I am doing a project in my highschool about analysing C/N and C/S ratio of finger nails of various ages and sexes. Please suggest me a way to do this. I don't know where to start, I know the various methods of estimating the amount of N or S present theoretically. Please provide info that how should I dissolve the nails etc.

I will be doing my experiment in a nice lab which has got all necessary equipment that I might need, so please answer without considering the limitations of my lab.

I got the idea by this website: https://pubmed.ncbi.nlm.nih.gov/18424895/

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    $\begingroup$ Sorry, not a doable project at a high school level. Of course elemental analysis can be done for carbon but sulfur content is very tricky. Sulfur is also done by elemental analysis but when the amount of S is very small, it becomes tricky. Secondly will cost a lot, you will at least to do duplicates to get a reliable measurement. Think of other projects which are doable. Secondly use Google Scholar and see what others have done before. $\endgroup$ – M. Farooq Mar 31 '20 at 14:00
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    $\begingroup$ @M. Farooq OK Sir I might not do the sulphur analysis so can you suggest me a more exhaustive and accurate approach for nitrogen content $\endgroup$ – PJ The MADAO Mar 31 '20 at 14:08
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    $\begingroup$ Nitrogen is also determined by elemental analysis. There are commercial instruments called CHNS analyzers. They burn the organic compound, and analyse the gaseous products, CO2, NO, SO2, by gas chromatography. Many universities may have this service. You will have to go through your teachers and see if they have access to this service. They need to pay as well. Have a look at the Wikipedia article en.wikipedia.org/wiki/Elemental_analysis $\endgroup$ – M. Farooq Mar 31 '20 at 14:15
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    $\begingroup$ There is no nascent hydrogen! It is an incorrect notion: see the short wiki article on “Nascent hydrogen”! $\endgroup$ – Ed V Apr 2 '20 at 13:48
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    $\begingroup$ ''I will be doing my experiment in a nice lab which has got all necessary equipment that I might need, so please answer without considering the limitations of my lab." We actually do need to take into accoount the limitations of your lab, since we didn't we'd just assume you had a machine like this, which is found in labs that do C/N/S analysis: eu.leco.com/product/928-series. Once you've completed the calibration, the machine is simple to run—just load the sample and press a few buttons. Analysis takes only about 5 minutes/sample. $\endgroup$ – theorist Jan 24 at 19:17

These analyses are difficult to carry out at a high school level. Nails are not soluble in any solvent. They must be burned and the gases coming out are analyzed and weighed. To burn them, they have to be mixed with a great excess of copper oxide, put in a long horizontal glass tube, heated from below. A current of oxygen gas should be sent through the glass tube, and the gas should be absorbed first by solid $\ce{CaCl2}$ which absorbs $\ce{H2O}$, then by $\ce{NaOH}$ which absorbs $\ce{CO2}$. By weighing the $\ce{CaCl2}$ and $\ce{NaOH}$ flasks before and after the operation, you can calculate the amount of $\ce{C}$ and of $\ce{H}$ contained in your original sample. To measure the amount of nitrogen of your nails, you have first to destroy them by sulphuric acid, then add them to $\ce{NaOH}$ and some Dewarda alloy (mixture $\ce{Al}$, $\ce{Zn}$) have it boiled to liberate $\ce{NH3}$ gas, and then absorbed this gas containing $\ce{NH3}$ into a solution of an acid like $\ce{HCl}$ or $\ce{H2SO4}$, and then titrate the remaining acid to deduce the percentage of $\ce{N}$ in your original sample. This can not be easily done in a high school lab, slowly.

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    $\begingroup$ Maurice, a good rendition, however, could you comment on whether the procedures you outlined are particularly suitable for determining very small differences, in say, sulfur presence. $\endgroup$ – AJKOER Mar 31 '20 at 12:17
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    $\begingroup$ @ Ajkoer. The traditional chemical analysis I described has been used for all $\endgroup$ – Maurice Mar 31 '20 at 12:20
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    $\begingroup$ Thanks for the reply. For others, I would point out that the use of "NaOH and some Dewarda alloy (mixture Al + Zn) " is also a de facto use of nascent hydrogen. $\endgroup$ – AJKOER Mar 31 '20 at 12:26
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    $\begingroup$ @ Ajkoer. The traditional chemical analysis I described has been used by all chemists in the 19th and 20th century to obtain the chemical formula of a new compound. But it is not adapted to very small differences as you stated. There exists several ways of analyzing Sulfur. The simplest is Liebig's approach : A known amount of substance is fixed on a platinum grid and burnt in the middle of a big bottle containing 6 liters $\ce{O_2}$. Later on, a solution containing 10% $\ce{Na_2O_2}$ is added, then the whole is acidified by HCl, and the ion sulfate is precipitated by $\ce{BaCl_{2}}$. $\endgroup$ – Maurice Mar 31 '20 at 12:32
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    $\begingroup$ @Ajkoer. Yes. Dewarda alloy produces nascent H in NaOH solution. $\endgroup$ – Maurice Mar 31 '20 at 12:33

Some suggestions:

First, collect the fingernail samples by applying a nail file to a subject's nail. This creates a fine powder.

Second, precisely weigh the sample and place the nail powder in distilled water.[EDIT] Here is a possible dissolution of nail path per a reference that should be verified in its accuracy, which claims:


Water is great for your overall health including your nails, whereas fizzy drinks like Coke are not so good. In fact Coco Cola is kind of scary. If you place a piece of nail in a bottle of Coca Cola it will dissolve within 4 days, that’s how corrosiveness it is!

where the chemistry is likely conditional on the presence of the Aluminum (some electrochemistry at play). More interesting, do nails, in time, dissolve in an Aluminum can containing just Phosphoric acid, carbonated water, sugar and perhaps some NaCl, in a closed system (no gas escape)?

Third, I like a nascent hydrogen approach here to breakdown the nail powder (research the Marsh Test to detect small amounts of arsenic). So, further add Al/NaOH (or Zn/HCl) and collect the vapors in dilute H2O2 (which has been pH adjusted to a recorded value at over 7). [EDIT] This step may have to be re-evaluated based on revised Step 2, perhaps just neutralize with NaOH/H2O2.

Depending on the test equipment available, a simple comparative test would be to investigate the evidence/concentration of a visible sulfur suspension (a light-based test), as a pH check alone, for example, for any significant decrease in pH (a measure of increased acidity from sulfur-based acid formation) would not likely be sensitive enough for small differences in sulfur concentration.

One could refine the process starting with test samples containing but small differences in the amount of sulfur presence, as a feasibility check.

[EDIT] To be honest, I (and apparently at least one other) have doubts on the potential feasibility of this project. However, with the to-be-confirmed electrosynthesis dissolution of human nails, I would have to upgrade your chances especially based on your possible access to equipment to confirm relative elemental composition.

  • $\begingroup$ Thanks. Will I be able to use the gases evolved in the coca-cola exp, also can you edit your answer without considering the limitations of my lab since it has got almost all necessary equipments that I might need, $\endgroup$ – PJ The MADAO Mar 31 '20 at 14:03
  • $\begingroup$ Also instead of marsh test can you suggest more arsenic confirmation tests $\endgroup$ – PJ The MADAO Mar 31 '20 at 15:03

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