Ivan Miller and Dr. Daniel Austin, Chemistry and Biochemistry
Mass spectrometry has been a common analytical procedure for over fifty years. Today it is most commonly used to characterize and quantify unknown solutions, solids, and vapors in chemical and biochemical environments by determining the specific masses of atoms and molecules. Ion traps have become standard methods in analysis as they have dramatically improved the selectivity and resolution of mass spectrometers. Ion traps use applied voltages to create electrical fields in a small trapping volume. These fields interact with the molecules in the mass analyzer by trapping ionized molecules over a broad mass range. The trapped ions are eventually ejected towards the detector by descending or ascending mass and subsequently detected and characterized.
Dr. Daniel Austin has developed a novel design to make a new ion trap called the planar ion trap. The ion trap has been constructed and recent simulations have shown that it has several advantages. It is much smaller than the conventional ion trap and it allows for easy adjustment of the electric field in order to change selectivity. It also increases the sample size that can be analyzed and it improves resolution.
The planar ion trap is constructed by placing concentric rings on two opposing plates. The electrical field is created by applying a voltage potential to each individual ring. Thus any electric field can be created and changed by simply altering the potentials applied to the rings. This trap is also a much more geometrically simple object allowing for easy machining and alignment.
During this past winter, spring, and summer semesters I worked with Dr. Austin in developing the novel ion trap for mass spectrometry. The trap was fabricated by micro fabrication and assembled in a vacuum chamber. We began by testing relatively light weight chemicals such as dichloromethane, but initial trials showed no observable signal. Subsequently, we explored different aspects of the project in hopes of finding a correctable flaw. We found that the trap was somehow shorting to ground. However, thorough searches yielded no obvious electrical shorts. We decided to rewire the instrument with precise insulation. The grounding problem seemed to be solved, but a new, not entirely unrelated, problem appeared. Once the trap was well-insulated we found a signal that only mimicked the energy source for the trapping field. To eliminate or at least minimize the feedback we focused on precision electrical shielding along with insulation. At last the problems were fixed but still no signals were detected.
We next investigated our ion source and found that the electron gun was highly inefficient. Without effective ion generation we were certainly not going to trap any ions. The electron gun was prepared in the laboratory and several shortcuts were made in its production. To eliminate several of any possible problems we decided to opt for a more conventional electron gun provided by Dr. Lee’s company, Torian©. While replacing the ion source we also reconstructed the vacuum chamber in order to accommodate a more open and accessible environment for the ion trap and testing equipment.
To our great satisfaction we were finally able to detect a signal, but the signal was not as good as we had hoped. It showed successful ion generation but showed no evidence of ion trapping or selective ejecting. We attempted to find additional instrument flaws and decided that a complete new trap design and simplification was in the project’s best interest. We decided that starting more basic and adding complexity would be more successful than the current approach. Subsequently, the trap was refabricated with fewer concentric rings and therefore fewer electrical contacts. We also constructed a valve manifold that would allow us to easily control sample injection and helium purging.
Recently, and to our great pleasure, we have been able to record spectra, showing both successful ion generation and ion trapping. Unfortunately, we have not been able to calibrate the instrument or identify the ions. I presented our work at the 22nd Annual Spring Research Conference for the College of Physical and Mathematical Sciences in March of 2008, for which I received an outstanding presentation award and recognition. A recent article was also published on this project detailing our research and results.1 I have recently graduated and have begun working for a pharmaceutical company in New York, but work on the project is continued by a doctoral student and the recent addition of a post doctoral student.
I consider the experience I gained from this research to be invaluable. The close personal relationship I was able to develop with Dr. Austin afforded many additional opportunities and a close friendship that I hope to maintain throughout my life. I also developed critical reasoning and problem solving skills that have proven valuable in my new career. Further search is required for this project to be finished but I am proud and thankful that I was able to play a significant role in its infant stage and be an author on a published paper.
- Novel Ion Traps Using Planar Resistive Electrodes: Implications for Miniaturized Mass Analyzers, Daniel E. Austin, Ying Peng, Brett J. Hansen, Ivan W. Miller, Alan L. Rockwood, Aaron R. Hawkins, and Samuel E. Tolley Journal of the American Society for Mass Spectrometry doi:10.1016/j.jasms.2008.03.019, (2008).