Little shoulder after the peak (half height of the peak)

[lwyyeung]

Hi,

I am now using a ICS 2100 with an AS20 analytical column, ASRS300 (4mm). Recently, I got some problems in peak shape for fluoride and methanesulfonic acid; it is not tailing but some little shoulder. I replaced the column and suppressor; however, it is still there. (https://www.dropbox.com/s/zihh3wxs2odp3 ... togram.pdf)

Can you advise what should I do?

Thanks,

Leo

[mattmullaney]

Hey Leo,

It's been a while ago now (almost four years), but I have found lots of "Big Seven" anion stock standard solutions from vendors that were "contaminated" with a preservative that eluted underneath fluoride...two vendors were kind and patient enough to supply lots of the solvent they used to make their standards. On those occasions, the "contaminants" were traced to less-than-ideal lots of preservatives from the vendors supplying the vendors that prepared the stock standard anion solutions we purchased...if that makes sense.

If you have some clean NaF, it may be worth the time to prep it and run with your own high resistivity water for your piece of mind. I've not run methanesulfonate routinely in my past, but the same may apply...if you have the time and the reagent(s) on hand.

Oh...and also, you can inject eluent...to review another potential cause.

[lwyyeung]

Thanks Matt,

I prepared the fresh NaF and Methanesulfonic acid from bottle; the shoulders are still there. Probably, there are some other unknown reasons.

Leo

[tom jupille]

Try running a chloride standard. Does the chloride peak show the same kind of shoulder?

[John Guajardo]

Hi Leo,

That little peak could be acetate. Is your analysis isocratic or gradient? What is your flow rate and starting eluent concentration? Please look at the chromatogram in section 5.5 (page 22) of the AS20 column manual (http://www.dionex.com/en-us/webdocs/12034-Man-065044-05-IonPac-AS20-Jun12.pdf). They start with 5mM KOH and hold it for 5 minutes before ramping up. This separates the acetate and fluoride.

[M Farooq]

What are your starting hydroxide conditions? If you have another IC column with a different selectivity and higher capacity, you can check if your sample has an additional component or not. The column is unlikely to generate an artefact, since the suppressor removes most of the system peaks. It may be worth trying to inject your deionized water as well.