Spectroscopy and Chemometrics for Cultural Heritage and Forensics: Conservation of Magnetic Tape by Identifying Degraded Polymer Signatures; and Characterizing the Chemiluminescent Reaction of Luminol with Blood
Date of Award
Open Access Dissertation
Chemistry and Biochemistry
Stephen L. Morgan
The first half of this manuscript focuses on the identification of degraded magnetic tape using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and multivariate statistics. For several decades before the digital era, magnetic tape was the dominant audio and visual recording medium. A majority of magnetic tapes contain polyester urethane (PEU) binders, which are known to degrade via hydrolysis, making the retrieval of recorded data difficult and at times impossible. Degraded tapes are currently identified through visual inspection followed by playback on vintage equipment. However, if degraded tapes are played, they are likely to stick and shed onto player guides and heads, resulting in irreversible data-loss. A total of 133 quarter-inch audio tapes were analyzed by ATR-FTIR. Classification of IR spectra in regards to tape playability was accomplished using principal component analysis (PCA) followed by quadratic discriminant analysis (QDA) and K-means cluster analysis. The first principal component suggests intensities at the following wavenumbers to be representative of non-playable tapes: 1730 cm−1, 1700 cm−1, 1255 cm−1, and 1140 cm−1. QDA and cluster analysis both successfully identified 93.78% of non-playable tapes in the calibration set and 92.31% of non-playable tapes in the test set. This application of IR spectra assessed with multivariate statistical analysis offers a path to greatly improve efficiency of audio tape preservation. The second half of this manuscript addresses the wide range of reported detection limits of the forensic luminol test for bloodstains. Luminol (3-aminophthalhydrazide) has been used for blood-stain detection by forensic investigators for over 60 years. When a luminol solution is sprayed onto areas suspected of containing blood, it reacts with the heme moiety of hemoglobin to give a faint bluish-white chemiluminescense. Absolute and relative sensitivities of different luminol formulations have been studied for decades. The range of published luminol detection limits for bloodstains spans nearly five orders of magnitude from 100× to more than 5,000,000× dilute bloodstains. We identify several factors that could affect the response of luminol to dried bloodstains and control them. We obtain a luminol detection limit of ~200,000× diluted blood as an estimate of the best case detection limit. The outcome of this work is a standardized method for measuring the chemiluminescent intensity emitted from the reaction of bloodstains with luminol.
Cassidy, B. M.(2015). Spectroscopy and Chemometrics for Cultural Heritage and Forensics: Conservation of Magnetic Tape by Identifying Degraded Polymer Signatures; and Characterizing the Chemiluminescent Reaction of Luminol with Blood. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/3257