CLPEX Chat Board

I posted two questions a few weeks ago - thanks to those that responded -I have shared this with my lab people and I think we will be making some changes in how we process with Ninhydrin. . .


In reference to why Ninhydrin prints will sometimes take a few days to appear - After some discussion with one of the people I work with from another agency (Dan G.), he posed the question "Could it have something to do with secretor status?" That somehow the amino acids aren't as "readily available" to react with the Ninhydrin, and might take some time to react. . .?????? I thought it was worth pondering and wondered if anyone has some thoughts and/or knowledge in this area. . .

Hi Julie,

Fortunately for us we work in the same laboratory as Dr Chris LENNARD. To understand how the ninhydrin reaction works you will need to research the relationships between sweat, cellulose, chemical and conditions. The constitution of eccrine and sebaceous gland secretions are varied but we do accept a high concentration of water in eccrine sweat. The relationship between water and paper is clearly understood in that it will migrate through cellulose but the variables of how much and how far the amino acids migrate is not available. The chemical reaction of ninhydrin with the amino acid is understood to be a three phase process resulting in a yield of Rhumanns purple. The optimun yield of Rhumanns purple will vary according to the conditions of temperature, relative humidy and acidity. All these variables are clearly explained in chapter 4.4 of the book Fingerprints and other Ridge Skin impressions by CHAMPOD, LENNARD, MARGOT AND STOILOVIC, worth a read. Regards from Oz. Les

Hi Julie,

sorry for the spelling error, Ruhemann's purple is the correct spelling for the product from the ninhydrin/amino acid reaction. Les

Thanks so much for the helpful information - I'll see what I can do with it!

Julie

Julie, I can share with you what I have been told about Ninhydrin prints appearing a few days later. I have been told two scenarios.

SCENARIO 1: As Mr. Bush said the sebaceous and eccrine material is intermixed and when the print is deposited on the paper the sebaceous oil has a tendency to protect or prevent the ninhydrin solution from interacting with the amino acids. As the sebaceous oils migrate further into the paper fibers, the amino acids are trapped or fixed into the paper fibers. Since the solution ninhydrin is still active it will then react to the amino acids to form Ruhemann's Purple. At a later time.

SCENARIO 2: Most amino acids will react favorably with ninhydrin. However there are a few that will not. These other amino acids for whatever reason are the ones that are sometimes left on the paper. It takes the ninhydrin longer to react to these other amino acids. These other types of amino acids (beta form I was told) can be caused by different diet, stress, disease, or be that person's natural make up. It takes ninhydrin longer to react to these other forms of amino acids.

Now I am not a chemist or molecular biologist, so I can not vouch for these. I am only offerning them as to what I have been told at various times.

If you decide to read CHAMPOD, LENNARD, MARGOT AND STOILOVIC, I would suggest you have a good background in chemistry or molecular biology. Some people that have read it, find it a difficult read since they do not have the chemistry and biology background like most of us do not.

However I will agree with Mr. Bush in that each Latent Lab should have a copy on its library shelf. Just digest it slowly.

Wow, thanks to you, too. . .I have a lot to look at now. . .

Julie

Hello All,

Sorry for jumping in late (as usual!). I have a few things to add from a chemistry perspective. Wow, the chemistry degree plus half-completed postgraduate degree in fingerprints really comes in handy sometimes!

1) Technically, over time it is possible that more amino acids are "released" and are available for reaction over time. This happens because there is protein (consisting of large chains of amino acids all linked together) present in the latent fingerprint deposit. This protein cannot react with ninhydrin directly as the amino acids are linked together (that is, the sites required to react are all taken up in the links binding together the amino acids). But if the protein somehow breaks down to release free amino acids, then it is possible for a reaction to occur. NOW, there is bacteria on the surface of the skin that can "cleave", or break down proteins in the fingerprint, and this may take a few days to occur - on this I am not sure as I am not a biologist. I'm not sure that this is the answer in the context of the problem at hand, but stay with me as I have an idea on how you can test this (see part 3)

2) The reaction you are carrying out with the steam press may not be as efficient as it could be.

Water is required for the reaction to progress, but don't forget that what we need for a fingerprint development is a very small amount of water since there is not much material in the fingerprint to react. So it is possible to put too much water onto the fingerprint, thereby washing away the water-soluble portion of the fingerprints. And amino acids are water-soluble so they can become either smudged or diffused into the paper, or washed away entirely.

This is why it is recommended in Australia to leave the sample overnight in a relatively humid environment after ninhydrin application, rather than heating.

In relation to the problem, it sounds as if there may be not enough water or ninhydrin getting to the system at the right time. It is possible that the steam is just evaporating off and not actually contacting with the fingerprint. This may particularly happen if you use other bits of paper to "sandwich" the sample between to protect it from the iron, it may be too thick to allow water to penetrate through. You might find that this happens with inherently dry fingerprints (or older fingerprints that have evaporated to an extent) as there is not enough water in the fingerprint itself to promote the reaction.

Also, how do you apply the ninhydrin - is it by spraying or by immersion? Try immersing if you spray, or try immersing for a bit longer (try 30 seconds) to allow greater contact time.

3) To test these theories:

If you can find some amino acid in the lab somewhere (glycine, alanine, ornithine or serine is good as these are the most abundant found in hand secretions). Make a dilute solution (0.001M or so), spot this onto a piece of paper a few times (maybe 5 or 10 microlitres), allow to dry, then apply ninhydrin and the press. If it does not develop immediately, then you know that point (1) is not the case, and you need to look at (2). If it does develop immediately, then you know that point (2) is not the case, and point (1) you can explore in more detail with a microbiologist.

4) We also have noticed that some fingerprints will react even without heat treatment under the right conditions, and some will not react no matter what you do to it. This is because of the difference in the amount of material secreted or transferred by the donor. Those donors with more amino acids in the fingerprint will give you a more intense, and quicker reaction than those that do not secrete or transfer as much. In chemistry we refer to that as "Le Chatelier's principle", and this is what we are trying to do by increasing the water or increasing the ninhydrin concentration. I can explain this more if you like later as I think I have an RSI from typing all this

I would love to hear debate on any flaws in my logic

Kind regards,
Shaheen

And after some sleep, I realise that scenario (1) would be more likely if the prints were untreated, but I would be interested to know if the bacteria would survive after ninhydrin treatment and 185 deg Celcius...?

Cheers,
Shaheen