FOSexample2 - Mass Spectrometry (MS) Mass spectrometry (MS)...

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1 Mass spectrometry (MS) is different from other spectrometry methods. Most spectrometry methods are based on interaction of electromagnetic radiation or another form of energy with molecule. A spectrum is created during absorption or when molecules are in the ground state again. Mass spectrometry however, ionizes molecules and the ions are then resolved due to their mass-to-charge ratio (m/z) when electrostatic fields are applied to them (Nielsen, 2003). In MS one wants to find the molecular mass of a sample and this is found from a mass spectrum. The spectrum reveals how many isotopes of a given element are in the material, and then this provides the structural information on the compound. Mass Spectrometry (MS) A Background The earliest mass spectrometry dates back to the early 1900s when J. J Thomson invited Francis William Aston to be his student at Cambridge. Thomson was the first person to use MS for analysis of both solids and gases and made MS useful in different areas of science. Thomson encouraged Aston to develop better mass analyzers (with higher resolution); Aston soon began building mass spectrographs (which are similar to spectrometers). Then, the MS with higher resolution soon provided proof for the existence of isotopes of many of the chemical elements and recorded their molecular mass (Downard, 2007). This information eventually led to the development of even better mass spectrometers and resulted in more knowledge to determine the structural information on compounds. At first, spectrometry devices were called mass spectrographs because the instruments recorded the spectrum of the mass values on a photographic plate (De Laeter, 2008). Today’s method is similar, but instead of having the spectrum showing on a plate, it electronically converts to a reading of relative abundance versus mass/charge ratio. The different MS methods have the following common features (see figure 1): a sample introduction system, a method of creating ions from neutral sample molecules (ion source), a means of separating the charges and determining their mass-to-charge ratios (mass analyzer), and an ion detector which can also quantitize the number of ions (Baldwin, 2005). The main goal in MS is to separate charged molecules based on molecular mass and isotopes, and to detect and identify the unknown. Figure 1 Parts that are in all MS
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2 Thomson was the first person to analyze solids by MS. One of the factors why solids can be analyzed by MS today is that the ion source charges the liquid compounds. This charge also makes the liquids more similar to gases and thus easier to analyze by the mass spectrometer. Also, the ion source is responsible for ionization of molecules which can be read from the mass spectra. The ion sources that are mostly used today are electrospray ionization (ESI) and Matrix- Assisted-Laser-Desorption/Ionization (MALDI) (see figure 2). The main difference between them is that ESI is mostly used as a liquid, while the molecules for MALDI have to be in a dried or solid
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This note was uploaded on 03/03/2011 for the course FOS 4311 taught by Professor Kristinsson during the Spring '08 term at University of Florida.

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FOSexample2 - Mass Spectrometry (MS) Mass spectrometry (MS)...

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