Robert S. Brown
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B.S., 1978, University of Massachusetts, Lowell
Ph.D., 1983, Virginia Tech
Postdoctoral, 1983-87, University of California, Riverside
Our research is primarily centered in the general area of mass spectrometry. Current research efforts include the study of fundamental ionization processes; the development of new or improved mass spectrometry instrumentation and the application of mass spectrometry to large biomolecules and atmospheric aerosols. For non-volatile samples, our primary analysis technique involves the use of high-powered pulsed lasers (laser desorption, both with or without a matrix) to effect ionization of a wide range of molecule classes. Biologically relevant molecules such as proteins, peptides and glycoproteins and synthetic commercial polymers typically are studied using matrix-assisted laser desorption/ionization (MALDI). Smaller molecular weight and environmentally important aerosols are being analyzed using a DART (Direct Analysis in Real Time) ionization source. We are also exploring the incorporation of pulsed laser ablation of less volatile/larger molecular weight samples directly into the DART source (laser assisted DART). Mass analysis is carried out via either time-of-flight (TOF) or quadrupolar ion trap (Thermo Finnigan LCQ) mass spectrometers. Both of these mass spectrometers are well suited for pulsed laser ionization sources. The LCQ mass spectrometer allows atmospheric pressure ionization sources to be utilized and also offers multistage (MS/MS) analysis capabilities. TOF mass spectrometers combine very high sensitivities (routine femtomole range) with an extended mass range for analyte analysis.
A long-standing area of interest in our laboratory is the study of the underlying ionization mechanism in MALDI. The specific mechanism for the matrix assisted laser desorption/ionization (MALDI) process remains in completely understood. Recent work in our laboratory has involved synthesis of novel cinnamic acids as matrices to both explore aspects of the underlying MALDI process and to develop improved matrices compatible with longer wavelength (355 nm) lasers that are becoming more commonly employed for MALDI. Additionally, we continue to study IR-MALDI (using mid-infrared lasers rather than the more common UV lasers) in order to gain additional insights into the MALDI ionization mechanism and are exploring potential new application areas. Also, pulsed IR lasers (such as carbon dioxide and mid-IR OPOs) are being used for laser ablation combined with DART post-ionization of lower volatile/thermally labile analytes. A particular application of laser-assisted DART that we are currently exploring involves the characterization of atmospheric aerosols produced during the winter inversion periods here in Cache Valley, Utah that have been collected on glass filters. The aim of these studies is to better understand the underlying chemical processes involved the formation of these aerosols, which degrade wintertime visibility and are potentially a major health concern.