DETECTORS
Flame Ionization Detector - FID
TheFlameIonizationDetectorrespondstoanymoleculewithacarbon-hydrogenbond,butitsresponse
iseitherpoorornonexistent tocompoundssuchasH
2
S,CCl
4
,orNH
3
. Since theFID ismasssensitive,not
concentrationsensitive,changesincarriergasflowratehavelittleeffectonthedetectorresponse. Itispreferred
forgeneralhydrocarbonanalysis,withadetectionrangefrom0.1ppm toalmost100%. TheFID’sresponse
isstable fromday today,and isnot susceptible tocontamination fromdirtysamplesorcolumnbleed. It is
generallyrobustandeasy tooperate,butbecause itusesahydrogendiffusionflame to ionizecompoundsfor
analysis, itdestroys thesample in theprocess.
Overview
TheSRIFID featuresauniqueceramic
ignitorwhichcanrunhotcontinuously,andprevent
theflamefromextinguishingevenwithlargewater
injections or pressure surges from column
backflush. Thisignitorispositionedperpendicular
to the stainless steel detector jet and does not
penetrate the flame. Opposite this flame is the
collectorelectrode. Thispositivelychargedmetal
tubeservesasacollectorfor the ionsreleasedas
eachsamplecomponentelutesfromthecolumn(s)
and ispyrolyzed in theflame; itdoublesasavent
for theFID exhaust gas. TheFID is equipped
withanelectrometeramplifierwhichhasHIGH,
HIGH(filtered),andMEDIUMgainsettings. On
anSRIGC, thehydrogenandairgas flowsare
controlledusingelectronicpressurecontrollers,
whichareuseradjustableviatheGC’sfrontpanel.
Athermostattedaluminumheaterblockmaintains
a stable detector temperature which is user
adjustableup to375
o
C. Theoptionalbuilt-inair
compressormaybeused tosupply theairfor the
FID,eliminatingbulkyaircylinders. Thebuilt-in
hydrogengeneratorisanotheroption:thestandard
model can produce 20mL/min for use as both
carriergasandFIDcombustiongasatpressures
up to25psi.
Collector
electrode
Ceramic
ignitor
H
2
in
Air in
FIDdetector
(SRICapillaryFIDGCwithbuilt-inHydrogenGenerator)
Detectorviewport
(removeSwagelokcap)
Thermostatted
heaterblock
Flameport
Amplifiergainswitch
Electrode lead
toamplifier
