Indiana University

New Instrumentation for Metallomics Studies

Gary M. Heiftje, Distinguished Professor, Robert & Marjorie Mann Chair,
Department of Chemistry

The Hieftje group at the Laboratory for Spectrochemistry of Indiana University has a number of activities underway in the field of metallomic analysis. Overall, the focus is on new instrumentation for optical and mass spectrometry, especially novel sources and spectrometer systems for metallomics. The sources are largely based on glow-discharge approaches, with some at reduced (conventional) pressure and others at atmospheric pressure. They offer new possibilities not only for sample fragmentation, atomization, excitation and ionization, but also for sampling. The spectrometers to be described are predominantly based on mass detection, but a method for imaging-based atomic-emission detection is also being evaluated.

One new source is intended for the simultaneous emission-based examination of spots on a two-dimensional (planar) chromatographic plate, such as one from thin-layer chromatography or two-dimensional gel electrophoresis. Coupled with a monochromatic imaging spectrometer designed in our laboratory, the glow-discharge source enables the simultaneous detection and quantification of spots that hold metal-containing proteins or those stained with silver, gold nanoparticles, or metal-containing affinity tags used to identify functional groups.

Another new source, also based on a glow discharge, samples metallic species directly from solution, and at atmospheric pressure. Similar to the “ELCAD” device described by others, this source offers a simplified design and outstanding detection limits. Fundamental characteristics of the discharge are also being studied.

A third glow discharge, also operated at atmospheric pressure, is intended for ionizing species directly from solid or gaseous samples for mass-spectrometric detection. This discharge strikes directly to the sampling cone of a time-of-flight mass spectrometer, is unusually stable, and can generate spectra that range in degree of fragmentation, from free atomic ions to clusters to molecular fragments, depending on the chosen operating conditions.

The final source for metallomics employs electrospray ionization (ESI). However, unlike other ESI sources, it can spray aqueous solutions directly, with no pneumatic assist, and into atmospheres ranging from air to helium. The latter feature promotes desolvation of the electrospray droplets because of the high thermal conductivity of helium.

One new sort of mass spectrometer is based on time-of-flight technology. Because of its speed, it can be coupled with switched or modulated ion sources, which can generate atomic, molecular, and fragmentation mass spectra on a time scale compatible with even the fastest chromatographic schemes. Further, when appropriately modified, it can be coupled to two or more ion sources at a time, to yield even more information about complex samples. The dual-source TOFMS has initially been coupled simultaneously to an ICP and to an ESI source, the first to produce elemental mass spectra and the second to be used for speciation and metallomic information.

The second form of mass spectrometer is based on a sector-field arrangement. However, it is fitted with a simultaneous-recording 128-channel detector array, so a broad range of molecular fragments, elements and isotopes can be measured at once, and continuously. Its sensitivity exceeds that of quadrupole mass filters, and its isotope-ratio performance rivals that of thermal-ionization mass spectrometry. To illustrate the ability of the new instrument to measure mass spectra simultaneously and rapidly, it has been coupled to transient atomization sources, including laser ablation and electrothermal vaporization.
 

email: Hieftje@indiana.edu

URL: http://www.indiana.edu/~gmhlab/