So I'm trying to identify a metal in 25 mLs of raspberry juice (hand-crushed) + a bit of KCl, and after running it on CV ultimately yielded unreadable results, I ran it on ASV. There are two peaks. Score!
I concluded that one of these peaks were iron (nevermind how I came to that conclusion). So I spiked it with a certain concentration of Fe(III). The signal reduced. Okay, maybe it was a bit of bad luck, I thought. I spiked it again, running it on the same conditions, deposition time, quiet time, etc. Again, the signal reduced. I up the concentration spiked. Signal still reduces. After several trials, I concluded that there is a definite correlative trend that the signal is being decreased with each iron spiked.
I'm pretty sure that the signal is supposed to INCREASE, but that's not happening in this case. There is a possibility that the peak I chose is NOT actually iron, but this same peak is being lowered with each successive spike. Could there be some sort of reaction that is taking place that I'm not aware of such that the existence of more irons could actually decrease the signal? Maybe it's Fe2O3 that is somehow decreasing the current, but I would imagine successive increases of ferric oxide would still increase the signal in some way. Could it have been that I introduced some iron-sucker with my standard additions? I am completely flabbergasted.
I'm using a gold working electrode with a platinum counter electrode, and am using Ag/AgCl as my reference electrode. Any ideas on why this would be happening would be really, really cool.