Jason Beckert of Microtrace to present at annual MAFS meeting in St. Paul, MN

Beckert, J. (2014) Investigation of Latent Polarization in a UV-Vis Microspectrophotometer: Practical Lessons and Unexpected Phenomena. Midwestern Academy of Forensic Scientists Annual Meeting (St. Paul, MN).

Presented on: 10/6/2014

Microspectrophotometry (MSP) is a common instrumental technique used in criminalistics laboratories around the world.  Typically employed during the analyses of fibers and paint, it has found a place in trace evidence laboratories for decades.  The scientific foundation upon which it is based is well-established in the literature, and the basic principles of absorption and transmission are easy to grasp.  While seemingly simple, the collection and interpretation of high quality MSP data is not necessarily a trivial task, as it requires the user to be both a competent microscopist and spectroscopist.

This presentation will discuss our laboratory’s investigation of potential latent (i.e., unintentional) polarization in one of our UV-Vis MSP instruments.  Latent polarization, if present, is a concern to forensic scientists because it can cause errors during the comparison of known and questioned samples if it is not accounted for.

Initially believed to be a straightforward task, our preliminary data revealed unexpected factors at work including: illumination source (tungsten halogen vs. xenon), slide composition (glass vs. quartz), the effects of tilted coverslips, and polarizer instability.  Attempts to understand these unforeseen variables prompted the exploration of new experimental avenues.

The conclusion of this presentation will focus on the practical lessons learned during the ensuing research and the answer to our initial question: is there latent polarization in our instrument?


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