Chloride ion background

[joelyue]

i am using the Dionex DX500 system and recently i am getting this Cl peak in my blank runs which didnt appear before.

I tried to find the source of the contamination but in vain. I have tested by removing the ion trap column, refreshing the eluent(ie UPW), tested the UPW for Cl(no Cl present), flushed and cleaned the concentrator and even flushed the whole system overnight.

After doing all these the peak is still there. Where else could i have missed or what else can i try? Your suggestions would be a great help.

[tom jupille]

What are you injecting as a "blank"?

[joelyue]

i injected UPW as my blank.

[tom jupille]

I assume "UPW" means "ultra-pure water" (as opposed to, say, "Underground Professional Wrestling" per http://www.acronymattic.com/UPW.html ).

The most likely explanation is that you actually have some chloride in that water. So:
- what was the source? (bottled? in-house water system?)
- have you compared with a blank from another source?
- is there any chance someone left a sweaty fingerprint on the inside of a beaker (I'm not joking; I've seen it happen)?
- is the water for the blank the same as the water used to prepare the mobile phase?

[bisnettrj2]

Per Tom Jupille - I assume his chloride contamination isn't doing a suplex off the garage and into his system, so we can rule out the Underground Professional Wrestling contamination. Perhaps he's using water from a Millipore or similar system - and that system's filtration/purification capability has been surpassed? I would try getting an outside source of pure water to test, to ensure you aren't seeing a generic contaminant issue from a fouled lab water supply.

[joelyue]

Sorry for the confusion. It means UPW = Ultra Pure Water. The source comes from the Ultra Pure water system in my plant. I have tested the blank sample in another system using NaOH/NaCO3 eluent and it shows very little or no Cl ion content.
This current system uses U.P. Water as eluent.

[tom jupille]

That seems to leave the glassware or the autosampler/injector as the most likely sources of contamination.

What happens if you run a series of blanks? Does the chloride peak stay about the same size or does it get smaller? If it gets smaller, especially an "exponential" pattern of decrease, that implies a source of chloride trappped somewhere in the injector (perhaps a poorly assembled connecting fitting?). If the peak stays the same size, that implies that there actually *is* chloride in your water, and I'd be inclined to look for contaminated glassware.

[Mark Albertson]

Hi joelyue,

Further to Tom's comments, if you are using an Autosampler on this DX-500 system especially with glass 1-2ml vials please change to a polypropylene or plastic vial. Some brands of glass vial are high in ionic contaminants due to the releasing agents used in the blow molding of these vials. Transfer pipettes either plastic or glass used to transport samples into smaller vials as mentioned above can also introduce ionic contamination. Soak all vials over a 24 hour period in a clean enclosed vessel or tray with type I water to remove any contaminants, then rinse with fresh DI Water prior to use. Avoid transfer pipettes use wide mouth vials if possible and pour your sample from the primary sample vessel directly into the sample vial. Also remember type I water generation necessary for IC work is a phase reduction clean up process. Depending on the feed water quality you will get a reduction at each clean up phase RO Type I<Electro-deionization (ELIX) Type2 <Ion Exchange with D2 lamp Type I water. Should you have high Ionic contaminates, TOC or Bio-film at any point in the water pretreatment process this will effect your blank. Check you system prefilters and RO membrane for their last replacement date, if it has fallen outside of your prescribe service schedule replace these components. If your water system lacks any of the pretreatment steps above this will explain the presence of ionic contaminants. There are some good articles available from Millipore on this subject including application note 007 (its not a joke that is the app note number).

[joelyue]

Hi i have found out that the contamination came from the concentrator. Cl levels in my blanks slowly reduced to 0 after i changes the concentrator inlet filters.