Hi! I have two Ninhydrin questions for my fellow scientists out there. . .
1) I have come across a few cases now in which I have processed items with Ninhydrin, treated them with a steam iron, found nothing. . .then, a few days later, a beautiful latent developed - my question is, how long should evidence be held for examination after treatment with Ninhydrin to make sure that all latents have been developed? I used to treat evidence with a steam iron after Ninhydrin, if I found nothing, returned it to the Evidence Unit and moved on - but I'm finding that that probably is not a good idea and that I'm possibly missing some latents. Is a few days good enough, a week, what???? How prevalent is this phenomenon?
2) Also, I know that Ninydrin reacts to the amino acids in the latent print residue, and that amino acids are water soluable - so why then, does a steam iron (water) work (usually - see question 1 ) to catalyze the reaction and not "wash" the amino acids away? Just curious -
Question 1: Sometimes prints develop days after processing, even after acceleration with a steam iron. I have heard rumors of previously undeveloped prints showing up months or years later. I also have read or heard that sealing a document airtight in plastic after development helps preserve prints and might even help develop additional prints. In my lab, I seal ninhydrin-treated items in plastic ziplock baggies as soon as they dry after steaming, then tape over the seal to help ensure airtightness.
Actually, you can "steam away" prints. I have seen ninhydrin prints that get to much steam and the Ruhemann's Purple complex (that's NIN + AA) bleeds into the porous fibers and you lose some detail. Some agencies I have heard don't even steam the evidence b/c of potential loss of clarity from diluting/dissolving the RP. I think it depends, and for me, certainly the nature of the case and evidence, how "soft" a development technique that I will choose.
So definitely, if you use an iron, don't oversteam, too much steam can bleed out the detail and certainly may disrupt 3rd level detail.
(Come to think of it, this would make a good (and easy) comparative study if anyone is interested. Develop prints with and w/o steam and compare the clarity of the 3rd level detail, to see what % may be lost by steaming. Obviously a variable would be: (the amount of steam/unit time).
Glenn, I did that simple experiment years ago to show the potential disadvantages of a steam iron. Not only can the steam cause diffusion and paper fiber migration, but most "spit" small water deposits that can create serious problems. In addition, background discoloration starts to increase at temperatures above 80 C and increase disporportionately as the temperature is raised.
The sample was cut in two, and the proponents of the steam iron picked which half to use. Both halves were processed simultaneously in the same ninhydrin reagent for the same time. My post treatment was an ordinary lab oven set to 75 C using a silica slurry in the bottom for humidity. The steam iron was set at minimum temperature for steam passed over the other half approximately one inch above the surface (give or take - who has that steady a hand) at an even back and forth movement. The two halves were placed together upon visualization, and the oven processed half showed excellent third level. The steam iron processed half was suitable but did display third level loss. We have not used a steam iron since.
Many moons ago, my zoology professor explained to the class why so many experiments involve a 72 hour waiting period...Seems that is the length of time between getting the experiment set up on Friday, going home for the weekend, and checking it Monday afternoon. Very 'scientific'! I try to check development several times a day, and generally let everything 'bake' for about 2-3 days. I don't use a steamer anymore except to get the wrinkles out of my clothing. I currently use a microwave (up to two sheets in my little nuker, with a 1/2 cup of hot water, on high power for 2 minutes) to process my ninhydrined papers. My favorite method, although we no longer have them, was to just put the treated (not steamed) papers in a plastic bag and then lay them on top of my computer monitor (the older, big, fat ones, not the new skinny ones that don't give off heat). If I left the monitor on, it was the perfect temp to bake the prints and never overdevelop them.
I haven't done any steaming or heat-development in years. With the new HFE-2100 formula, the prints sometimes start developing before I can get my apron hung up. While I can start comparing the latent prints the same day, I usually wait for a day or two before making a more complete examination.
Like Pat mentioned, I, too, have had latent prints develop months later. Besides photographing the latent prints, I also make a copy of the paper on the copy machine and make notes on it. On one case, when I pulled the evidence about three months later when getting for court, I found several new latent prints had developed that were not present when I first make the copy of the page. I made the suspect several more times.
But, I have another question. When I used to use the old formula of Ninhydrin crystals in Methanol and Petroleum Ether, I could reprocess and sometimes get darker prints. I have had two cases with the HFE-2100 formula where the prints got worse on even disappeared when I reprocessed. Has this happened to others? I am certainly not comfortable about reprocessing anymore.
For those who want to leave their Nin treated items on the counter for several days I would recommend keeping track of the ambient humidity in the room. In our old lab we could leave treated items on the counter over the weekend and voila! purple prints on Monday morning.
Once we moved to our new lab these successes diminished. Later we started tracking the humidity--it was a constant 44% RH. It seems the new air conditioning system was very efficient, and worked against our efforts to develop these prints.
Now it is a constant 54% RH, still not optimal, but our Sanyo/Gallenkamp chamber takes care of the rest. I would be interested to find out if anyone has found prints that have deveoped long after processing with one of these chambers.
) to catalyze the reaction and not "wash" the amino acids away? Just curious -