Mass spectroscopy

Mass spectroscopy

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  BY MADHUKAR 11GQ1R0028 Mass spectroscopy
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  INTRODUCTION  Massor molecular weight of a compound can be found in several ways .one such technique is using mass spectrometer  It is an analytical chemistry technique that helps identify the amount and type of chemicals present in a sample by measuring mass-to-charge ratio and abundance of gas-phase ions
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  Principle  Amass spectrometer generates multiple ions from the sample under investigation  This molecular ion undergoes fragmentation. Each primary product ion derived from the molecular ion, in turn, undergoes fragmentation, and so on.
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   The ionsare separated in the mass spectrometer according to their mass-to-charge ratio, and are detected in proportion to their abundance. A mass spectrum of the molecule is thus produced.  It displays the result in the form of a plot of ion abundance versus mass-to-charge ratio
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  Obtaining mass spectraconsist of 2 types;  Conversion of neutral molecule into a charged molecule, preferably to a positively charged molecule.  Separation of the positively charged fragments formed, based on their masses, by using electrical or magnetic field or both.
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  Instrumentation The instrumentconsists of three major components: Ion Source: For producing gaseous ions from the substance being studied. Analyzer: For resolving the ions into their characteristics mass components according to their mass-to-charge ratio. Detector System: For detecting the ions and recording the relative abundance of each of the resolved ionic species.
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  Components of aMass Spectrometer
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   In addition,a sample introduction system is necessary to admit the samples to be studied to the ion source while maintaining the high vacuum requirements (~10-6 to 10-8 mm of mercury) of the technique; and a computer is required to control the instrument, acquire and manipulate data, and compare spectra to reference libraries
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  With all theabove components, a mass spectrometer should always perform the following processes;  Separate these ions according to their mass-to-charge ratio in the mass analyzer.  Eventually, fragment the selected ions and analyze the fragments in a second analyzer.  Detect the ions emerging from the last analyzer and measure their abundance with the detector that converts the ions into electrical signals.  Process the signals from the detector that are transmitted to the computer and control the instrument using feedback.
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  Chromatographic techniques combinedwith mass spectrometry  An important enhancement to the mass resolving and mass determining capabilities of mass spectrometry is using it in tandem with chromatographic separation techniques.
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  Gas chromatography Acommon combination is gas chromatography-mass spectrometry (GC/MS or GC-MS). In this technique, a gas chromatograph is used to separate different compounds. This stream of separated compounds is fed online into the ion source, a metallic filament to which voltage is applied. This filament emits electrons which ionize the compounds.  The ions can then further fragment, yielding predictable patterns.  Intact ions and fragments pass into the mass spectrometer's analyzer and are eventually detected.
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  Liquid chromatography Indianapolis Museum of Art conservation scientist performing liquid chromatography– mass spectrometry.
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   Similar togas chromatography MS (GC/MS), liquid chromatography-mass spectrometry (LC/MS or LC-MS) separates compounds  chromatographically before they are introduced to the ion source and mass spectrometer. It differs from GC/MS in that the mobile phase is liquid, usually a mixture of water and organic solvents, instead of gas.  Most commonly, an electro spray ionization source is used in LC/MS. Other popular and commercially available LC/MS ion sources are atmospheric pressure chemical ionization and atmospheric pressure photo ionization.  There are also some newly developed ionization techniques like laser spray.
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  Applications Mass spectrometryhas both qualitative and quantitative uses. Structure of elucidation; Using nitrogen rule, peak matching, fragmentation pattern of a compound and % abundance of isotopes, structure of elucidation of organic compounds can be done. Detection of impurities; Impurities present can be detected by the additional peaks, highest value of mass peaks then compound itself, & from the fragmentation pattern
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  MS is nowin very common use in analytical laboratories that study physical, chemical, or biological properties of a great variety of compounds. As an analytical technique it possesses distinct advantages such as: Increased sensitivity over most other analytical techniques because the analyzer, as a mass-charge filter, reduces background interference Excellent specificity from characteristic fragmentation patterns to identify unknowns or confirm the presence of suspected compounds, Information about molecular weight.