Adding concentrated mobile phase into samples

[vockhead]

Hello,

I'm fairly new to ion chromatography, and I was just wondering something: I know generally when samples can be evaporated to salt and then reconstituted into the mobile phase you're able to get a much flatter baseline and improve your peak detection by a bit.

I was just wondering why nobody ever recommends, instead of evaporating the sample, just adding a concentrated version of the mobile phase so that after mixing it should closely match the mobile phase through the column and improve the baseline.

Is it just that the extra step/errors usually aren't worth the hassle, or is there something else more fundamental that I'm missing.

Thanks.

[mattmullaney]

Hi vockhead,

Actually, the former EPA 300.0 anion method recommended this practice...I don't know how widespread the notion is overall of adding concentrated eluent to the samples and standards in an IC run to lessen the "water dip". Here's a link:

http://water.epa.gov/scitech/methods/cw ... _300_0.pdf

Section 4.0, and in particular, Section 4.2. Idea makes a great deal of sense to me if you're measuring ions (such as fluoride or formate) that are near the "water dip", their peaks will be easier to integrate.

Best Wishes!