DETECTORS
Flame Photometric Detector - FPD
General Operating Procedure
1. Set thehydrogen flow to60mL/min. Thiscorrelates toa flowof30mL/mineach for theprimaryand
secondaryhydrogen. Set theairsupply to100mL/min. Theairsupply tubing isT’d inside theGCso that10-
30mL/minofairflowsacross thefaceof thePMT. Set thecarriergasflowbetween5and20mL/min.
2. Use theswitchon theGC’sfrontcontrolpanel to light theFPDflame. Sometimes theflame isdifficult to
lightbecauseof thehydrogen-richatmosphere inside theFPDdetectorbody. Ifyouarehavingdifficulty
lighting it,makesure thePMTvoltage isOFF, thenremove thecapon theFPDexhaustportand try the ignitor
switchagain. When theflame lights, therewillbea loudnoise like thebackfiringofacar; this isnormaland
doesnot indicateaproblem. KEEPYOURFACEAWAYFROMTHEDETECTORWHILELIGHTING
THEFLAME;theloudnoiseisaccompaniedbyaflashofflame. Replacetheexhaustcapnutafterlightingthe
flame.
3. Switchon thePMTvoltageandset it to400byusing theprovided flatbladescrewdriver toadjust the
trimpot setpointon the topedgeof theGC’s frontcontrolpanel (vertically labeled“PMTVOLTS”under
“DETECTORPARAMETERS”).
4. Set theFPD temperature to150
o
Cbyadjusting theappropriate trimpot setpoint. Set theFPDgain to
HIGH. Allow theFPDsignal tostabilize, then inject thesample.
OptimizingSensitivity
TooptimizeyourFPDdetector’ssensitivity, inject thesamesampleatvaryingairandhydrogenpressures
andobservethefluctuationsinsensitivity.
1. Inject sampleandobserve theFPD response.
2. Turn theairupa tinybit, less than1psi, injectsampleandobserve theFPDresponseagain. Ifyouseean
improvementinsensitivity,adjusttheairupalittlemore,injectagainandobservetheresponse. Keepadjusting
theairpressureupuntilsensitivitydropsagaintofindthewindowofoptimumsensitivity.
3. If there isno improvement insensitivityafter turning theairup, turn theairdown less than1psi, inject
sampleandobserve theFPDresponse. Ifyouseean improvement insensitivity,adjust theairdowna little
more, injectagainandobservetheresponse. Keepadjustingtheairpressuredownuntilsensitivitydropsagain
tofindthewindowofoptimumsensitivity.
4. Now, turn thehydrogenpressureup1-2psi and re-optimize theair. Repeat thisuntilyou’ve found the
optimumairandhydrogenpressuresettings.
Note:
Whena largehydrocarbonpeakelutessimultaneouslywitha targetsulfurcompound, thehydrocarbon
peakwillquench thesulfur response. For this reason,SRI recommends theadditionofanFIDcollector
electrodetotheFPDdetectorbody. TheFIDcollectorelectrodewillallowtheoperatorto“see”thehydrocarbon
peaksand theirretention times,so thatchromatographicseparationcanbeoptimizedfor theelutionofsulfur
compounds.
