# Where is my antimony going?

I work in a trace metals laboratory operating an ICP-OES. I've been having some trouble with the recovery of antimony in a weak $\ce{HCl}$ solution post-digestion.

The antimony is part of a mix of elements in ~$\ce{5\% HNO3}$, 1 mL of which is added to a beaker with ~$\pu{50 mL}$ of $\ce{0.5N HCl}$, then heated at a low temperature for ~10-15 minutes. There is a filtering process afterward using simple glass fibre filters. I've been getting between 60-75% recovery of the antimony, and at least 80-90% recovery of the other elements.

I've been able to find some information regarding issues with antimony and $\ce{HCl}$, and possibly with natural light affecting the stability of the solution, but nothing definitive or on-topic.

Any ideas?

• I'm pretty sure I remember the folks from our ICP lab discussing problems with Sb volatilizing, though I thought that was during higher temperature digestion of solids. Anyway, SbCl3 is fairly volatile (BP ~220C) and ferric chloride will complex it and reduce it's volatility. If I knew the details of how to do this right though, I'd have written a formal answer ;) – airhuff Apr 20 '17 at 0:45
• And, the antimony trichloride is accessible because you have the nitric acid there to oxidize the antimony to the appropriate oxidation state. – Oscar Lanzi Apr 20 '17 at 0:59
• @Oscar - Would the little amount of nitric involved be a player? It's 1mL of 5%. Though I guess it doesn't take much with how strong nitric can be. – Max Power Apr 20 '17 at 2:27
• @airhuff - I'd have to check the actual temperature of the hotplate. It's on one of the lowest settings, and the 0.5N HCl solution involved never reaches boiling. The powdery substrate this test is for does cake up somewhat at the bottom and cause some sputtering. I don't have the option of adding ferric chloride, must follow a pretty straightforward process. – Max Power Apr 20 '17 at 2:29
• @Max also probably not a lot of antimony. – Oscar Lanzi Apr 20 '17 at 9:49