Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
Requests for drug analysis accounted for nearly half of all requests (DNA, toxicology, latent prints, etc.) submitted to forensic laboratories in the United States (Storm et al., 2010). A study by RTI International found that laboratories are only capable of processing about 80% of their controlled substances requests. Based upon this statistic, an estimated 220,000 cases per year would be back-logged. Therefore, tools that can improve the process of seized drug analysis would be of use. This project addresses one such concept, the use of retention indices as a means to improve drug screening using gas chromatography/mass spectrometry (GC/MS).;When drugs that co-elute (such as methamphetamine and phentermine) are analyzed, a mass spectrum would not be useful as both substances will give similar spectra. This presents problems especially with designer drugs that are similar in structure and molecular weight. Retention index, when coupled with mass spectrometry, can differentiate drugs that co-elute, thus reducing false positives and improving screening processes and the reliability of identification of compounds with similar mass spectra.;To date, retention indices have been listed as single whole numbers by providers such as the DEA and NIST. A survey of data obtained from different sources show that is often in disagreement between sources for the same compound on the same column. This is not unexpected, but does indicate the need for determination of a realistic range (i.e., uncertainty) that should accompany any reported retention index. In the case of similar compounds, this is not just desirable, it is essential. The goal of this project was to examine factors that could contribute to uncertainty (different instruments, different days, etc.), evaluate the relative importance of these factors, and to suggest defensible methods for incorporating uncertainty into retention index values.;This study used a DB-5 equivalent column (5% phenyl 95% methylpolysiloxane stationary phase) to find the uncertainty range between two different manufactures of gas chromatographs and manufacturers of columns. It was determined that a thinner film afforded the best repeatability of RI within the same instrument when concentrations were in the parts-per-million range. It was also determined that with the same experimental parameters and stationary phase but varying film thickness, the RI values could not be combined between instruments. The RI values from the thicker film produced a slightly larger uncertainty range compared to the thinner film. However, RI could be used to identify the components of a mixture that co-elute with poor resolution of peaks. RI has the potential to reduce false positives and decrease the backlog of drug analysis requests in forensic laboratories. However, for a universal library, the experimental parameters would have to be standardized on the most common columns used in drug analysis (DB-1 and DB-5 equivalents).
Cadau, Amanda M., "Reproducibility of Retention Indices Examining Column Type" (2013). Graduate Theses, Dissertations, and Problem Reports. 440.