Putting a New Spin on FT-MS

Courtesy of Thermo Finnigan Mass spectrometers that combine the high resolution and mass accuracy of Fourier transform mass spectrometry (FT-MS) with the ion storage and separation capabilities of quadrupole-quadrupole (Q-q) and linear ion trap mass spectrometry were recently introduced by Bruker Daltonics of Billerica, Mass., and Thermo Finnigan of San Jose, Calif. These instruments could accelerate the pace of protein identification in the rapidly expanding field of proteomics. FT-MS is based on ion cyclotron resonance (ICR), in which ions generated by electrospray ionization or other methods are stored in an ICR cell in the presence of a magnetic field. The stored ions are excited with a radio frequency (RF) pulse, resulting in a cyclical motion with a frequency inversely proportional to the ions' mass-to-charge (m/z) ratio. The excited ions generate an image current that is then detected. Since each ion has a different frequency, the detected signal is a collection of the frequency components from each of the ions in the sample. A Fourier transform is used to tease out the individual frequencies and produce the mass spectrum. The mass-resolving power of FT-MS is directly proportional to detection time and magnetic strength. The Bruker and Thermo Finnigan systems feature superconducting magnets with strengths of up to 12 Tesla and 7 Tesla, respectively, and offer mass accuracies of less than 1 part per million, which is nearly an order of magnitude better than the most advanced time-of-flight-based mass spectrometers currently available. But Bruker Daltonics' APEX-Q system and Thermo Finnigan's LTQ-FT system extend the capabilities of FT-MS by coupling it to either a Q-q or a linear ion trap interface. Both technologies serve as ion storage or preparation methods, allowing the user to dissect proteins of interest from complex mixtures prior to FT-MS analysis, or to selectively accumulate ions and thus enhance sensitivity for low-abundance proteins. These capabilities increase the throughput of the instruments, giving them the speed required for proteomics applications, explains Helmut Muenster, marketing manager, organic and FTMS, Thermo Finnigan. GREATER ACCURACY, BETTER IDs Michael Gross, director of the Washington University Center for Biomedical and Bioorganic Mass Spectrometry, says that, while the capacity for accurate mass measurement by FT-MS has existed for more than two decades, the ability to control how many charged particles are present in an ICR cell at a given time has not. By controlling the number of ions introduced into the detector, users can improve mass accuracy by minimizing the space-charge effect, which arises from electrostatic repulsion between like charges. Improved mass accuracy, in turn, provides more efficient database searching and more reliable protein identification. "If you can make these measurements more and more accurately, you can find that mass becomes distinctive; [it] discriminates one protein from another by discriminating one peptide from another. And it becomes another parameter that you can incorporate in the search ... a mass that's accurate to a part per million or maybe even less," says Gross. Thermo Finnigan's system is slated for availability in August or September, according to Muenster; versions of Bruker Daltonics' APEX-Q are currently in use at the Mayo Clinic and Pacific Northwest National Laboratory, both of which collaborated with Bruker Daltonics in the development of the technology. David Muddiman, professor of biochemistry and molecular biology, Mayo Medical School, is collaborating with Bruker in the development of software for a 12-Tesla FT-ICR instrument that Muddiman plans to use for biomarker discovery and reverse immunogenetics, or the development of synthetic vaccines that target biological weapons. Muddiman explains that hybrid FT-MS instruments like the APEX-Q are the only means to deal with highly complex mixtures like blood serum or urine on a time scale suitable for clinical applications. "We can actually take blood serum and look at hundreds or over a thousand proteins in the course of a day, where other mass spectrometry platforms, like time-of-flight, require on the order of a week or so to look at the same sample at the same level of detail," he notes Victor Fursey, director of sales and marketing, Bruker Daltonics, says the hybrid FT-MS systems can also be used for top-down approaches to protein identification in which mass spectrometry is used to directly sequence intact proteins, rather than peptide fragments. "[The system] is designed to give you a simple approach, with fewer enzymatic steps, to look at intact proteins without any chemical manipulation or modifications," he explains. --Aileen Constans function sendData() { document.frm.pathName.value = location.pathname; result = false if (document.frm.score[0].checked) result = true; if (document.frm.score[1].checked) result = true; if (document.frm.score[2].checked) result = true; if (document.frm.score[3].checked) result = true; if (document.frm.score[4].checked) result = true; if (!result) alert("Please select") return result; } .myradio{background-color : #94bee5} Please indicate on a 1 - 5 scale how strongly you would recommend this article to your colleagues? Not recommended 1 2 3 4 5 Highly recommended Please register your vote

Putting a New Spin on FT-MS

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