removal of nitrates from hydrochloric acid 3

[Japo]

Hello,

We're trying to detect trace nitrates and we've found (unequivocally we believe) that an ultra-pure HCl 37% solution is contributing a certain amount of nitrates. According to our approximate quantization the amount may be within the limit promised on the label (~1 mg/l), but in our application that's too much background noise.

We're not managing to better the original purity ourselves (surprise) by distillation. Can anyone think of some substance that could be added to the solution so distillation may work better, allowing us to purify the HCl+H2O leaving the nitrate behind? Perhaps a cation that forms a very stable salt with the nitrate but doesn't react with the chloride?

I'm not chemical by education so I may be missing something very obvious or talking nonsense, but our chemists can't think of anything right off the bat either. Thanks in advance.

 

[StoneCold]

Japo
How about filtering a small amount through powdered carbon?
What about kaolin clay?
Neither may work but it is worth a try, and relatively cheap.

Regards
StoneCold

 

[ash9144]

Sulfamic acid is added to remove nitrates from sulfuric acid. You could use the same but it would leave some sulfuric acid behind. The nitrates are decomposed to nitrogen.

 

[Latexman]

Have you gone back to your supplier of ultra-pure HCl 37% solution and told them you want a product with NO nitrates? They may have heard this before and have a solution.

Good luck,
Latexman

 

[Japo]

Thanks a lot all, I hadn't thought about physical separation or even asking the supplier (Sigma-Aldrich), and I didn't know about sulfamic acid... I'm passing your suggestions along to the chemists.

(We're still giving distillation a go, correcting a few things. Last thing, we hadn't considered that if the batch is small, the HCl concentration in the liquid will drop quite fast when boiling, and so the boiling point will rise to that of the azeotrope (110º C), and in those conditions distillation won't work if the nitrate can go into vapor as acid as we suspect.)