ECD Baseline Troubleshooting

Answer

This Information Applies To: All Agilent GC systems with, µECD detector

Issue: 

The micro Electron Capture Detector (µECD) shows a higher than usual baseline signal.

Warning: The ECD utilizes a radioactive source.

• You may not open the Electron Capture Detector (ECD) cell unless authorized to do so by your local nuclear regulatory agency. Do not disturb the four socket-head bolts. These bolts hold the cell halves together.

• Never eat, drink, or smoke when handling an ECD.

• Always wear safety glasses when working with or near open ECDs.

• Wear protective clothing such as laboratory jackets, safety glasses, and gloves, and follow good laboratory practices. 

• Wash hands thoroughly with mild nonabrasive cleaner after handling ECD.

Tips: For more information, also see ECD Safety Data Sheets and ECD Management and License Information.

Steps to follow:

Tips: Presence of oxygen in the system will rise the baseline signal. Oxygen can either enter through leaks in the GC, leaks in the gas tubing or through contaminated carrier or make up gases. Thus, those causes show similar symptoms.

 Leak

If the baseline is > 1000 Hz, it is an indication that there is a leak. 

1. Check for leaks at column fittings, ECD, and inlet. Information can be found in the Troubleshooting Manual of the corresponding GC model. 

2. With the detector capped: Turn the oven (fan) on and off. If the signal changes significantly, suspect a crack in the make up gas line. A broken make up gas adapter weldment is a common failure cause. Stop here and evaluate replacing the make up gas adapter. Call Agilent support for further assistance.

Caution: Baking the detector with a leak could damage the ECD cell.

        3. If you have identified and removed the cause, perform a bake out of the inlet, the column, and the ECD. Otherwise follow the next steps.

      
Figure 1 Make up gas adapter

Contamination

If the baseline is very high, there is probably low-quality gas plumbed to the GC. This contamination could be from the carrier or make up gas streaming through the ECD.

Per the Agilent Site Prep sheet, we specify 99.9995% purity for the gases used with ECD. When working with an ECD, it is highly recommended to have gas filter or traps on the gas lines that are as close to the GC as possible. If problem includes ghost peaks, humps, or elevated baseline, contamination may be an issue.

1. To evaluate if the contamination comes from the inlet or column, turn off the carrier gas. Remove the column from the ECD and put a blank nut in the ECD. If the baseline begins to come down, the carrier gas or an impurity at the inlet was likely causing the contamination. 

2. If the baseline is still high with the carrier gas removed, the contamination is coming from the make up gas. 

   1. There are a few tests you can do to check the make up gas and the tubing associated. With the column still removed from the detector and a blank nut installed at the detector, raise the oven temperature to 275 °C. This action will heat the make up gas adapter - you should see the baseline rise. Often if you run a "Blank run" with the column disconnected, you will see a profile much like column bleed as the oven ramps if the make up gas adapter is contaminated. 

   2. If the make up gas is contaminated, get a new and clean tank. If you believe that the gas is now clean, you can bake out the detector with a high make up gas flow to thermally clean the lines and purge the system.

Tips: Be aware that contamination can often enter the gas lines if the gas tank is pulled too low. Gas tanks should be changed before they are fully empty when using the ECD to avoid the 'dirty' gas on the bottom.

 

Caution: Baking the detector with a leak could damage the ECD cell.

Bake out procedure:   

a. Remove the column from the detector and put a blank nut in the ECD. Set the ECD temperature to 400 °C and the make up gas at 100 ml/min. 

b. Continue the thermal bake for one hour, then drop the ECD temperature to 300 °C and make up gas flow to 30 ml/min and see if there is any improvement in the baseline.

c. If the new gas is clean and the gas lines from the tank to the instrument are not badly contaminated, you might see improvement within an hour.

d. Continue the bake-out and purge overnight or a weekend if the contamination is bad. 

        3. If the contamination cannot be cleaned using the thermal bake-out and purge, you will need to begin replacing parts at the gas line.

a. The smartest way to replace parts is starting at the gas tank. First replace the gas regulator, the copper tubing, and the gas traps/filters. You should see some baseline improvement after purging the make up gas.

b. If the contamination is still too high, contact your local Agilent support representative for troubleshooting.

c. If the baseline remains too high, the ECD cell has to be replaced.

Tips: It is critical that the flow path is changed out systematically in cases of bad contamination.  If there is contamination in the gas and you replace the make up gas adapter, you will likely see improvement of the baseline for a short time. Once the contamination is swept through the flow path, the make up gas  adapter will become contaminated again.

     

Tips: The older an ECD is the higher the baseline will climb.

Figure 2. Typical ECD life cycle.

A new ECD will likely have smaller peaks than an aged ECD, this is normal behavior. It is also important to note that a new ECD will have a substantially lower noise than an aged ECD. The ECD can be cleaned thermally, but eventually, even the thermal cleaning will not be able to bring the baseline down. Consult with your local Agilent support representative if a new ECD should be considered. 

Tips: Reference values for ECD signals of each GC model can be found in the Troubleshooting Manuals.

Learn how to effectively operate your Agilent 7890 and 8890 GC: Agilent 7890 Series GC with OpenLab CDS ChemStation Edition Agilent 8890 GC with OpenLab CDS e-learning paths available from Agilent education.