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In a previous question, I learned that we can detect lead with sodium / potassium rhodizonate, giving a nice purple color when reacting with pure (elemental?) lead.

But in the paint, lead is primarily used in the form of salts such as lead oxide, lead carbonate, lead chromate...

What if the lead in my paint is not pure, but a salt? Would sodium rhodizonate react with such salts? (I insist on sodium vs potassium, since it's cheaper to get). And if not, how can I detect these salts?

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According to Ashley et al, "a rhodizonate spot test kit [for] in-situ testing of lead in paint... can be used for screening (i.e., qualitative) purposes." The test is sensitive not only to metallic (elemental) lead, but also to lead compounds used as pigments. However, the reference cited also states that the sulfide and rhodizonate tests have a high incidence of false positives.

Sodium, potassium or even cesium salts of rhodizonic acid should be equally effective, since the active species is the rhodizonate ion, but be aware that the sodium salt is less stable in water solution and should be used within a few days.

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