Detecting toxic chemicals in air using miniature mass spectrometers

Jonell N Smith, Purdue University

Abstract

There is an increasing need for chemical instrumentation that can be utilized in situ for homeland and transportation security, industrial hygiene, monitoring of chemical spills, industrial process control, environmental monitoring, and facility air monitoring. Mass spectrometers offer a powerful combination of speed, sensitivity, generality, and high information content. Used in combination with various ionization techniques and sample introduction systems, miniaturized instrumentation offers advanced solutions to chemical measurement problems in the areas of interest. The analytical capabilities of both home-built and commercially available miniature ion trap mass spectrometers equipped with electron ionization as well as several types of sample introduction systems were investigated. With the appropriate sampling method, the instrument was used to rapidly detect, identify, and quantitate a wide range of compounds including toxic industrial compounds and chemical warfare agent simulants, with high accuracy, chemical selectivity, sensitivity to trace amounts of analytes, and low false positive rates. The miniature mass spectrometers discussed have mass ranges up to about m/z 500, unit resolution, tandem mass spectrometry capabilities, and limits of detection in the low to sub-parts per billion range. In-trap ion/molecule reaction experiments were needed to analyze the low mass compound ammonia by reacting it with an analyte of higher mass to create a product ion that was above the low-mass cutoff of the miniature mass spectrometer (∼ m/z 40). Source parameters of the ambient ionization method of desorption electrospray ionization – a method which allows for rapid, direct analysis of chemical analytes from untreated surfaces – were also investigated using a bench-top, commercially available, mass spectrometer. In summary, it is shown that an automated, fieldable, miniature mass spectrometer can be used for facility air monitoring. Compounds that fall below the instrument’s lowmass cutoff can be detected using ion/molecule reactions. Glow discharge electron ionization is a powerful, reliable, robust alternative to filament ionization. Miniature mass spectrometers equipped with electron ionization sources have been used with various sample introduction systems to detect toxic chemicals in air in the sub-parts per billion range.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Atmospheric Chemistry|Analytical chemistry|Surgery

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