'Sa, and Huamin Cai Chemistry Department, University of Houston, Houston, Texas Stanley Stearns Valco Instruments Co, Inc., Houston, Texas Abstract A new type of electron-capture detector is introduced that does not require a radioactive source for the generation of electrons. Because a pulsed, high-voltage discharge is used instead, we have named this detector the pulsed-discharge electron-capture detector (PDECD). Preliminary results are given that demonstrate its viability as a detector for monitoring electron-capturing species in the environment. Especially impressive are the results obtained in the detection of chlorofluorocarbons (CFCs), which play an important role in the destruction of the ozone layer. Initial data obtained at a detector temperature of 100°C (with N 2 as dopant) for CHCI 3 , CCI 4 , CCI 2 =CCI 2 , CH 2 CI 2 , CFCI3, and CF 2 CI 2 resulted in minimum detectable quantities of 110 fg, 8 fg, 32 fg, 59 pg, 2 fg, and 83 fg, respectively. Similar MDQ values have been obtained using 0.2% H 2 as dopant. Electron-capture coefficients for these compounds are comparable with previous literature data from a radioactive ECD. Eight pesticides have been analyzed using the PDECD, and the resulting chromatogram gives symmetrical peaks. The minimum detectability for lindane was 250fg. The analytical importance of this detector is significant, and future work is being directed toward the use of this detector for field studies. Introduction Among the wide variety of gas-chromatographic (GC) detectors  currently marketed, the electron-capture detector (ECD) is gener- ally recognized as the most sensitive for the measurement of trace  levels of electron-capturing compounds, such as chlorofluorocar- bons (CFCs). The ECD was introduced in 1958 by Lovelock (1).  In his initial work, a constant potential was applied and the elec- tron attachment occurred with higher-energy electrons. Later, a  pulsed mode of operation was introduced (2), whereby the electron  attachment involved electrons with a thermal energy distribution.  Since that time, commercial detectors have used a radioactive  foil to generate electrons within the cell. In a conventional ECD,  a cavity is lined with a radioactive ionizing source made of Ni 63  or Sc 3 H 3 . A carrier gas (nitrogen, or Ar plus 5-10% CH 4 ) flows  through this cavity and is ionized by the radioactive source, pro- ducing positive ions and free electrons. These free electrons are  collected by applying a potential difference across two electrodes  in the cavity, and constitute what is called the standing current of  an ECD.  Use of the radioactive foil in the ECD has some disadvan- tages, however. The range of ß-particles emitted by Ni 63  is long  enough that it is difficult to use it in the construction of the low- volume detectors necessary for direct measurement from capillary  columns. Makeup gas can be used to lower the residence time in  a large-volume detector, but the addition of the makeup gas  lowers the sensitivity of this concentration-dependent detector.  Another disadvantage is the tendency of the foil to become con- taminated by analyte adsorption and subsequent analyte decom- position to nonvolatile products. The well-known catalytic effect  of Ni surfaces accelerates this process, especially at detector op- erating temperatures of 300-400°C (The temperature of the foil  is limited to 325°C for Sc 3 H 3  and 400°C for Ni 63 ). A higher tem- perature or a more sensitive detector would lower the detection  limit of compounds that capture electrons dissociatively and have  a low capture coefficient. Typically, the capture coefficient of  these compounds increases rapidly as the temperature increases.  Safety factors and the expense of handling radioactive material  are also concerns. The licensing of, monitoring the escape of, and  proper disposal of the radioactive material all add to the cost and  liability of radioactive foils.  Nonradioactive ECDs have been in development since 1964  (3). They use a variety of methods for the formation of elec- trons, including: (a) an electrical discharge prior to mixing with  the GC eluents (3); (b) a hydrogen Lyman alpha emission pro- ducing ionization of a dopant gas in argon (4); (c) a thermionic  emitter as an electron source (5); (d) the ionization of a dopant gas  by a rare gas resonance lamp source with a MgF 2  window (6); (e)  ultraviolet irradiation of a metal surface by the photoelectric ef- fect (7); (f) a microwave-powered helium resonance lamp ion- izing an argon-methane mixture (8); and (g) the use of metastable  species produced in a microwave discharge (9,10).  This paper introduces a new, nonradioactive ECD with a  promising future for commercialization. The unit is based on the  idea that ionization can be carried out in doped helium gas using  a high-voltage discharge. Because in this design the ionization is  caused by a pulsed discharge generated between two electrodes,  we call the new detector a pulsed-discharge electron capture de- tector (PDECD).  478 Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission. 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