DX-120 ANIONS SENSITIVITY CHANGES

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Hello everyone:

I use a Dionex DX-120 IC with a AERS500 (4 mm) conductivity suppressor and AS-14 (4 mm) column for anion determinations (F , Cl , NO2 , Br , NO3 , PO4 , SO4) with CO3/HCO3 as eluent.

Normally I calibrate with 7 stds at the start, I run about 80 samples of waters and in the end I pass my QC sample of recovery with very good results for years.

It recently started to happen that the QC sample began to get very high, so after that I re-injected the stds and observed that the sensitivity has increased for all anions by 40-50%

I thought it was a problem in the detector electronics inside the mainboard so we changed the board, but the problem persists.

Also note that the conductivity of mobile phase changes from the typical 17 uS to 20-25 uS.

Has anyone had a similar problem or can you think it may be happening?

Thanks and best regards
Flavio
You do not mention if you tried replacing the column itself. We have seen similar behavior after running a series of highly acidic samples (mining waste) and no amount of backflushing restored column performance. Upon replacing the column and running eluent for a bit our calibration standard came back to within 5-10% of its prior values.
Thanks for your answer, it's true, it does not probe changing the column, however, this happens systematically whenever the equipment is used, at first the peaks have a certain area and with the passage of the hours the area increases. When I have another column available I will try. Thanks and regards.
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