[Ba] by IC in the presence of SO42-

[Arne]

Hi all,

we are having an interesting issue here. We want to determine [Ba2+] in samples - up to 0.1 wt%. However, there may be sulfate ions present or the Ba may even be present as BaSO4.

How would you suggest preparing the samples to ensure solubilization of the Barium ions and not damaging the IC column?

Thanks!

Arne

[Hollow]

Interesting question.

Probably you need to dilute the samples that much to get below the solubility of BaSO4 (appr. < 10 µmol/L = 1.37 mg/L)
Don't know if this will still be ok with your LOQ.

Or with the solubility product of BaSO4 (1.1x10-10) one could calculate the max. SO4 concentration for an expected Ba concentration.
e.g. a sample with 1 mg Ba2+ / g (=0.1%) dissolved in 1 L (->Ba 7.3 µmol/L) the corresponding SO4 concentration could be 15 µmol/L

So if you can dilute the samples so that the SO4 is below that, the Ba should be in solution (if I remember my study well...)

So maybe another thing would be to trap the SO4 on an anion-exchange resin to exchange it with something that Ba is more soluble with
(OH- may still precipitate but at much higher concentration). Maybe one could load the anion-exchange resin with halogen ions (like chloride or bromide) or with NO3-.

I don't know if or how this would interfere with the IC separation/detection.

[Arne]

Hi Hollow,

thank you very much for the input. We cannot dilute to 2ppm Ba2+ but I do like the anion exchange idea quite a bit. I'll follow up on that and post an update here.

[DR]

I'm thinking this is a titration problem - add sulfate to ensure an excess, do gravimetric titration for the ppt. Calculate Ba as weight fraction thereof.

[Consumer Products Guy]

I was thinking atomic absorption spectrometry or ICP.

[Hollow]

Hi Hollow,

thank you very much for the input. We cannot dilute to 2ppm Ba2+ but I do like the anion exchange idea quite a bit. I'll follow up on that and post an update here.

depending on the ratio, it may also be an option to trap the cations, flush the SO4 and elute the cations again. Similar to "classic" SPE

[Hollow]

Another question keeps me thinking and I haven't considered before.

When do the Ba and SO4 get in contact with each other during your sample prep?

I mean, if they are contained as a mixture of solids (different salts), then I expect that you won't be able to dissolve it at all, because as soon as the two salts are dissolved the BaSO4 will just precipitate. Then the good old gravimetric determination seems the only way. Like DR suggested, add more SO4 to fully ppt. the Ba.

I don't know if BaSO4 can be dissolved again with a digestion with some acid/alkaline, to be measured by an instrumental method, if the accuracy of the gravimetric method is not sufficient.

So one should try to find a way to selectively dissolve the sample with e.g. two immiscible solvents (I don't know if such exist, e.g. form some Ba-organic complex and extract it into an organic solvent?)

Maybe you need a combination of dissolve in a big volume, get rid of the SO4, then concentrate the Ba again...

[Arne]

I know this is really late, sorry, life has been busy: Here's the update - we ended up using x-Ray spectroscopy to quantitate Ba in the samples. It provided acceptable accuracy. Thaks to all you chimed in. The direction AAS/ICP was the same line of thought we pursued.

[lylegordon]

Another option here depending on how many samples you need to process is just to use instrumental neutron activation analysis. Should get better precision and sensitivity than XRF and less concerns with solubility/digestion like AAS/ICP.