DETECTORS
Photo Ionization Detector - PID
Troubleshooting and Maintenance
Over time,duringnormaloperation,afilmofcontaminantswillcondenseon the
PIDlampwindow. Typically, thisfilmisaresultofstationaryphasecolumnbleed. To
minimizecontaminantcondensationandthuslampwindowcleaning,avoidheatingthe
columnanyhigher thanabsolutelynecessary. Contaminantcondensationcanblock
thephotons,reducinglampemissionsandsensitivity. Therefore,thePIDlampwindow
mustbecleanedwhenanappreciablechange insensitivityhasbeenobservedby the
operator. Because the responsechange resulting fromcleaning the lampwindow
usuallyrequiresdetectorrecalibration,frequentcleaning isnotrecommended.
1. Turn thePIDcurrentOFFwith theswitchon theGC’s frontcontrolpanel. Turn theGCOFFand let the
PIDdetectorassemblycoolenough to touch itwithoutgettingburned.
2. Disconnect thehigh-voltagebandfrom the lampanodebyremoving
theblackplastichood.
3. Grasp thespring-loaded retainerplatewith the fingersofonehand
andpushorpull it toward thePID lamp; itdoesn’t takemuch force to
movetheplateenoughforlampremoval. SlidethePIDlampupandout
of thePIDdetectorassembly.
4. Clean the lampwindowusingamildabrasivecleanser likeBonAmi
orComet. Wetyour finger, andmakeapastewithasmall amountof
cleanser. Scrub the lampwindowclean inacircularmotionwithyourfinger.
5. Rinse the lampwindowcleanwithwater. Dry the lampwithapaper towel.
6. Inspect theTeflon
TM
sealforcutsornicks. Adamagedsealwillnotaffect the
PID response, but itmayprovidea leak site thatwill reduce theamount of
sampledelivered toanysubsequentdetector.
7. With the lampremoved, thecollectorelectrode isvisiblewhere itprotrudes
into the cell. Check the collector electrode for anyvisible residues, films,
discolorations,etc. Ifpresent,theymayimpedetheflowofionsfromthesample
molecules to thecollectorelectrode. Toclean thecollectorelectrode,gentlyuse
asmallfile toremoveanyresiduesfrom its tip. Blow theresidue
off thecollectorelectrodeandsurroundingareas.
8. Open the spring-loaded retainer plateand replace thePID
lampsnugagainsttheseal. Thelampwindowhasaslightlylarger
diameter than theseal; try tocenter itagainst theseal. Replace
thehighvoltageband /blackplastic lamphood.
9. Recalibrate thePIDdetectorbeforereturning it toservice.
Cleaning thePIDLamp
ThePID lampwindow
Makesure the lampwindow iscentered
over theTeflonseal andsnugagainst it
Thecollectorelectrode
protrudes into thecell
Teflon
TM
seal
