Charge Aerosol Detector signal reduction

[Charles A. Burger]

Current problem involves a Corona CAD (early generation)

The problem is that a compound and it's subsequent impurities, which I have been working with for months, is now responding at roughly half of what it has been throughout this project.

This issue started after I mistakenly pumped mobile phase through the column at high flow (5 ml/min) for 30-45 seconds. I noticed the high pressure and opened the purge valve which I though was already open.

Thermo is of the opinion that the detector is just fine since the diagnostics check out. However, when I explained that all UV responses (which I am collecting also) show no change for this compound and it's impurities, Thermo gave one possibility, but still maintains it is probably not the detector.

Has anyone else experienced loss of signal response and not been able to recover it after you "wash with 50/50 H2O/Methanol?"

[Kreall]

I have encountered the same problem. The funny thing was that it changed during the sequnce. We called the Dionex service to check it out. They scratch the top of their head and took the CAD and they send it to the manufacturer. In 2 weeks we had a new CAD detector...

CAD detecter was ESA 70-6186A if it helps enything. Hope someone will figure it out what is going on with yours.

[Gerhard Kratz]

5ml/min flow? My recommendation is to check the column. What particle size and dimensions?

[Charles A. Burger]

5ml/min flow? My recommendation is to check the column. What particle size and dimensions?

Yes I accidentally hit it with 5 ml/min. Pressure was near 400 bar when I noticed it and opened up the purge valve, which should have been open in the first place. Column dimensions: 25cm x 4.6mm 5um particle size.

One of the first things that popped into my head was that I damaged the column. However, the corresponding UV captures of the injections before and after the "accident" have been equivalent.

And now as of this morning I have data that suggests the CAD is just fine. I ran the standard Performance test that Thermo service agents run and my Caffeine response is right where it's suppose to be. Which prompted me sigh loudly.

Bad news is that I have a problem that only Gandalf the White could help me with. Good news, when I do solve it I'll be that much smarter.

[LCwatcherGE]

Hi all,

5ml/min is much too high for each CAD, where 2ml/min is the max. flow rate!
Seems that the CAD is or has been flooded and some debris still remains inside the nebulizer chamber (impactor) and/or the mixing chamber, including the charger head.
The CAD should be PM'd and thouroghly cleaned inside. Also the inner gas flow rates should be checked if there's a blockage.
Afterwards the former performcance should be acheived again.

Greetings,
Joern

[dibyendughosh]

Hi Charles,

I am the Global trainer for Charged Aerosol detectors.

There might be a probable partial flooding on to the detector.
The acceptable flow rate is 0.2 to 2 mL/Min
Also it may happen that the Electrometer filter was little wet, eventually dried and the responses are lower than expected.

It you can let me know the following:

The current at

1. 100% water without column at 1 mL/Min flow to the detector
2. 100% Methanol without column at 1 mL/Min flow to the detector

Also while running the detector (ESA Corona Ultra/Dionex Corona Ultra/ Dionex Corona Ultra RS) go to the diagnostic screen and list out the following:

1. Total Flow
2. Flow Ratio
3. Ion trap voltage
4. Icorr
5. Vcorr

After looking at the values i can probably help you out.

By the way may i know the engineer who attends the CAD calls, just for information.

[Charles A. Burger]

Also it may happen that the Electrometer filter was little wet, eventually dried and the responses are lower than expected.

Now that is a little piece of information is new to me and very interesting. At the moment the system that has the detector is in use. When available, I'll perform those instructions and get you the data.

Thank you for reading beyond the first page. Till then...

[dibyendughosh]

I will be happy to help you Charles