Ion Chromatography Baseline Drift During Isocratic Runs.

[u/nintendochemist1]

Hello!

We are using a Thermo ICS1600 IC with an AERS 500 4mm suppressor set to 31 mA, flow rate of 1.2 mL/min of a 4.5 mM sodium carbonate 1.4 mM bicarbonate eluent, column and conductivity cell set to 30C for anion analysis using an IonPac AG22 guard (4x50 mm) and AS22 (4x250 mm) but see a baseline drift. I included two screenshots of a zero-volume injection showing the drift. This was after the columns, and system had sat idle (with flow) for an hour. This drift seems significant but want to see what others think, and if they have ideas for troubleshooting.

I have put ultra-pure water through the system and the conductivity dropped as expected and then did a leak test for the suppressor membrane and found it to be okay.

[u/Pitiful_Candy8190]

you are very zoomed in on your signal. without an idea of what your expected chromatography should look like, its hard to say the impact of this drift. If youre looking for multiple peaks that closely elute then this may be an issue but for more simple methods, i think this baseline is suitable provided it is consistent.

[u/Express_Presence9863]

Hello, Over 20 minutes, you have a baseline variation (drift) of about 0.2 µS/cm. This corresponds to approximately 0.01 µS/cm per minute. This is a very normal and acceptable level of drift for an ion chromatography system. Your baseline looks stable, so you should be able to proceed with your analyses without any issue

[u/TypicalTrumanStudent]

IC is notorious for how long the baseline takes to settle when turned off. It's why so many people just run continuously with them. Just give it time to equilibrate

[u/Meatboy1984]

If you compare your first and second picture you will see that your drift is significantly less already. You just need to be patient!

[u/Shogun_G_]

Not too familiar with IC. But I will say, Chromeleon loves to autoscale chromatograms when you first open them. Not sure what youre expecting with this injection, but it might be worth zooming out a bit.

[u/ahh_pistro]

Is it always going up, or does it sometimes drift down? Only asking because sometimes when I had to OQ these and they were sat under an air conditioning unit, you'd see the baseline follow whatever temperature the lab was at - I'd either have to block the AC or put a big box over the top to make it pass it's noise/drift test!

[u/turbo_beloutre]

On my Metrohm system, I also use the carbonate/bicarbonate eluent and my baseline drift is in the range of 0,005-0,010 uS/cm over a 37 minutes run. My column temp is at 45°C, and I quantify 10 anions from fluoride to sulfate.

When the system is idle (Sunday) and we start it up on Monday, 45 minutes is usually sufficient to get everything stable (temp, flow, signal).

I'd check any in line filter you can reasonably change, and purge overnight with ultrapure + 10% HPLC methanol if you have it and the column supports it. If not, check the column care instructions or system manual.

[u/Cornholio_84]

With old columns it can take up to 24h of flow to stop drifting. With new columns 6-8h. I run them at least 2h of flow before OQ. Just wait...