Superglue II

From Chempedia

FINGERPRINTS - VISUALIZING THE INVISIBLE

Authors: Beth Rich, Mike Ritchie, Anthony Rupp, and Merrily Sadlovsky

Introduction

A critical component of any criminal investigation is the detection and analysis of fingerprints left at a crime scene. Crime scene investigators typically photograph the visible fingerprints and compare them to the prints in an automated fingerprint identification system. The invisible, or latent, prints prove more challenging and require additional processing in order to examine and identify them. A common technique employed by crime lab technicians to develop latent prints on nonporous surfaces is the superglue fuming method.

The superglue fuming method, also called cyanoacrylate fuming, involves heating the liquid superglue to the point of vaporization (54-56 degrees Celsius) in a closed compartment that contains the item featuring the invisible fingerprints[1]. Once the superglue vapors interact with the fingerprint residue, which is composed primarily of water and organic and inorganic compounds such as fatty acids, sugars, amino acids, sodium, potassium, calcium, and chloride[2], it forms a visible, hard, white substance on the ridges of the print. At this point, the crime lab technician can photograph and analyze the print.

The superglue fuming method for capturing fingerprints was first developed and used by the Criminal Identification Division of the Japanese National Police Agency in 1978.[3]Not long after, the United States Army Criminal Investigation and the Bureau of Alcohol, Tobacco, and Firearms labs started using the superglue fuming method. Today, federal, state, and local criminal justice organizations frequently use this technique.


Chemistry behind the Superglue Fuming Method

The superglue fuming method utilizes superglue’s unique chemical properties. Superglue is an adhesive with extraordinary bonding capabilities - just a few drops of the clear liquid and you can permanently glue almost anything together! Superglue was invented accidentally by Dr. Harry Coover in 1942.[4] During World War II, Dr. Coover and colleagues were trying to find a way to use clear plastic to make gun sights for soldiers out of chemicals known as cyanoacrylates. Unfortunately, at the time, Dr. Coover and associates found the cyanoacrylates "too sticky" to work with and discounted them.[5] However, in 1951, while working for Kodak, Dr. Coover and a group of chemists were using cyanoacrylates to develop heat-resistant polymers for jet plane canopies. It was at this time that Dr. Coover identified the cyanoacrylate’s bonding ability. Dr. Coover and Kodak patented the discovery, refined it, and marketed it to the public as superglue.

The active ingredient in superglue is ethyl 2-cyanoacrylate (C6H7NO2) or methyl 2-cyanoacrylate (C5H5NO2)[6] (a.k.a. cyanoacrylates), depending on the superglue brand/type. Cyanoacrylates are covalently bonded molecules called monomers.


Image:Superglue_1.gif

Figure 1. Ethyl 2-cyanoacrylate monomer (Reference 6)

Image:Superglue_1.gif

Figure 2. Methyl 2-cyanoacrylate monomer (Reference 6)


When the liquid superglue is heated to the point of vaporization (54-56 degrees Celsius), the cyanoacrylate molecule vapors interact with a weak base to begin the anionic chain polymerization reaction.[7] In the superglue fuming method, the anionic chain polymerization reaction is initiated by H2O, which acts as a weak base by donating an electron pair to a cyanoacrylate monomer.[8]


Image:Superglue_3.gif

Figure 3. Anionic Polymerization Reaction (Reference 7)


The CH2group is very electropositive due to the electron-withdrawing properties of the cyanide and ester groups.[9] As a result, the electron pair from the H2O are attracted to this region. This attraction changes the carbon-carbon double bond to create bonding sites on both ends of the cyanoacrylate monomer. As the electron pair is passed on, each monomer changes the next one to create the bonding sites on both ends of the cyanoacrylate monomers in a chain-like fashion.[10] Bonds are created between the cyanoacrylate monomers, and the monomers form long repeating chains of monomers called polymers. These polymer chains form the hardened visible white substance on the ridges of the latent fingerprints. The superglue fuming method is a time consuming process and can take anywhere from one to five hours depending on the condition of the fingerprint, the chemical composition of the superglue, and the amount of humidity in the container.[11] However, maintaining the humidity in the container at 80% and keeping the air in the container constantly circulated accelerates the process.[12]


Safety Issues

Once the fingerprints have finished processing, the superglue fumes must be vented out of the container by high-powered fans. Superglue fumes are considered an irritant to the eyes, respiratory system, and any other exposed mucous membranes.[13] Superglue vapors are also flammable and its combustion can produce dangerous and potentially lethal amounts of cyanide gas. Therefore, caution must always be exercised when working with superglue fumes.


Conclusion

Despite the safety concerns associated with the superglue fuming method, it is an often-used tool of many crime scene lab technicians. It allows police agencies to gather fingerprint evidence where twenty years ago there would have been none. It is an extremely important technique in forensic science that has helped convict many current inmates, while exonerating a number of innocent citizens.


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Footnotes

  1. ^ Methyl 2-Cyanoacrylate (MCA) and Ethyl 2-Cyanoacrylate (ECA). U.S. Department of Labor. Occupational Safety and Health Administration website. http://www.osha-slc.gov/dts/sltc/methods/organic/org055/org055.html (accessed September 27, 2005).
  2. ^ Rowe, Walter F. Forensic Chemistry. Kirk-Othmer Encyclopedia of Chemical Technology. 2004.
  3. ^ Dixon, K.; Wu, J.: Brennan, R.W.; Goldsmith, P. Development of a Finger Printing Device on a Mobile Robot. J. of Forensic Sci. 2004. 49(2), 290-299.
  4. ^ Massachusetts Institute of Technology Lemelson MIT Program website http://web.mit.edu/invent/iow/coover.html (accessed October 17, 2005).
  5. ^ Massachusetts Institute of Technology Lemelson MIT Program website http://web.mit.edu/invent/iow/coover.html (accessed October 17, 2005).
  6. ^ International Programme of Chemical Safety. Concise International Chemical Assessment Document 36: Methyl Cyanoacrylate and Ethyl Cyanoacrylate. http://www.inchem.org/documents/cicads/cicads/cicad36.htm (accessed September 23, 2005).
  7. ^ University of Rochester Department of Chemistry. Introduction to Polymer Chemistry. http://www.chem.rochester.edu/~chem421/anionic.htm. (accessed November 5, 2005).
  8. ^ Brubaker, C. (2 June 2000). The Chemistry of Superglue. http://voh.chem.ucla.edu/vohtar/spring00/30H/pdf/Brubaker.pdf (accessed November 5, 2005).
  9. ^ Brubaker, C. (2 June 2000). The Chemistry of Superglue. http://voh.chem.ucla.edu/vohtar/spring00/30H/pdf/Brubaker.pdf (accessed November 5, 2005).
  10. ^ Brubaker, C. (2 June 2000). The Chemistry of Superglue. http://voh.chem.ucla.edu/vohtar/spring00/30H/pdf/Brubaker.pdf (accessed November 5, 2005).
  11. ^ Brown, E.W. The Cyanoacrylate Fuming Method. 1990. http://www.ccs.neu.edu/home/feneric/cyanoacrylate.html (accessed September 23, 2005).
  12. ^ www.chemsoc.org (accessed September 23, 2005).
  13. ^ Dixon, K.; Wu, J.: Brennan, R.W.; Goldsmith, P. Development of a Finger Printing Device on a Mobile Robot. J. of Forensic Sci. 2004. 49(2), 290-299.
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