Oxalate Contamination

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Hi all,

I test for several organic anions using a Dionex ICS-5000 with IonPac AS5A-5u analytical and guard columns. Oxalate is one of these anions that shows up in our samples and I’m seeing small amounts of oxalate in our DI water blanks (upwards of 10 ppm) prior to running samples, which eventually drops to below 1 ppm after a few injections of DI water. Running 100 mM KOH through the column for an hour prior to this first injection of H20 doesn’t seem to remove any of this residual oxalate that shows up. I’m not even sure where this oxalate is coming from since our end of run control and blank never show any sign of oxalate remaining on the column. From the time we shut off the pump to the next time we run samples is usually a couple days and oxalate builds up on the column in this time. I’m thinking the best way to get around this is to just keep the eluent flowing through the system at a low flow rate on days I’m not running samples? If anyone had any insight on to why oxalate would be showing up like this too it would be greatly appreciated.

You don’t state the nature of your mobile phase. May I assume the tubing is PEEK/PTFE.

What is the material of the sample injector, loop and injection syringe.

Do you have any potential oxalate producing components within the tubing, sample injector, loop and injection syringe.
Kind regards,
Ade Kujore
Cecil Instruments
United Kingdom

email:- ade.kujore@cecilinstruments.com
telephone:- +44 (0) 1223 420821
web site:- www.cecilinstruments.com
Registered Number 909536
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