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DETector Engineering &Technology, inc.
486N.Wiget Lane,Walnut Creek,CA94598USA
telephone: (925) 937-4203
fax: (925)937-7581
DEI
Agilent type
jet Inside baseweldment
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HYDROGEN
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e-mail:
innovations inchemicaldetection
DET Retrofit Equipment for Different Brand GC Instruments
GENERAL CONSIDERATIONS -
DET ion sources
2Different Styles of FlODetector Bases and Jet Locations
are available mounted in either a 3/4 inch hexagonal
VarlanfThenno type
shaped flangeor in a1/4 inch tube. The hexmounting is
jet extends above base
used inall DEThardwarestructuresaswell as inAgilent
689017890
NPDequipment, whereas the tubemounting
is used in NPD hardware structures designed by
Thermo Scientific and SRI Instruments.
Retrofit DET hardware structures are designed to
custom fit ontoanFID/NPDdetectorbasealreadyon the
GC, so that the existing detector heater block and
pneumatics lines can be used.
Generally, GCFlObases have one of the 2 basic styles
illustrated in the figure. For the VarianlThermo type
base, the jet extends above the detector base, and a
OET retrofit includes a ceramic tipped jet and a tower
VarianfThermo type base is easier to fit with DETNPDfTlD
structure that fits down over the
jet,
An ion source
detector tower structures.
mounts into the top of the tower such that it is
positioned in close proximity to the topof the jet. ADET retrofit tower in this case is identified as anNPDITID/FID
assembly because all variations of thosemodes of detection can be achievedwith the appropriate choice of ion
source type and detector gases.
For the Agilent type FlObase, the jet is located down inside astainless steel weldment, and aDET retrofit tower
extends down into and on top of the weldment. With this retrofit configuration, the ion source and surrounding
collector electrode are constrained to a location several centimeters downstream of the top of the jet. Unlike an
FlO, the jet in anNPD is not required to support aself-sustaining flame, so DET recommends using awide bore
jet that allows capillary columns of 0.53 mm diameter or less to be inserted clear through the jet to a location
closer to the ion source. ADET retrofit tower for this type ofdetector base is identified as aRemote FlOassembly
because it can beused for NPDITIOdetectionmodes aswell asRemote FlOand FTIDmodes ofselectivelywhich
use the column pulled down to the jet top and a self-sustaining flame ignited at the jet.
AGILENT 6890/7890 GC MODELS -
Agilent designed the 6890 NPD hardware to accommodate the hex
flanged ion sources manufactured by DET. Consequently, any of the different type ceramic ion sources
developed byDETcan bemounted into6890/7890NPDhardwareand used to achievemodesofdetection beyond
just NPD. A limitationof
689017890
NPDequipment is that the associatedAgilent NPDelectronics is not optimum
in providingConstantVoltage heatingof the ion source instead of preferredConstant Current heating, aswell as
being limited to a very low polarization between the ion source and collector electrode. As an alternative to
powering ion sourceswithAgilent's NPOBeadVoltage supply, DEThas astand-aloneCurrent Supplymodule for
more stableConstantCurrent heatingof ion sourcesplusaselectionofboth lowand highpolarizations.Whereas,
a lowpolarization is fine forNPdetection, higherpolarizationscan provide10 times bettersignal to noise forother
modesofselectiveTIDdetection. OETalso recommends using awide bore jetwith 689017890NPDequipment so
that capillary columns of 0.53mm diameteror less can be inserted clear through the jet to a termination closer to
the ion source. This eliminates any possible degrading interaction of sampleswith the jetmetal; it eliminates jet
orifice clogging from complex sample matrices; and eliminates the need to ever replace the jet. DET also
recommends that 6890/7890NPD users avoid using the Adjust Offset featureof the electronics as that inevitably
operates the ion source hotter than needed, and shortens ion source lifetime.
