Chromatography Forum

Hi all,
I am running a Cation method using Grace column (100 x 4.6mm) for some cations such as Li, K, Ca.. (in ppm range).
The mobile phase is just 3mM methanesulphonic acid.
The method suggest using only conductivity detector. And there are no peaks, the baseline is about >1000.
I am not sure if the problem is because of lacking ion suppressor or anything else.

Thanks for any help

Which detector are you using?
You will get negative Peaks. Offset the background and amplify the signal.

Thank you for your help.
It's a TraceDec, a contactless condutivity detector.
The baseline is too high, so I try to reduce the concentration of mobile phase, then the peaks do not come out !

Reducing the eluent concentration does not improve the response factor but prolongs the retention time only.

Thanks. I understand now !
I will try again and see.

Hi Markus,

It's not done yet. When I run the buffer (3mM), the conductivity rises up to max (1903.78) and does not change even I inject quite concentrated std. I reduce the buffer concentration to only 16%, then it reduces to apx. 1800 , but still not peak.
I am not sure if something is wrong, is it because of the water quality ?

Dear thohry

Knowing this , I assume that your detector is not capable of handling high conductivities (around 1 mS/cm).
In a first look I could not find any limits in conductivity of your detetctor.
Using 0.5 mmol/L MSA yields in much longer retention times. And you are still not sure that you are working in the linear range of your detector.
Please check the working range of the detector first. for non-suppressed IC a linear range up to 2 mS/cm is required.
Bestregards
Markus

Thanks Markus,

The TraceDec CCD can only measure 1903 uS/cm at max. and the mobile phase is always higher than that. I wil try water of better quality to see it can help. The water I am using reads 130uS/cm on the detector, I think it's not good.
Thanks again for the advice.
Thohry

3 mmol/L MSA should still be below 1000 µS/cm.
Water with 130 µS/cm I call dirty. Ultrapure water should read 0.05 µS/cm or (with dissolved CO2 from the air) at least below 1 µS/cm.

Is there the possibility to adjust the cell constant of the the detector? If yes, you might lower that value. The set value might be by far too high.

3 mmol/L MSA should still be below 1000 µS/cm.
Water with 130 µS/cm I call dirty. Ultrapure water should read 0.05 µS/cm or (with dissolved CO2 from the air) at least below 1 µS/cm.

Is there the possibility to adjust the cell constant of the the detector? If yes, you might lower that value. The set value might be by far too high.

Thanks for your precious comment. I have check the water purification system, they did not replace the cell quite a long time ! Dirty water is the culprit.
It seems there's no way to adjust the detector. It saturates at about 1900 uS/cm
Anyway, to get the peaks out, I have increased the flowrate to 2.5 and it works. Just temporarily because I think the water may contaminate the column !
I have to get the cell be replaced as soon as possible.
Thank you very much Markus

Thohry