Rhodizonic Acid and Silver Citrate?

Question

I have used some of those lead check swabs from 3M. I used them on some ceramic tile and received strange results. I called the tile manufacturer who was insistent that lead had never been used in their operations. After talking with 3M they asked me to send a picture, which I did. After looking at the picture the 3M lab told me that they did not believe the test to be positive for lead but didn't explain the color I observed.

I realized I had cleaned the floors with a cleaner which contained silver citrate as a preservative. Would the silver ions have reacted with the rhodizonic acid? What color would this have produced? I observed a pinkish color (definitely not red. More pink/purple) in some areas I tested.

I can include a picture if it would help.

Answer 1

I investigated silver rhodizonate, among other ions, in my master's thesis. Being a high symmetry oxocarbon $(D_\mathrm{6h}),$ it exhibits many interesting spectroscopic properties. The results are published in the Journal of Raman Spectroscopy.^[1] It indeed forms a dark substance, whose absorption spectrum can be altered if the sample is ground. This phenomenon deserves further study!

Reference: 1. Gonçalves, N. S.; Santos, P. S. Resonance Raman spectroscopy of rhodizonates: Evidence of low-energy transitions in the solid state. J. Raman Spectrosc. 1995, 26 (5), 363–372. DOI: 10.1002/jrs.1250260507.

Answer 2

$\ce{Ag+}$ reacts with Sodium Rhodizonate to form a Black colored compound - but only in a neutral or weak-acidic environment.

$\ce{Pb^{2+}}$ should give you a Blue-Violet color (or Scarlet if we're dealing with a weak-acidic environment); therefore, I don't think you're dealing with a lead contamination.

Reference: Feigl, F.; Suter, H. A. Analytical Use of Sodium Rhodizonate. Ind. Eng. Chem. Anal. Ed. 1942, 14 (10), 840–842. DOI: 10.1021/i560110a034.