25
FIDOperation
The flame ionization detector, FID (Figure 20), is a selective detector because it only
responds tomaterials that ionize in an air/hydrogen flame. This condition covers a very
broad range of compounds, however.An FID / PID combination often is used for petroleum
or volatile analyte applications.
In an FID, the combustion of hydrogen and air produces a flame.When an organic com-
pound enters the flame; the large increase in ions produced ismeasured as a positive signal.
Because response is proportional to the number of carbon atoms introduced into the flame,
an FID is considered a quantitative counter of carbon atoms burned.
10
Among the detectors
discussed here, an FID has the largest linear dynamic range – nearly five orders ofmagni-
tude. The FIDwill detect most carbon-containing analytes at a sensitivity of approximately
0.5ng/µL.
Properly set gas flow rates are important to achievingmaximum sensitivitywith an FID, and
preventing the flame from being extinguished (flame-outs). Generally, the total flow to the
FID is 300mL/min. to 500mL/min., of which the hydrogen flow plus the carrier gas flow is
approximately 30mL/min. The balance of the flow (make-up gas) typically is nitrogen.
The carrier gas and hydrogen gasmix in the FID jet. Capillary columns require a small jet
(0.011 inch ID) whereasmost packed column applications are compatiblewith a larger jet
(0.018 inch ID). Jetswith even larger ID are available for applications involving packed
columns that exhibit higher bleed.
Capillary Adaptable FID Jet
for Agilent 5890/6890/6850GCs
(0.011-inch ID tip)
(Similar toAgilent part # 19244-80560.)
Description
qty.
cat.#
qty.
cat.#
Standard
ea.
20670
3-pk.
20671
High-Performance (Silcosteel
®
-Passivated)
ea.
20672
3-pk.
20673
Capillary Dedicated FID Jet
for Agilent 6890/6850GCs
(Similar toAgilent part #G1531-80560.)
Description
qty.
cat.#
qty.
cat.#
Standard
ea.
21621
3-pk.
21682
High-Performance (Silcosteel
®
-Passivated)
ea.
21620
3-pk.
21683
Capillary FID Jet for Agilent 5880GCs
(Similar toAgilent part # 19301-80500.)
Description
qty.
cat.#
Standard
ea.
21637
High-Performance (Silcosteel
®
-Passivated)
ea.
21638
PackedColumn FID Jets for
Agilent 5890/6890/6850GCs
0.018-Inch ID
(Similar toAgilent part # 18710-20119.)
qty.
cat.#
qty.
cat.#
Standard
ea.
21694
3-pk.
21695
High-Performance (Silcosteel
®
-Passivated)
ea.
21696
3-pk.
21697
0.030-Inch ID
(Similar toAgilent part # 18789-80070.)
qty.
cat.#
qty.
cat.#
Standard
ea.
21688
3-pk.
21689
High-Performance (Silcosteel
®
-Passivated)
ea.
21686
3-pk.
21687
Figure 20.
Components of a typical FID
Collector
FIDJet
Heater Block
Ignitor Castle
Electronic Interconnect
Electrometer
Air
Make-upGas
H
2
Ignitor Castle
