ECD - std checks failing

[scbowman]

My current problem with my 6890GC is that when we run a series of samples the signal is increasing to such an extent that only one standard check passes after the calibration. We run an external standard calibration before each run and a standard check after every 4 samples. If we are lucky the first check will pass our 20% acceptability range. (Side note: some standards contained in the standard check do actually pass but the majority do not). I will also add that the ECD's inlet was recently completely replaced with new gas lines, gas filters, charcoal filters, the inlet itself, everything. This has happened often enough to become a pattern and I would appreciate some help/suggestions as to how to figure out what is causing this and how we might rectify the situation. Agilent was stumped since the entire inlet system had been recently replaced.

[vballchemist]

I had this problem recently on 2 different 5890 systems. (See my post) I think the solution finally came down to cleaning the ECD cells ( and refoiling if necessary) and then giving plenty of bake out/equilibration time for the ECD's to stabilize. How old are your ECD's? When were they serviced last? A Typical symptom of ECD's in need of maintenance is increasing response.
Good Luck

[scbowman]

Thanks for the response. The instrument/ECD were bought from Agilent in 2003. I think my company got them in October of that year. We had a preventive maintenance from Agilent in September 2004, but I don't know that they did anything to service the detectors. I think that they just checked its response, which was fine. Is the maintenance of the detector simply a bakeout for a certain amount of time or do we need to have it serviced by Agilent?

[vballchemist]

If Agilent did PM at your site then they probably did not do a thorough cleaning of the anodes. Depending on usage and sample types being analyzed on the ECD's, 1.5 to 2 years is about the time to clean the cells. I believe Agilent has a program for this. I use CJ Bruyn (check out their web site(http://www.cjbruynco.com), they determine if a cleaning is enough or if the foil needs to be replaced.

[scbowman]

Thanks for the information. I will look into this.