Gas Chromatography - GC Detectors > The Electron Capture Detector > Page 44

The basic electron capture detector consists of a small chamber one or two ml in volume enclosing two metal electrodes. The electrodes may be concentric cylinders or metal discs separated by an insulator. The cell contains the radioactive source, electrically connected to the entrance conduit and to the negative side of the power supply. A gauze "diffuser" is connected to the cell exit and to the positive side of the power supply. The output from the sensor is processed by suitable electronics and the output passed to either a potentiometric recorder of a computer data acquisition system. The electron capture detector is very sensitive, probably the most sensitive GC detector available (ca. 10-13 g/ml) and is widely used in the analysis of halogenated compounds, in particular, pesticides. An example of a pesticide analysis employing an electron capture detector is shown in figure 28.

1 a-BHC 2g-BHC (Lindane) 3 b-BHC 4 Heptachlor
5 d-BHC 6 Aldrin 7 Heptachlor Epox. 8 Endosulphan
9 p,p'-DDE 10 Dieldrin 11 Endrin 12 p,p'-DDD
13 Endosulphan 11 14 p,p'-DDt 15 Endin Aldehyde 16Endosulp. Sulf.


Courtesy of Supelco Inc.


Figure 28. The Analysis of Priority Pollutant Pesticides


The column used was a SPB-608 fused silica capillary column, 30 m x 0.53 mm I.D. with a 0.5 m film of stationary phase. The column was programmed from 50oC at 1o/min. to 150oC and then to 260oC at 8o/min. Helium was used as the carrier gas at a flow rate of 5 ml/min. The sample consisted of 0.6ml of a solution of the pollutants in n-decane. The mass of each pollutant present was about 120 pg.