[fuzzfactor]

X-ray fluorescence detects elements based on their characteristic electromagnetic spectrum when irradiated with x-rays.

Not very much like a mass-spectrometer which creates a characteristic pattern of masses resulting from the test material as it is manipulated by the electron ionization or chemical ionization process. Where ions are detected across the atomic mass range of the particular spectrometer, forming a characteristic pattern or "spectrum" across that range.

Actually more jewelers and gold dealers than ever are using the x-ray guns professionally for bulk assay on an everyday basis. There are some handhelds which may be sensitive enough for trace analysis in food, but that requires a whole nother level of dedication beyond identification of metal objects, not just in technique and training but "laboratory" preparation as well.

The first obstacle would be convincing an owner of an instrument having capable specs, to embrace usage for things other than gold and silver assay. Then seriously pursue mastery of the instrument more so than ever to accomplish decent detection of low levels of lead and other metals like chromium, mercury, cadmium, etc.

[pfdietz]

The concentrations of lead being discussed here are as much as 1000 ppm or even higher.

[kragen]

Quoting perihelions's comment above:

[1] https://pubmed.ncbi.nlm.nih.gov/25214856/ ("Contaminated turmeric is a potential source of lead exposure for children in rural Bangladesh" / "Results: Lead concentrations in many turmeric samples were elevated, with lead concentrations as high as 483 ppm")

[fuzzfactor]

>as much as 1000 ppm or even higher.

The higher it is, the less likely for challenges in detection, and/or interference from background.

>lead concentrations as high as 483 ppm

SSDD.

Shouldn't be that hard to detect at that level which is way above ppb. There are a number of reliable methods.

However if the Minimum Detectable Level for a particular test procedure was only 500 ppm or above, one of these samples would report just as clean as a sample having no lead whatsoever; < 500.

MDL's like this which vary among different test methods do need to be carefully compared to the toxicity levels being screened for.

That's another one of the confounding aspects to be aware of.

Depending on circumstances, I may or may not prefer a different calibration session for each of these two levels, even though they are both within the same order of magnitude.

Either way ideally I would be preparing NIST-traceable reference materials at the proper levels for comparison & confirmation. Not much differently than I would do for the benchtop models and the forklift models of x-ray units. And to really get down into the ppb levels that's when the ICP/mass-spec comes in handy, that's a benchtop unit itself, too big to fit on a regular desk though. However you don't really get the most out of the ICP without a huge cryogenic tank of liquid argon out back so you can "consume mass quantities" ;)

With a handheld x-ray unit, if you are only assaying gold & silver it may be fine to send it back for calibration once a year, if the pawn shops even do that. For food testing I would want more of a laboratory-style analytical procedure and calibration which is concurrent with materials being tested.

[kragen]

I agree that hand-held XRF guns should be able to detect such lead levels, and I believe that was in fact what the police used when they did the publicity stunt in the Bangladesh market. At any rate, it sounds like you know a lot more about the question than I do. I was only disputing pfdietz's comment, "The concentrations of lead being discussed here are as much as 1000 ppm or even higher."

[fuzzfactor]

Good call because results should be expectd to be all over the ball park, and I think even higher numbers could be found. But no amount of lead is supposed to be acceptable.

>sounds like you know a lot more about the question

SSDD says it all without explanation, but here's a little.

Until you've spent lots of time at the bench, it's not easy to understand why a 1000 and a 483 might just be the same sample tested in different labs.

Or even the same lab on different days.

If so that would look even more embarrassing when my arbitrary reporting convention < 500 is applied.

But it's actually not unheard of to get a positive and a negative on the same sample even with some of the most sophisticated equipment

Explaining the rest of the story could fill textbooks, but the operators wouldn't be reading them anyway :\

So that's the most important thing to know, besides the actual spectrums which are table stakes.