[Judas68]

Hello everybody!

I am working in isotopic geochemistry, and am trying to develop a new chromatography method (with ion exchange resins) to separate some trace metal elements (from solid samples) to measure them via MC-ICP or TIMS techniques.

During one of the steps of this method, I use some diluted H2SO4 (2N) associated with peroxide (0.1% v/v) to wash the resin (ca 1mL of resin in my columns), and then I switch to diluted nitric acid (2N) to elute the elements I want to measure from the resin.

The first volume of nitric acid I load onto the resin (1mL) goes to garbage as the elements I want to measure only come after 1.5mL of elution with nitric acid. So it should push the interstitial remaining sulphuric acid out of the columns.

The problem is that, when I dry down my eluted solution at the end of the procedure (I need to change the solvent), there is always one drop of remaining liquid that doesn't dry (at 80˚C). Given that it is sticky, and slowly evaporates only if I increase the drying temperature at least above 180˚C, I assume it is some remaining sulphuric acid. The problem is that it takes a very long time to evaporate it...

So I tried to increase my first elution step (the first mL of nitric acid that is supposed to push the sulphuric acid out) from 1 to 1.5mL, but I still have some remaining sulphuric acid. I can't increase this volume to more than 1.5mL or I will begin to loose some of the elements of interest.

I was thus wondering if maybe there is a way (with the help of a catalyst or something) to increase the evaporation rate of this remaining sulphuric acid. Do you guys have an idea?

[Borek]

Do you have to wash with sulfuric acid?

[Judas68]

yes, I don't have the choice, it is the best way to get rid of the most interfering elements with the resin I use (other resins/acids associations are way less efficient).

[curiouscat]

Heat? Vacuum?

Blow a stream of dry air over it?

Neutralize it somehow preferably into low boiling or gaseous products?

[Judas68]

I've tried the heat, it works, but takes something like two days at 230˚C (my containers only go up to 250˚C). I work in a clean lab, and the only thing I have are basically hotplates, so no vacuum or air blowers.

Given to the concentration of the acid it will need a significant amount of base if I want to neutralize it, and as I am working on trace elements, I would like to add the less reactants as I can.

But I guess I won't find any better solution...

[curiouscat]

A vacuum is really your best option. Not sure why it is so hard to get. Most places have a ready vacuum line or manifold. With a decent vaccum you should be able to lower that BP to around 150 C or so at least. 

[Arkcon]

Sorry to hear its so difficult to neutralize the sulfuric, because that would convert it to a salt, which won't be an oil hanging around.  Perhaps you can try to identify the trace impurities by ion chromatography?