How to Clean an FID

Answer

This Information Applies To: Agilent 6850 A/B, 6890 A/N/Plus, 7820A, 7890A/B, 8860, 8890 Gas Chromatographs with Flame Ionization Detector (FID)

Issue:

The cleaning of the Flame Ionization Detector (FID), may be required in the following scenarios:

Preventive or periodic maintenance.
Resolving performance issues of the detector:
- High background, noise, or spiking of baseline.
- Problems to ignite the flame.

Steps to follow:

Tools Required:

Torx T20 screwdriver (p/n 5182–3465)
1/4 x 5/16-inch wrench (p/n 8710–0510)
1/4-inch nut driver (p/n 8710–1561)
Tweezers

Consumables (as needed):

Depending on their condition, replace the detector consumables, e.g., FID jet, PTFE insulators, ignitor, silicone ring, etc.
Cleaning kits are available for more convenience:
FID Maintenance Kit (p/n G1531-67000)
Includes:
- PTFE Collector Insulators
- Silicone Rubber Base Gasket
- Ignitor
- Cleaning brushes for Collector
- Cleaning Wires for Jet
FID Cleaning Kit (p/n 9301–0985)

Includes:
- Reamers
- Wire mini brushes
- Handle

Warning: Cool the detector and oven to a temperature below 80 °C. Wear safety goggles when working with compressed gases.

Caution: Always wear clean gloves while handling any parts that go inside the GC or the detector. All inner parts of the collector assembly should be treated as ultra inert.

Cool the detector and oven to a temperature below 80 °C.
Turn off the detector and uninstall the column from detector.
Disconnect the ignitor.

Figure 1 Ignitor connection
Uninstall the ignitor by turning counterclockwise with a 5/16-inch wrench. Check state of copper washer and replace if necessary.

Figure 2 Ignitor uninstallation

1. Copper washer
Using a Torx T20 driver, remove the manifold assembly by unscrewing the three screws in an alternating manner.
Lift the collector assembly straight up. Wiggle softly while doing so to avoid damaging the interconnect spring.

Figure 3 Removal of collector assembly

1. Interconnect spring
Unscrew the knurled brass nut by turning counterclockwise.

Remove the knurled brass nut, the castle with its washer, the upper insulator, the collector, the lower insulator, and the silicone rubber gasket at the bottom of the collector assembly.

Figure 4 Parts of the collector assembly

1. Knurled brass nut, 2. Castle, 3. Slot for interconnect, 4. Spring washer, 5. Collector, 6. Upper PTFE insulator, 7. Lower PTFE insulator, 8. Silicon rubber gasket

Tips: Note that the longer end of the collector faces down.

Inspect, clean, or replace the parts.

The collector body can be sonicated in a beaker with soft detergent in water for 5 minutes, cleaned with a brush or cotton swab.

Figure 5 Cleaning of the collector
Do not sonicate the FID castle, just rinse or wipe. Otherwise the PTFE coating will be damaged.

Rinse all parts with distilled water and finally rinse with reagent grade methanol or hexane. Let all parts air dry.

Caution: Do not expose the silicon rubber ring to organic solvents as they might dissolve the material.

Warning: Methanol, hexane, and their vapors are flammable. Methanol and hexane can influence health permanently. Check safety data sheets before use and wear appropriate protective clothes. Discard solvents in appropriate containers.

Set up the collector assembly after cleaning: Re-insert the lower insulator, the collector, upper insulator, castle with washer and knurled nut. Tighten by hand. Slip the silicone rubber gasket at the bottom of the collector assembly. (Figure 4)

Tips: The longer end of the collector faces down.

Tips: The lower and upper insulators are the same why they can be placed indistinctly. The insulators have one completely flat side and one with a border around the central hole, the border points towards the ends of the collector.

To remove the jet, use the 1/4-inch nut driver and lift it with tweezers.

Figure 6 Jet removal

1. Jet 2. Interconnect spring

Caution: Avoid touching the interconnect spring to not damage it.
Examine the detector base for any particles - blow out the base with compressed air or nitrogen. (Use safety goggles.)

Figure 7 Top view of detector base.

1. Inner detector entrance.
With a pipette bulb, blow from the bottom to remove all particles or debris. (Use safety goggles.)

Figure 8 View on the detector base.

1. Outer detector entrance.
With an unfolded paper clip, you can remove pieces of graphite that may be stuck in the bottom of the detector.

Figure 9 Cleaning of detector bottom.
Clean the jet with a thin steel wire (0.010 inch, can also be the string 1 of a guitar) or replace it.

Figure 10 Cleaning of jet with a wire.

Caution: Scratches on the FID jet affect its performance. If you choose to clean the jet, be sure not to scratch or bend the jet.
Reinstall the jet. (Step 11, Figure 6) If the jet is new, hand-tighten until it stops and give 1/6 of a turn with the nut driver. If it is a re-used, hand-tighten until it stops and give it a slight squeeze, then 1/16 of a turn with the nut driver. Do not tighten the jet too much as you can break it.
Reinstall the collector assembly. (Figure 4 in reverse)
1. Place it on the body of the detector and press it carefully down. (Step 6, Figure 3 in reverse) Take care not do damage the interconnector spring. The interconnect spring should “pop” into place and lay in the groove of the collector body!
2. Fit the three screws of the manifold assembly and tighten, install the ignitor, and connect it. (Steps 3–5 in reverse)
Install your column according to the Reference guide.
Turn on temperatures, pressures, and flows, let the detector warm up at least to 250 °C degrees, light the flame, and test performance of your FID.