Selenium Speciation

[laurimc]

Anyone done selenium speciation on IC? I know it's best done with IC-ICP-MS, but I don't have all that equipment.

So far I have an RFIC Dionex set up with column AS18 (as recommended by Dionex) and I can get a nice separation of selenite and selenate in blank water as low as 10ppb. When I add in some interferents to mimic sample water (i.e. ~500ppm chloride and sulfate) I completely lose the peaks, even when spiking at 100ppm SeO3 and SeO4.

I'm looking into sample pre-treatment with silver to bind chloride and barium to bind sulfate, but I fear that I will lose selenium in the process.

Anyone have experience?

Thanks!!

[iceyuser]

Interesting problem. All I can tell you is to be careful using Cl removal without the subsequent OguardII H Ag removal cartridges. I tried this, and I must have contaminated my autosampler with Ag because I have very bad carry-over for halogens right now.

[Chris Pohl]

iceyuser,

What injection volume are you using? You might be able to get away with such samples if you inject a smaller sample.

Chris

[iceyuser]

Chris, I was using a 50 uL partial loop injection. I tried washing the sample transfer line out with DI, but the problems persists. I've ordered more tubing. I was thinking about washing the line out with somewhat concentrated nitric acid, but I don't know if that would be bad for the tubing (reaction?). In general I seem to have problems keeping the autosampler line tubing clean. This may be related to the fact that I'm measuring ions in serum, where most applications are environmental waters. I'm wondering if using a small amount of EDTA or solvents in my rinse line would help keep the tubing cleaner. I'd be interested to hear thoughts on that. . . not to take the focus away from selenium speciation too much.

[Chris Pohl]

iceyuser,

It sounds like you may be right about the serum contamination problem. We occasionally hear that sample introduction systems get contaminated with biopolymers from certain samples and introduce bias effects that mainly effect cation analysis but sometimes also effect anions (especially if the sample and standard pH are different). You might want to try a hypochlorite treatment of the sample introduction system (but make sure you bypass the columns).

Chris

[iceyuser]

Thanks Chris, this is good to know