DETECTORS
Electron Capture Detector - ECD
General Operating Procedure
Thefollowingsuggestionsarespecific toyourSRIECD-equippedGC. Consult theValcoECDdetector
manualforcarriergaspurityrequirements,carriergassystemconfiguration,andothergeneralECDdetector
information. Keep inmind that theelectronicsshematics in theValcomanualdonotapply toyourECD-
equippedSRIGC.
1. Capoff thecarrier inlet to theECDcell (in thecolumnoven).
2. Connect themakeupgasand let it flow throughandpurge theECDcell.
Makeupflow is40-100mL; typically60mL.
3. Heat theECDdetector to150
o
C toverify that thebaselinenoiseandoffset
arenormal. 150
o
C ishotenough toevaporateoffwaterbut lowenough toavoid
oxidationof thenickelfoilwhichcanoccurathigh temperatures in thepresence
ofoxygen. OnceyouhaveverifiedtheECD’soperationatthistemperature,you
mayheat it tohigher temperatures.
4. Turnon theECD standingcurrent (theECDcurrentON /OFF switch is
located on the front control panel of the GC, under “DETECTOR
PARAMETERS”). Asaruleofthumb,anECDdetectorrequiresenoughnitrogen
makeupflow(40-100mL/min) tosignificantlydilute thecarrier inorder tohelp
keepdetectornoisedown;theECDcantoleratea6:1ratioofnitrogentohelium.
With thecarrierandmakeupgasconnectedandflowing,check the
offsetfromzero. Themillivoltreadingshouldbebetween100and
500mV. If thesignaloffset is less than100mV, thestandingcurrent
needs tobe increased. If thesignaloffset ishigher than500mV, the
standingcurrentneedstobedecreased. Oncethesignalisrelatively
quietandstable,set the temperature towhatever isappropriatefor
youranalysisbyadjusting the trimpot setpointwith the flatblade
screwdriverprovided.
5. When theECDdetectorcellreaches temperature, let thesystem
standuntilyougetastablemilliVoltreading. Oncethesystemexhibits
astablebaseline, reconnect thecolumn. Observe thesignal in the
presenceof thecarrierflow. If it issignificantlyhigher, it indicates
contamination introducedon thecarrierflow. If themilliVoltreading isstillrelativelystable in thepresenceof
carrier flow, then samplemaybe injected. Avoid sampleswithhigh concentrations of electronegative
compounds; theymayeffectECDoperationforsome time thereafter,as theycould take too long todissipate.
6. Youmayneed toadjust theECDstandingcurrentusing its trimpot setpoint. The trimpot setpointsare
locatedon the topedgeof thefrontcontrolpanel,directlyabove thedisplaypush-buttonsforeachcontrolled
zone. Remember, increasingthestandingcurrentincreasestheECD’ssensitivityandraisesthebaselineoffset.
ECDstandingcurrent
ON/OFFswitch
ECDcell temperaturedisplay
