The Construction and Optimization on an Ion Mobility Spectrometer for the Analysis of Explosives and Drugs

Today, over 15,000 Ion Mobility Spectrometry (IMS) analyzers are employed at worldwide security checkpoints to detect explosives and illicit drugs. Current portal IMS instruments and other electronic nose technologies detect explosives and drugs by analyzing samples containing the headspace air and loose particles residing on a surface. Canines can outperform these systems at sampling and detecting the low vapor pressure explosives and drugs, such as RDX, PETN, cocaine, and MDMA, because these biological detectors target the volatile signature compounds available in the headspace rather than the non-volatile parent compounds of explosives and drugs. In this dissertation research volatile signature compounds available in the headspace over explosive and drug samples were detected using SPME as a headspace sampling tool coupled to an IMS analyzer. A Genetic Algorithm (GA) technique was developed to optimize the operating conditions of a commercial IMS (GE Itemizer 2), leading to the successful detection of plastic explosives (Detasheet, Semtex H, and C-4) and illicit drugs (cocaine, MDMA, and marijuana). Short sampling times (between 10 sec to 5 min) were adequate to extract and preconcentrate sufficient analytes (> 20 ng) representing the volatile signatures in the headspace of a 15 mL glass vial or a quart-sized can containing ≤ 1 g of the bulk explosive or drug. Furthermore, a research grade IMS with flexibility for changing operating conditions and physical configurations was designed and fabricated to accommodate future research into different analytes or physical configurations. The design and construction of the FIU-IMS were facilitated by computer modeling and simulation of ion’s behavior within an IMS. The simulation method developed uses SIMION/SDS and was evaluated with experimental data collected using a commercial IMS (PCP Phemto Chem 110). The FIU-IMS instrument has comparable performance to the GE Itemizer 2 (average resolving power of 14, resolution of 3 between two drugs and two explosives, and LODs range from 0.7 to 9 ng). The results from this dissertation further advance the concept of targeting volatile components to presumptively detect the presence of concealed bulk explosives and drugs by SPME-IMS, and the new FIU-IMS provides a flexible platform for future IMS research projects.

The economic well -being of low -income immigrants in the U.S.: An examination of the impact of the 1996 welfare reform on immigrants

The 1996 welfare reform, for the first time in U.S. history, set a five-year residence requirement for immigrants to be eligible for federal welfare benefits. This dissertation assessed the impact of the 1996 welfare reform, specifically the immigrant provisions, on the economic well-being of low-income immigrants. This dissertation also explored the roles that migration selection theory and social capital theory play in the economic well-being of low-income immigrants. ^ This dissertation was based on an analysis of the March 1995, March 2002, and March 2006 Annual Demographic Supplement Files of the Current Population Survey (CPS). Both logistic regression and multiple regression were used to analyze economic well-being, comparing low-income immigrants with low-income citizens. Economic well-being was measured in the current survey year and the year before on the following variables: employment status, full-time status (35 or more hours per week), the number of weeks worked, and the total annual wage or salary.^ The major findings reported in this dissertation were that low-income immigrants had advantages over low-income citizens in the labor market. This may be due to immigrants' stronger motivation to obtain success, consistent with migration selection theory. Also, this research suggested that immigrant provisions had not ameliorated employment outcomes of low-income immigrants as policymakers may have expected.^ The study also confirmed the role of social capital in advancing the economic well-being of qualified immigrants. Ultimately, this dissertation contributed to our understanding of low-income immigrants in the U.S. The study questioned the claim that immigrants are attracted to the U.S. by welfare benefits. This dissertation suggested that immigrants come to the U.S., to a large extent, to pursue the goal of upward mobility. Consequently, immigrants may employ greater initiative and work harder than native-born Americans.^