Abstract
Bulk cash smuggling is a serious issue in recent years. It is estimated that $6–36B flow illegally between the United States and Mexico each year during otherwise legitimate border crossings. A nondestructive bulk currency detection system (BCDS) for screening pedestrians, vehicles and shipping containers will significantly improve boarder security, protect domestic economics and deter criminal and terrorist activity. However, such a practical device is not yet available because neither the target detection technique nor the instrumentation has been defined. In this paper, we evaluated the currency characteristics that provide a basis for detection, relevant physical/chemical instrumental approaches, and a rationale for selection of an approach to build a practical BCDS. US currency releases volatile compounds. These emissions can be used as a chemical signature in currency detection. The literature regarding characterization of volatile compounds associated with US currency is limited. To identify the unique vapor signature of US currency, we analyzed VOC emission from currency bills using thermal desorption GC/MS. This enabled calculation of emission rates of volatile compounds. The results were consistent with prior studies of currency emissions. From our data and the literature, a tentative fingerprint that represents currency can be selected from among the complex background present in real currency. The analysis shows that a most-likely US currency vapor signature contains a specific set of volatiles at low concentrations. A successful practical BCDS based on volatiles must be able to accurately identify and quantify a speciated set of trace chemicals from a complex and highly variable matrix. Variations of GC/MS with SPME preconcentration can result in near-term methods. Future developments are needed to address optimization of methodology and meet the need for rapid sampling, detection with speciation. Sensor arrays can also provide a platform for currency detection and would improve logistics over larger instruments.
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