Chromatography Forum

Hi Guys,

We have recently been presented blindly with a method of analysis which involves in-direct UV and using Ion-exchange chromo.

The system we have is an agilent 1200 DAD and i believe this method has been run using this system before.

Mobile Phase: 24mmol Nitric Acid(65%) in Water

Test Solutions are simply prepared in water.

The peak that is obtained is Negative (as expected) although the peak shape is terrible,- a large peak tail is observed.

Does anyone have any ideas as to why this could be happening. I have very limited experience with Ion exchange and 'Zero' with indirect UV detection.
I know i have not provided a great deal of information as i am not so sure what you would need to know in order to remedy this, but its a great thing to solve this issue so any help is greatly appreciated!

LC!

The column used is IC-PAK A HR 6um, 75 x 4.6 mm

Some possibilities:

- your column has developed a head space or has a partially-plugged frit. In that case, if you have multiple peaks on your chromatogram, they will all show the same sort of tailing.

- you are overloading. In that case, the tailing will vary with sample size.

- your are seeing "system peaks" interfering with your analyte. In that case, injecting a water blank will show the system peak.

Maybe your peak would look better if you add some base to your samples. When you prepare the samples in just water, some of the acid that you are analysing will remain protonated (depending in the pKa of course).

or is this far-fetched?

Without ay information about the analyte it is impossible to tell a reason for the large tailing (except those related to bad column performance).

You are using an anion exchange column and a pretty acidic eluent. Is your analyte still in anionic form under the eluent conditions? Is the analyte compatible to 24 mmol/L nitric acid?
How is the peak shape if you make up the sample in eluent?