Troubleshooting Contamination Problems; Ensure Clean Gas Supplies; Isolate Problem To Carrier Or Makeup Gas Supplies - Agilent Technologies 6890 Series Service Manual

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Electron Capture Detector (ECD)

Troubleshooting contamination problems

Persistent problems with high background or ghost peaks with temperature

programming are almost always due to contamination from dirty samples,

consumables, or the carrier/makeup gas systems.

Begin with the procedure in chapter 5, Volume 3, of the Operating Manual. If

this procedure, which can be performed by the user, does not solve the

problem, perform the following steps.

Before continuing, verify that the supply gases are of adequate purity.

Carrier and makeup purity must be >99.999%.

After confirming purity, verify that the tank regulators have stainless

steel diaphragms (equivalent to Agilent part no. 8507-0407).

Install new 1/8-inch copper supply tubing—part no. 5180-4196. Many

times "clean" tubing from other sources has caused high ECD background.

At the same time, install new traps in both the carrier and makeup

supplies. Place the moisture trap (part no. 5060-9084) closest to the tank

and the indicating oxygen trap (part no. 3150-0528) closest to the GC.

Leak test the entire plumbing setup very carefully.

Determine what components of the apparent contamination are from the

carrier vs. makeup systems in the GC. Sharp, well-resolved peaks that elute

during a temperature program with no injection are from the carrier/inlet

system. Broader "humps" in the baseline are usually from the makeup system.

Overall high background (>500 Hz) can be contaminated gas from either the

carrier or makeup supply or a contaminated detector cell.

Remove the column from the detector and inspect the installation of the

makeup gas adapter. It is quite common for the adapter to be installed too

low. To check this, measure from the bottom of the 1/4-inch Swagelok nut to

Agilent 6890 Gas Chromatograph Service Manual

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