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A document I've been reading states that:

Both the Maximum Contaminant Level Goal and the Maximum Contaminant Level were set at 2 parts per billion because current technology allows public water suppliers to detect and remove mercury levels that low.

But I know of drinking water test strips that detect 0, 50, 100, ... 1000 ppb and are 1,5-Diphenylcarbazide based.

On a chem supplier catalog I've found that 1,5-Diphenylcarbazide can detect up to 0,000002 g/ml, which is 2000 ppb. But I know from a question on this website that the above reagent can detect up to 250 ppb.

And as per urine and blood concentrations we are looking at 10 ng/ml they detect.

So what is the threshold for 1,5-Diphenylcarbazide test and how they detect those minute amounts anyway?

Is there a DIY method of detecting something like 2 ppb at home?

P.S. I am talking about Hg2+ ions, if it is not clear

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    $\begingroup$ I doubt that any water analysis lab would be using 1,5-Diphenylcarbazide strips for analysis. Almost certainly ICAP would be used. // It is also unlikely that most municipal water supplies would have mercury as only $\ce{Hg^{2+}}$. $\endgroup$ – MaxW Feb 27 '20 at 20:42
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    $\begingroup$ In wiki, look up “Atomic absorption spectroscopy” and scroll down to “Cold-vapor generation”. Detection limits are down at the parts per billion level. The chemical stuff is generally not as sensitive, especially test strips. $\endgroup$ – Ed V Feb 27 '20 at 20:42
  • $\begingroup$ Typo: replace “generation” by “atomization”. $\endgroup$ – Ed V Feb 27 '20 at 20:58

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