Chemistry Forum

Hello,

I have to write a term paper on the determination of mercury in human hair. I've read quite a few professional articles, but none describe the process in great detail. After reading everything, I somehow came to the conclusion that it would be best to use cold-vapor-atomic-absorption-spectometry. I would dissolve the hair sample in nitric acid and hydrogen peroxide, and for standard solutions I would use a solution of HgNO₃ in nitric acid. After the sample was all dissolved (I hope it would, otherwise I would have to filter it), I would quantitatively transfer it to a volumetric flask and pipet out a certain aliquot (I don't know how much, I would decide based on the concentration range). Then I would reduce Hg₂+-ions to Hg with NaBH₄ or SnCl₂ and determine them by AAS. Und now I'm interested in how exactly this is done. I probably need to heat the sample a bit to get the Hg to vaporize. But since I've never done this before, I'd appreciate it, if someone could describe it to me a little. I am also interested in standard solutions. I probably have to make a reduction there too, so that everything is determined the same? In short, I would like to ask for a short comment and help with this task of mine. Is such a method of analysis even meaningful and possible?

Thanks in advance!

The method is decribed here

Analysis

2.3.2 Mercury Cold Vapor

Inorganic and organic forms of mercury are ubiquitous in the environment, including water and food, and comes primarily from the burning of coal. As a result, it is necessary to detect the concentration of mercury to assess the danger caused by this toxin. Mercury is a neurotoxin and extremely small concentrations (part per billion or part per trillion) and can have detrimental effects due to bioaccumulation in the food chain (increases in concentration as one goes from one tropic level to the next). Several fish species, located in streams downwind from coal burning regions contain significant, and in some cases, dangerous concentrations of Hg. Flame AAS techniques only yield detection limits of approximately one part per million which is inadequate for environmental and food monitoring. The cold vapor technique described below yields detection limits in the parts per trillion range. Equal or even lower detection limits can be obtained by ICP-MS (the subject of Chapter 3 and 4) and atomic fluorescence techniques (a more advanced technique not included in this textbook).

An overview of the cold vapor system is shown in Animation 2.5 where an external glass vessel is used to generate elemental (and volatile) mercury that is passed through a Pyrex/quartz cell placed on the standard burner head. No flame is needed to atomize the mercury, hence the name “cold” vapor technique.

A sample containing digested water, sediment, or tissue that contains cationic mercury (Hg₂+) is added to the external glass vessel, which is then closed and purged with argon to remove any oxygen. Next, SnCl₂ is added via a syringe to reduce Hg₂+ to elemental Hg. The elemental Hg is stripped from the water solution and passes as a pulse of vapor through the sample cell. The instrument is operated in the absorption mode; a hollow cathode Hg source lamp provides a specific wavelength to be absorbed by Hg(g) in the cell. After detection, the mercury vapor passes through a potassium permanganate solution to convert the mercury vapor back to ionic mercury so that no mercury is released into the laboratory environment or into the natural atmosphere. All blanks, external standards, and samples must be analyzed in the same manner. A drawback to this method is that samples must be processed individually, without automation. For each new sample, the argon stream must be interrupted to allow addition of a new sample to the glass container, which must then be purged with argon.

The advantage of the technique is a three order of magnitude improvement in the detection limit. Disadvantages are labor costs associated with digestion and manual instrumental analysis. When numerous samples are routinely analyzed this technique has been replaced with ICP-AES (with a detection limit of 1 part per billion) and ICP-MS (with a detection limit of less than 10 parts per trillion). Cold vapor mercury analysis is still commonly used when mercury is the only metal of interest and economics does not support the purchase and maintenance of an ICP-MS system. The reader should review Animation 2.4 at this time.

A hair mercury test is quick and simple, and only takes a few minutes to complete. It consists of cutting a small section of hair from the back of the head near the scalp, placing the hair sample in a labeled zip-lock bag, then sending it to the public health lab in a pre-addressed stamped envelope

Thanks for the reply.

I'm curious about one additional aspect of the hair sample processing. As I've read, the decomposition procedures are rather distinct, but because I've never done this before, I'm wondering if the decomposition with nitric acid and hydrogen peroxide is so good that no filtration is required, or if filtering is always required. Some authors make no mention of it.

Thank you very much.

I think the decomposition process with nitric acid and hydrogen peroxide always requires filtration, but it's not so good that it doesn't need to be filtered. You should test it yourself to get accurate results. Remember to be very careful with this experiment. Good luck

To convert Hg²⁺ ions to elemental mercury (Hg⁰), you can use a reducing agent such as sodium borohydride (NaBH₄) or stannous chloride (SnCl₂).
Add the reducing agent carefully to the sample or standard solution, ensuring that the reaction proceeds smoothly without excessive foaming.

Neon wrote: ↑Sat Dec 02, 2023 2:59 am Hello,

I have to write a term paper on the determination of mercury in human hair. I've read quite a few professional articles, but none describe the process in great detail. After reading everything, I somehow came to the conclusion that it would be best to use cold-vapor-atomic-absorption-spectometry. I would dissolve the hair sample in nitric acid and hydrogen peroxide, and for standard solutions I would use a solution of HgNO₃ in nitric acid. After the sample was all dissolved (I hope it would, otherwise I would have to filter it), I would quantitatively transfer it to a volumetric flask and pipet out a certain aliquot (I don't know how much, I would decide based on the concentration range). Then I would reduce Hg₂+-ions to Hg with NaBH₄ or SnCl₂ and determine them by AAS. Und now I'm interested in how exactly this is done. I probably need to heat the sample a bit to get the Hg to vaporize. But since I've never done this before, I'd appreciate it, if someone could describe it to me a little. I am also interested in standard solutions. I probably have to make a reduction there too, so that everything is determined the same? In short, I would like to ask for a short comment and help with this task of mine. Is such a method of analysis even meaningful and possible?

Thanks in advance!

I have to write a term paper on the determination of mercury in human hair? Really? Do you have the link to this article? I just heard this information for the first time. Maybe it's because my chemistry knowledge hasn't been upgraded yet

It is appropriate to use a nitric acid-based HgNO₃ solution as your reference solution. To make standard solutions, follow the same procedure as for your sample: dissolve a known quantity of HgNO₃ in nitric acid,Buckshot Roulette and then use a reducing agent such as NaBH₄ or SnCl₂ to reduce it to elemental mercury.

Your proposed method for determining mercury in human hair using cold vapor atomic absorption spectrometry (AASslope) is indeed a well-established and commonly used technique in analytical chemistry.

These recipes are really interesting. Compounds are formed according to certain rules. Solving chemistry problems is really not simple. Scales understand nature and see richness.

Hair mercury levels are notoriously difficult to assess, so use them with caution.