Dionex DX-100 IC Peaky Baseline

[admiralbrown]

I'm stumped by this one. I use our IC to test waste oils for Chloride and Sulfate. On Friday the instrument ran fine, one of the samples I ran was possibly from tire pyrolysis, it was a very smelly even after combustion. On a side note the ICP's internal standard was only on third of normal during that sample, but that is a different issue and I got around the problem.
Friday the IC ran fine. On Monday the baseline was not stable, it was not a flat line. Also my sensitivity dropped, my 2.0 ppm standard read between 1.3 and 1.5 ppm.
I have changed the guard filters, tried using an older column and guard column. I tried cleaning the detector with 5 ml of Hexane then Methanol then Ethanol and finally deionized water. I tried using a different injection loop. And I first tried to clean our self-regenerating suppressor with 0.5N H2SO4 and then bought a new self-regenerating suppressor from Dionex. I tried cleaning all connections in the back of the instrument. Nothing has helped and my baseline while in the right place is very spiky.

Any suggestions on what to try next would be appreciated.
Thanks

PS The reference to my 1987 Cosworth Sierra in my signature just lets you know I am a gearhead and know how to turn a wrench and troubleshoot a 25 year car. And I was able to keep my old Perkin Elmer Plasma 400 running for 19 years before getting the new ICP. I don't want to just throw money buying new parts or buying an old DX-100 on eBay and randomly swapping out parts.

[admiralbrown]

I forgot to mention the unit requires nitrogen at between 90-110 PSI and I have a nitrogen regulator set at 105 psi.

[kfemrite]

Hello-

You have shown a great deal of perseverence/resourcefulness/self-sufficiency...

The symptoms might be related to contamination from a recent sample, or could be completely unrelated. If the problem involves an instrument component failure, you could be facing a challenge in finding replacement parts -- many of the components are no longer manufactured.

Troubleshooting would likely require special tools and expertise. A call to the Customer Care Group (1-800-346-6390) would be a good step to assess whether you'd be better off paying for a service call or seeking a more modern (and more supportable) instrument.

[admiralbrown]

kfemrite
Thanks, I try to make all my stuff last, see my picture in the dictionary under frugal.
The pyrolysis sample is a good candidate for contaminating my column except: One, the peakiness was still there when I replaced my current column with my old column. Two, the pyrolysis sample was at the start of the run on Friday, and the whole run was fine, it was on start up on Monday that I noticed the problem.
Of course it could be a dirty detector and I don't have a spare to try to compare.
That said, I've been flushing the system with a 10X concentration of eluent. My mix is a combination of Na2CO3 and NaHCO3. If anything I am losing sensitivity and and my baseline is getting worse.
The instrument is obsolete. My IC doesn't see enough use to justify a new one, possibly a used instrument. Of course it wasn't until my Plasma 400 ICP was on its last legs before I got the new Optima 8000.
Tomorrow I'll talk to my boss about a tech call to "Dionex, now a part of Thermo"

There always are instruments on eBay if I want to try just randomly replacing parts. I just don't like doing anything blindly.

[vockhead]

There is a cleaning method that I have had some success with in the past for conductivity detectors. Essentially, they are just passivated stainless steel electrodes in an inert plastic encasing. With the power turned off, you can pass 20-30 mL of 6 N Nitric acid through the conductivity cell, and then flush it for about a day or two, just to be safe, since you are using a lot of organic material and you wouldn't want the nitric to react with a large amount of it.

It is a harsh cleaning method, and I would probably save it until you are at your wits end and thinking scrapping the conductivity cell anyway. We had a build up of organic material all throughout our system when someone decided to use tap water to make their mobile phase. This was pretty much the only way to clean it all out since propanol/hexane didn't seem to be cutting it after two weeks.