Hello everyone,

I'm new to chromatography and currently trying to get a Dionex ICS-6000 operational again.
The system was out of commission for over a year due to overpressure building up with no apparent reason and was only flushed with pure de-ionized water for several months before I came here (Eluent Generator and Supressor were off when we started working on the system). The previous operator had left the company and does not seem to have passed on much information..

We have now managed to get a good 0,25 ml/min flow rate again (without overpressure shutdowns) on both the Anion and Cation sides.

Both sides do not yet produce a satisfying chromatogram, though ..

I will here focus on the cation-side :

First the modified system setup:

- Eluent Generator and GradientMixer (GM-3) are bypassed, we use ‚hand-made‘ Methylsulfonic Acid Eluent at 7 or 8 mmol/l (tried both concentrations, it does not seem to make a difference) for isocratic program

- we use ultra pure de-ionized water – which I’m told meets the requirement specified in the manual (0,055 μS/cm)

- Guard Column: Dionex IonPac CG19-4μm, RFIC, 2x 50 mm (we also tried it without the guard column, the chromatograms did look the same)
- Analytical Column: Dionex IonPac CS19-4μm, Analytical, 2 x 250 mm (we tried the old one and a brand new one, chromatograms looked the same)

- Suppressor: Dionex CSRS 300 2mm, operating at 6mA (recommended by the system)


Now to the results.. we tried running several samples of cation-standard, tap water and NaCl.

- background is consistently low (usually under 0,5 μS/cm)
- NaCl produces a single peak at about 4,5 minutes
- tap water produces two peaks at about 4,25 min and 5,5 min
- cation-standard (containing 6 different ions: Li+, Na+, NH4+, Ca2+, Mg2+, K+, in 0,l% Nitric Acid) produces a sort of continuous ‚mountain range‘ spanning from ca. 3,5 min to ca. 7 min retention time. It contains 4 discernible individual peaks at 4min; 4,5min; 5 min and 6 min … presumably the one at 4,5 min should be the Sodium..

I rinsed the column again with acetonitril-containing solution (according to the protocol from column certificate), which slightly improved the separation (generally slightly deeper ‚valleys‘, 4th peak is now separated from the others, but the chromatogram is still not useable).

Any idea how the separation could be enhanced to the point where we would get clearly separated peaks for the different cations would be very welcome :)

As we tried a different (new) analytical column (of the same type), but the results for the standard looked nearly identical, we would presume that something other than the analytical colum is causing the poor separation? We were guessing it might be the Suppressor (as there are not many other devices left on the cation side).

We also experimented a bit with the suppressor current to see if that helps, but there was no improvement of separation with 7, 8 and 9 mA (the values allowed by the system for the given eluent concentration)



The only thing I could think of now is to continue rinsing the column with acetonitril-containing solution (as that was so far the only thing that seems to have had any positive effect), though I’m not very optimistic that this alone will solve the issue…
If the problem should happen to be solved I’ll post an update here in the coming weeks.


Cheerio,

Andreas