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MCAT

Unit 3: Lesson 1

Chemical and physical sciences practice passage questions

Mass spectrometry in the operating room

Problem

One technique used to differentiate between cancerous and normal tissue is running samples through a mass spectrometer. Chemists have discovered that the ratios of certain lipids from cell membranes can uniquely identify various biological tissues, including tumors. A library of lipid spectrometer signatures can be gathered and referenced to determine if a tissue has cancer cells or not, but such techniques require special preparation as spectroscopy requires ionized particles for analysis.
Chemists recently have found however, that the smoke produced from electrosurgical knives happens to be comprised of the exact type of ionized particles needed for mass spectrometry. These ionized particles move through the spectrometer past a magnetic field, and depending on the charge of the particles, and the direction of the field, this magnetic field would cause a semi-circular deflection of the ionized particles’ path. The radius of this deflection is directly dependent on the m/z ratio, which is the ratio of a particles mass to its charge. Thus, simply by analyzing smoke as surgeons remove a tumor, a mass spectrometer can identify whether or not the cut tissue matches a profile of cancer, which can inform the surgeon whether or not an incision is adequate for the accurate removal of cancer.
Figure 1. Charged particle with velocity V passing through magnetic field B
Citation: Sci Transl Med 17 July 2013: Intraoperative Tissue Identification Using Rapid Evaporative Ionization Mass Spectrometry Júlia Balog, László Sasi-Szabó, James Kinross, Matthew R. Lewis, Laura J. Muirhead,Kirill Veselkov, Reza Mirnezami, Balázs Dezső, László Damjanovich, Ara Darzi,Jeremy K. Nicholson and Zoltán Takáts Vol. 5, Issue 194, p. 194ra93
As seen in Figure 1, a positively ionized particle with velocity V enters a magnetic field moving right, with the field going into the screen. Given this arrangement, what direction would the particle initially deflect toward as it moves through the field?
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