Let me first address the largest drawback of chemical tests, they do not test below the surface. They cannot replace an inspection designated in the 1992 law known as Title X and they cannot determine legally if there is "Lead Based Paint" present.
They can however, determine lead containing paint's presence since this is not an arbitrarily defined metric for paint contamination.
With that lets get into what different chemical tests for lead are.
The first chemical test for lead was known as Turner's Test.
Turner's Chemical Lead Test
is a mixture of a strong acid, typically sulfuric acid, and potassium Chromate, which, if you've ever seen Erin Brockovich, Potassium Chromate is a source of hexavalent chromium which is carcinogenic. This is probably why it was not fit to be sold to the general public to detect lead in their homes. As it would cause damage rather than simply fixing it. Potassium Chromate in the presence of a strong acid assimilates with lead forming lead Chromate which is a yellow color you can see that below.
Sodium sulfide
is another test used for about a hundred years and it identifies lead through sodium sulfide interacting with lead to form lead sulfide also in the presence of a strong acid. This reaction turns the lead black or brown depending on the concentration and its main drawback beyond its moderate toxicity is the offensive odor it produces. It smells like rotten eggs because of the sulfur and it is also very difficult to apply to a surface. In order to test using this method, the lead has to be placed into a container and then the sodium sulfide added to the liquid in that container making some destruction of the wall necessary for a test to be conducted.
Sodium Rhodizonate
is a method that is much more friendly to the user. It can be conducted with a strong or weak acid. Sodium Rhodizonate disassociates and the Rhodizonate moiety connects with the lead to form Lead Rhodizonate which is red.
This red to purple color has been known for years thanks to 3M promoting lead check extensively and their tagline "red means lead". Sodium Rhodizonate can accurately detect levels of lead down to about 500 parts per million.
Methylammonium Halides
Methylammonium Halide compounds are typically used in solar cell manufacturing, its discovery was made by a team working at Amolf in the Netherlands a splinter of that the original team who worked on the conversion of a lead compound found in paint to the luminescent version used in lead detection, filed patents for its detection by this method in 2021. I've worked with them for about a year now I currently distribute their products on amazon.com it's known as Lumetallix.
They've touted this as a method for detecting lead that can achieve nanogram sensitivity which is true in highly controlled settings, I have found is not something relevant to the detection of lead in paint. The major benefit of glowing lead tests over sodium Rhodizonate based lead tests is that sodium Rhodizonate is unstable when in solution. making a spray bottle of a Rhodizonate based test not feasible.
When I created Scitus brand Rhodizonate swabs about 5 years ago through my company Spirochaete Research Labs, I overcame the challenge of depositing sodium Rhodizonate onto a swab head by mixing it with anhydrous carrier fluid I used different types of alcohols and finely divided Sodium Rhodizonate ensured uniform deposition onto the swab head. By allowing consumers to activate the swabs with household vinegar, it allowed me to decrease the price per test from about $5 for a single 3M lead check swab to about $0.50 for one of my Sictus swabs. all while maintaining the same degree of accuracy on the swab's results. And this, in my opinion, has increased the accessibility of lead testing kits to those who need it the most.
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