[pajamallamamama]

Thanks in advance for any help given...

I'm trying to determine the best method for dissolving a white lead alloy for elemental determination by ICP-OES. Currently I am using a mixture of nitric acid/tartaric acid and a hot plate to get this done. However, there is some disagreement regarding the tin content so I am troubleshooting my method. Another lab I consulted uses a microwave with a solution of HNO3/HCl and after cooling, HF is added. They achieved a tin result that was within specification (~6 wt%) whereas I am consistently yielding a higher result (~8%). Also, I have dissolved a similar certified white lead alloy alongside my sample and meet the appropriate specification limits.

Happy and willing to answer any questions that may help resolve this discrepancy. I don't have access to a microwave in my lab and have not had any experience with one either. Is there something in my dissolution process that could be yielding a higher tin value? Is there something in the microwave method that could be yielding a lower value? Any positive interferences for tin by ICP-OES? All of the tin wavelengths are giving similar results.

Thanks again for any help.

[Corribus]

The biggest difference between microwave and hot plate digestion is throughput, safety, and convenience. If you do a lot of ICP-OES, it's worth the investment. Not sure why the HF is necessary, usually it's only needed for silicates. Avoid at all costs if you can, that stuff is nasty. White lead is mostly carbonate and hydroxide. I would think strong acid would be sufficient unless it's a really impure mineral. If it's a geological sample that has a lot of other rock/sand/soil in it, this might be why the other method uses HF. If it's a pretty refined lead carbonate/hydroxide, it probably isn't necessary.

What instrument are you using? Our ICP-OES provides common spectral interferences for most elements. Probably yours will too.

I assume you are using high quality (trace metal at minimum, optima better) acids? Have you checked to see whether your tartaric acid has contaminants in it? We were doing a digestion once that used a weird acid in the matrix and it was found to be the source of a trace impurity that was giving us headaches. Any idea what the tartaric acid is for?

This is totally a stab in the dark, but has anyone tried an ashing method? Carbonates are prone to pyrolysis.