By Julia Boguslavsky
May 9, 2003 | AFTER A TRANS-ATLANTIC journey, the U.K.-manufactured 12-Tesla magnet — the highest-power magnet used exclusively for biomedical research — finally arrived at its destination, the new Proteomics Research Center at the Mayo Clinic. To install the 1.5-meter-diameter, 3,700-kilogram magnet, Mayo had to cut a hole in the roof.
The product of a creative collaboration between the Mayo Clinic and Bruker Daltonics, this mammoth magnet will power the state-of-the-art Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS).
"The FT-ICR world is pretty small — there are only about 300 in the world," says David Muddiman, director of Mayo Clinic's W.M. Keck FT-ICR MS Laboratory. He confesses he finds the $2-million instrument "a little intimidating. You could probably buy four other high-end mass spectrometers instead, but will you be pushing the boundaries of molecular characterization?"
While conventional MS techniques measure molecular mass by colliding ions into a detector, FT-ICR MS traps ions in the ICR cell by magnetic and electric fields, forcing the ions to travel in circular orbits. The frequency of the ion cyclotron motion depends on the ion's mass-to-charge ratio. Since recording the image current produced by circulating ions is nondestructive, it may be repeated for multiple cycles. This improves the precision and confidence in mass assignment. Finally, applying a Fourier transform formula converts the frequency measurement into a mass measurement.
Magnetic resonance: The Mayo Clinic makes room for its new 3,700-kg, 12-Tesla magnet, which will power the Bruker Daltonics APEX-Q mass spectrometer.
"The key about FT-ICR is that it is by far the world's most powerful type of mass spectrometry for biological research," Muddiman says. "Its mass resolving power, mass accuracy, sensitivity, and dynamic range are unparalleled by other MS.
"With most MS, it's a give-and-take relationship. For example, if you increase sensitivity, you decrease resolving power. With FT-ICR, these properties are independent of each other. This is important in proteomics because we work with extremely complex mixtures that contain millions of peptides. We can't measure all of them without having all figures of merit on our side."
The mass accuracy, resolving power, and dynamic range of FT-ICR MS improves with higher magnetic field strength. High mass resolution is key in analyzing complex mixtures since it enables researchers to discriminate between very small mass differences and detect more "mass channels" in a single measurement. Increased dynamic range helps characterize rare proteins that have been subject to post-translation modifications and ensures consistent accuracy between samples of differing concentration.
A few weeks following the installation of the 12-Tesla magnet at Mayo Clinic, Bruker Daltonics officially launched the commercial version of the instrument, a hybrid Q-q-FTMS, at PittCon 2003. In development for more than two years, the APEX-Q is the combination of a tandem quadrupole (Q-q-) "front-end" and high-field FTMS. The APEX-Q comes in both 9.4- and 12-Tesla magnet configurations.
"APEX-Q represents a change in paradigm from the classical approach to FTMS," says Paul Speir, Bruker Daltonics' assistant vice president. "The hybrid instrument has the attributes of a triple-quad platform with FTMS-caliber performance. For the shotgun approach to proteomics, the APEX-Q offers mass-specific, automated LC-MS/MS — operating similarly to a triple-quad or Q-q-TOF system — with the added benefit of ultrahigh mass accuracy and resolution."
The Mayo Clinic instrument represents the highest-field commercially available FTMS system, the APEX-Q 12T. It allows Muddiman to routinely measure a half-million peptides for each sample, which becomes a necessity for proteomewide analysis of clinical samples.
Muddiman's lab profiles cells and biological fluids from human cancer (and control) samples to detect changes in protein abundance. The differentially expressed proteins are then identified either by searching peptide databases based on mass signatures or by sequencing.
"Most tandem MS can do that, but not for a million peptides," Muddiman points out. "We used to get a lot of data — and even some information — but most people looked at smaller genomes. To understand cancer, we have to look at mammalian proteomes, so the complexity increases."
Mayo uses the APEX-Q 12T instrument as a discovery platform to obtain "extremely comprehensive measurements of biological fluids and tissues. Once we identify the proteins of interest, we can use conventional tandem MS with isotope-labeled internal standards," Muddiman explains.
The ultimate goal is to identify ovarian and prostate cancer biomarkers and develop clinical diagnostics. "It's all about understanding cancer and patient care," Muddiman says.
Julia Boguslavsky is the conference director for Cambridge Healthtech Institute. She can be reached at email@example.com.