Detector Systems
Electron capture detector (ECD)
Considerations for packed column operation
Either N or Ar containing 5 or 10% CH , may be used as carrier gas.
Nyields somewhat higher sensitivity, but it is accompanied by higher noise; minimum detectable limit is about the same. N sometimes produces a negative solvent peak. Ar/CH gives greater dynamic range.
The carrier gas must be dry and O •free.Moisture and O traps are strongly recommended for highest sensitivity. Because plastic tubing is permeable to many gases, use copper tubing for all connections.
Total flow into the detector must be at least 20 ml/min to prevent peak tailing.
Considerations for capillary column operation
H carrier gas (with N makeup gas) gives best column performance. Ar/CH as makeup gas may also be used. For most purposes, 60 ml/min of makeup gas is satisfactory. For very fast runs this can be increased to 100 ml/min to sharpen peaks, but some sensitivity will be lost since the ECD is a concentration•dependentdetector.
Hor He carrier gas affords the best column performance with reduced retention times. Ar/CH or N makeup gas is used in the range of
Moisture and O traps for carrier gas are essential with capillary/ECD operation.
Temperature
Some compounds exhibit strong dependence of response to detector temperature. The effect may be either positive or negative. Different detector temperatures may be tried, always remaining above the oven temperature, to determine the effect on sensitivity. Generally a detector temperature between
140