# Methods to quantify lead(II) concentration in water on the ppm/ppb level

While there are several ways to quantify metal concentrations in water, a lot of them are only specific to select metals. For example, there is the orthophenanthroline method for quantification of Fe(II) concentrations via spectroscopy. How can lead(II) concentrations be determined using a similar spectrophotometric method?

If spectroscopy isn’t the most efficient way to quantify these concentrations, is there a better way to do it?

The salt used to release $$\ce{Pb^2+}$$ ions into solution is $$\ce{Pb(NO3)2}.$$

Russian interstate standard GOST 18293-72 "Drinking water. Methods for determination of lead, zinc and silver content" (PDF in Russian) suggests to use sulfarsazene (plumbone), which forms orange-yellow complex with lead(II). Reported method sensitivity (spectrophotometry): $$\pu{0.5 μg L-1}.$$

A brief review in English [1, p. 315]:

To determine lead in solid particles of industrial facilities, natural waters, biological objects and salts, sulfarsazene is used (4''-nitrobenzene-1'',4-diazo-amino-1,1-azobenzene-2''-arsono-4-sulfoacids). While it is less sensitive than dithizone , it has a number of advantages: it is water-soluble, easy to handle and needs no cyanide as masking agent. But, it has insufficient reaction selectivity. Manganese, nickel, copper, zinc, mercury, cadmium, iron, zirconium, and other elements interfere with the determination. The methods developed on the basis of sulfarsazene require a preliminary ion separation; for instance, lead is separated by extracting with dithizone solution in carbon tetrachloride …

Study of the reaction of sulfarsazene with lead ions points to simultaneous participation of the lead cation with triazene and arson groups in complex formation. Polarographic investigation confirmed the existence of lead bonds with the o-arsonotriazene group of the reagent, and cleared up the azo-group contribution to the formation of the complex which may be due to coordinative bonding with lead atoms. The role of the nitrogroup as an electrophilic substituent that improves the mobility of the hydrogen atom of the aminogroup was experimentally confirmed. The structure of the resultant compound is as follows:

GOST 18293-72 also includes polarographic method for lead detection using the dropping mercury electrode. Reported method sensitivity: $$\pu{10 μg L-1}.$$

### References

1. Roeva, N. N.; Savvin, S. B. Spectrophotometric Determination of Minute Lead Contents of Natural and Industrial Objects. Reviews in Analytical Chemistry 1986, 8 (4). DOI: 10.1515/REVAC.1986.8.4.313.
• Does the method sensitivity refer to the concentration limit in which the coloured complex follows Beer’s law? – Thunderbolt114 Apr 1 '20 at 23:45
• Moreover, is there a purchase link online? The name seems obscure. – Thunderbolt114 Apr 1 '20 at 23:54
• @Thunderbolt114 Yes, the limits are for the quantitative determination, and the calibration curve is plotted using lead(II) nitrate at $λ_\mathrm{max} = \pu{500 nm}$. – andselisk Apr 2 '20 at 6:43
• @Thunderbolt114 As for buying, it seems that you would need to go with Russian or Chinese suppliers. Being listed in CRC Handbook of Organic Analytical Reagents, sulfarsazene still isn't a popular reagent in the West. – andselisk Apr 2 '20 at 6:45
• I’ve been trying to search for an affordable pricing for this reagent but haven’t stumbled upon any suppliers. Might you know of any site/supplier? – Thunderbolt114 Apr 2 '20 at 7:41