Hi Wasiu,

I trust that you checked the colomn with a Cl-standard to make really sure it is Cl?

If yes:

a) Could it be an overload of the colomn, shifting retention times?

b) Run a blank with all your equipment as usual, maybe its a contamination somewhere?

c) run pure standards of all possible ion in your sample to find the bug :-)

Regards

Stefan

Yes i did check with a chlorine standard and it looks like its chlorine (same retention time and all).

When i run blanks, i do detect some chlorine, but its pretty low ( around 0.2 ppm or even less.with my sample however, i've gotten as high as 32ppm (at low pH)

In terms of standards of possible ions, i'm not sure there are many possibilities in terms of ions....I use Zerovalent iron as a source of Ferrous and then my target compound is perfluorooctane sulfonate (PFOS) which has a straight chain with fluorines attached to carbons and then a sulfonate end.

I'll bet your samples DO contain chloride. It's hard to find real materials that aren't contaminated with some. It could be from handling, for example.

Try Beilstein's test - I believe it's sensitive to the 50-100 ppm chloride range. Assuming you have enough sample(s) to spare. Dry it down to about 1/10 to enhance the sensitivity.

Are you using suppressed ion chromatography or non-suppressed? What is your eluant? Under certain conditions you can pick up bicarbonate, which elutes similarly to chloride.

Thanks John and Mark. I am using suppressed IC and my eluent is a mixture of 0.8M Sodium Carbonate and 0.1M Sodium Bicarbonate.

Certain of the organic acids elute near chloride. Don't remember which one off the top of my head, but acetate is a well-documented interference for fluoride, and several of the others elute concurrent with the inorganic ions.

Thank you Dr. Dasgupta.

That was something i obviously did absentmindedly but i have now taken note.

Wasiu, you can try this: run five blanks, see the response, then you run 5 samples of lowest standard, evaluated the response. If the situation continues, take a sample of your eluent and mesure. With this options you can watch and identify if the problem is the column, you have memory efect or finally the eluent.