Improving the selectivity of fieldable mass spectrometry for analysis of targeted analytes in complex matrices
Abstract
Several methods were developed in order to facilitate in situ detection of organic compounds at trace levels in complex matrices. A ThermoFinnigan ITS-40 ion trap mass spectrometer was extensively modified to allow development of novel membrane interfaces. A single-sided MIMS (SS-MIMS) interface was developed which expands the utility of MIMS by performing adsorption and desorption of the analyte on the same side of the membrane. Data from this system have shown that polar, semi-volatile compounds can be detected at trace levels (low pptr) in air samples. A high surface area (12 cm2) counterflow (He sweep gas) MIMS system, has yielded semi-quantitative extraction of semi-volatile and volatile analytes from air matrices, with limits of detection in the low pptr range for many environmentally significant compounds. An external configuration of a trap-and-release MIMS has been developed and applied to detection of both volatile and semi-volatile inorganic chloramines. The method was shown to give temporal resolution of volatile vs. semivolatile compounds, which increases the sensitivity for semi-volatiles in the presence of volatiles. A MIMS system was designed and coupled to a miniature cylindrical ion trap based mass spectrometer, which was subsequently used for a field study of monochloramine in wastewater. Atmospheric pressure chemical ionization was employed for direct air analysis, without ion source modification, by using the sheath gas as the sample transport agent, allowing trace level detection of semi-volatile chemical warfare agent simulants in air. Ion chemistry was explored for a possible diagnostic reaction for the presence of nitroaromatic explosives. It was determined that substituted nitrobenzenes react with substituted benzonitrile radical cations in an ion trap mass spectrometer by a novel ion/molecule reaction involving NO2 elimination, forming an arylated nitrile, Ar 1+N≡CAr2 (where Ar1, Ar 2 = aryl).
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
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