General Operating Procedure
1. Set theHIDamplifiergain switch toHIGH formost applications from theppm level to1%. Use the
MEDIUMgainsettingforslightlymoreconcentratedsamples.
2. Settheheliummake-upgasflowto40mL/min,andtheheliumcarriergasflowto10mL/min. Themake-up
gasflow iscritical to theHID’sperformance. With insufficientmake-upflow, thechlorinatedpeakswillbe
invertedon thechromatogram;see thechromatogramscomparedon the
HIDMake-upGasFlow
page. Clean,
highpurityhelium isbest;moisture,air,andothercontaminantscancauseproblems.
3. Set theHID temperature to200
o
C. This temperaturewill helppreventmoistureaccumulation in the
detector’sarcassembly.
4. Zerothedatasystemsignal, thenswitchONtheHIDcurrent;theswitchislocatedontheGC’sfrontcontrol
panelunder“DETECTORPARAMETERS.” Set theHIDcurrentat100using the trimpotsetpointon the top
edgeof thefrontcontrolpanel.
5. When theHID isOFFand thesignalzeroed,and theHID is then turnedON, themilliVoltoffsetatHIGH
gainsettingshouldbe200-800mV. Ahigheroffsetmeansmoresensitivity,butlessdynamicrange. Iftheoffset
is less than200, thearcandgroundelectrodesareprobably tooclose.
6. Observe thearcwindow; ifyoucansee thepurplearcbetween thegroundandarcelectrodes,proceed to
step7. If thearcgoessideways to thedetectorbody insteadofdown to thegroundelectrode, then thegap
between theelectrodes is too large. Ifyoucannot see thearc,
A. Useamultimeter tocheck thevoltagebetween thearcandgroundelectrodes. With theHID
current at100, thevoltage readingshouldbegreater than200VDC (our readingsaveragearound
240VDC).
B. Look through thearcwindowat thearcandgroundelectrodes. If theyappear tobe touching,
disconnecttheredelectrodeleadwirethencheckthecontinuitybetweentheelectrodesusingamultimeter;
thereadingshouldbeopenor infinite.
C. If thecontinuitybetween theelectrodes isnotopen, re-gap theelectrodes.
7. LetthemilliVoltreadingstabilize, thenbegintheanalyticalrun.
DETECTORS
HID - Helium Ionization Detector
