Research: New Ideas and Instrumentation, Fundamental Plasma Studies, Molecular Analysis and Chemical Sensors, Elemental Mass Spectrometry

Mattauch-Herzog Geometry Mass Spectrograph

Development of Plasma Source Time-of-Flight Mass Spectrometry

Gradient Dilution Flow Injection Analysis for the Study of ICP Matrix Effects

Elemental Mass Spectrometry through the Use of Hydride Generation

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The Mattauch-Herzog geometry mass spectrograph (MHMS) has been coupled to several conventional ionization sources, such as the ICP and glow discharge. Recently, molecular analyses have been achieved with the Mattauch-Herzog geometry mass spectrograph (MHMS) through the use of the flowing atmospheric-pressure afterglow (FAPA)  ionization source. This combination marks the first detection of molecular species with the MHMS-FPC system (see Array Detector Atomic Mass Spectrometry). With the FAPA source, molecules are directly desorbed and ionized from solid surfaces. Furthermore, negative ions can be easily created when electronegative species, such as nitro groups from various explosives, are present. The MHMS-FPC system is easily converted to negative ion mode by inverting all ion optic potentials and the magnetic field. No changes are necessary to the FPC. Active ingredients from pharmaceutical tablets and explosive standards have been analyzed with the negative ion FAPA-MHMS-FPC system.

Development of Plasma Source Time-of-Flight Mass Spectrometry

In contrast to scan-based mass analyzers, time-of-flight mass spectrometers (TOFMS) are capable of simultaneous multi-elemental analysis. Since all masses are extracted instantaneously from a plasma, greater measurement precision is gained through ratioing techniques. Because no slits are utilized, high transmission efficiency can result in enhanced sensitivity for ultra-trace analyses. The limited mass range of atomic analyses (0-250 amu) allows production of complete atomic spectra at a rate exceeding 20 kHz. This high spectral generation rate makes TOFMS an excellent tool for transient samples (e.g. chromatography, laser ablation), reducing temporal and quantitative errors. Continued refinement of ion optical systems including collision cells, quadratic ion extraction systems and hybrid reflectrons will further enhance performance.

Laser ablation (LA) uses the intense power of a tightly focused pulse of light to remove microscopic quantities of material from solid samples for elemental analysis. Direct interrogation of a sample's surface reduces sample preparation and the likelihood of contamination. When combined with inductively coupled plasma mass spectrometry (ICP-MS), LA-ICP-MS is a powerful technique that offers high sensitivity and broad dynamic range for most elements in the periodic table. Additionally, because the ablating laser can be focused to a very small spot size, LA can provide highly spatially resolved elemental information. Because of its high speed, TOFMS is a nearly ideal approach for use with LA-ICP-MS. A new technique, termed standardless semiquantative analysis, has been developed to obtain concentration information from samples without the need for tedious calibration procedures.

Since arsenic exposure can have adverse health effects, determination of these species is very important. Hydride generation is routinely employed to determine arsenic-containing species to remove matrix interferences. Only species that form volatile hydrides are sampled, so most of the sample matrix is removed. In our laboratory, a gas sampling glow discharge (GSGD) source can be sustained with a wide variety of working gases (helium, argon, hydrogen, and neon). The GSGD is used to atomize and ionize the arsine produced by the hydride-generation reaction, and these ions are then detected with time-of-flight mass spectrometry (TOFMS). The ratios of the hydride species (As+, AsH+, AsH2+ and AsH3+) give an indication of the robustness of the discharge.