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Final Report Summary - ACID (Analytical Chemistry Instrumentation Development)

The chemical analysis of vapors is an area of great industrial and scientific interest. For example, there is an increasing interest in the development of non-invasive diagnostic tests based upon the analysis of exhaled breath; or there is an increasing need to rapidly screen for explosives and drugs within freight containers with high sensitivity, selectivity, accuracy and precision. These applications require new instrumentation that at present do not exists. The overarching objective of this project has been to develop technologies that address the stringent analytical requirements needed to optimally perform in such scenarios. In particular, the main objective of this project has been to develop novel instrumentation for the characterization of gas-phase analytes with high sensitivity and in real-time. In order to meet this goal, we have undertaken the following tasks:
1. We have designed a new architecture for Secondary Electrospray Ionization (SESI) sources intended for the analysis of gaseous samples. The engineering development has included detailed numerical simulations to optimize the source geometry in order to maximize ionization efficiency and ion transmission into the mass spectrometer (MS). The agreement between numerical simulations and experimental results was very good. This highly sensitive ion source has been designed to be easily interfaced with several atmospheric pressure ionization-mass spectrometers (API-MS) manufactured by a variety of major MS companies. In this way, standard API-MS instruments, which in their original commercial configuration are not intended for the analysis of gases, could be upgraded into sensitive real-time, vapor sniffers.
2. A second major development has been the optimization of a Differential Mobility Analyzer (DMA), which is a product developed by SEADM. This device is at the core of their explosives detection platform. We have improved its already impressive performance by reducing the entry of neutral vapors and droplets into the classification region. As a result, we have improved the resolution of our mobility spectra, as we may now prevent the clustering of neutral vapors with ionic species of interest. In addition, we have developed a radical new solution to overcome this problem: the use of an atmospheric pressure photo-ionization (APPI) source, as an alternative to SESI. A second generation APPI prototype has also been developed with a refined design that is suitable for commercialization.
3. A major limitation to improving the sensitivity of real-time analysis using SESI is that the mechanisms by which neutral vapors are ionized were poorly understood. To address this fundamental problem, we have investigated in detail the ionization mechanisms of SESI using deuterated gaseous species. We have concluded that gas-phase ion-molecule reactions are the governing process, allowing us to rationally select operating parameters in order to maximize target vapor detection.
4. Finally, we have benchmarked the instrumentation developed during this project. We have showcased the potential of the ACID project devices in various fields. We have demonstrated the potential of this set of novel analytical tools through the following applications:
o We have shown that the SESI sources developed during this project are suitable for performing real-time analysis of exhaled air, with unprecedented sensitivity, while detecting metabolites that have never before been detected. This breath analysis platform is currently being used in clinical trials to diagnose a range of respiratory diseases, potentially opening new opportunities to develop novel diagnostic tests.
o We have also shown that SESI is suitable for monitoring the metabolism of yeast with a level of performance that was not even anticipated. This study has revealed a large number of metabolites produced by yeast from glucose that are neither reported in the literature, nor are their biochemical origins deciphered. With the technique demonstrated here, researchers interested in focused disciplines such as yeast physiology and food quality analysis will gain new insights into the biochemical capability of this simple eukaryote.
o Similarly, plant volatiles were analyzed continuously over two consecutive days, opening new opportunities to understand plant chemical communication in vivo. This new tool may ultimately assist in the improvement of crop yields and plant defense from pests. Along the same lines, the SESI-MS system has been used to monitor volatiles emitted during grape ripening, which is of great importance for the wine industry.
o The APPI source has shown great potential to detect, with high sensitivity, many species that may be difficult to ionize by SESI, such as polychlorinated dioxins and furans. This analytical tool has been shown to efficiently detect persistent environmental pollutants in real samples collected within the vicinity of industrial incinerators.
o The improved SESI-DMA-MS platform has been tested for the detection of explosives and has shown promise for detecting explosives nearly in real-time in challenging environments, such as freight containers.

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Life Sciences
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