Mass-spectrometry

 

Essentially, mass-spectrometer consists of four units:  i.e. inflow system, ion source, magnetic focusing system and detector (fig.1).  In the inflow system the sample of the substance under analysis is evaporated in vacuum.  The produced vapors get into the ion source, where they undergo a bombardment by a bunch of accelerated electrons (the energy is usually of about dozens of electronvolt).  Irradiation energy is usually used to liberate electrons from the analyzed substance molecules – the latter being transformed into positively charged radical ions.  Such particles are highly reactive and unstable.  Here in the ionization chamber they undergo decay into charged and uncharged fragments (hence the method name "fission-fragment mass-spectrometry").  The whole ionization chamber is under high positive potential with respect to the other parts of the device.  Therefore, the electrostatic field expulses positive ions from the chamber.  Prior to leaving the chamber, the ion bunch goes through the system of electrostatic lenses and diaphragms, which results in narrow focused ion beam exiting the chamber, in which the ion speeds depend on their masses and charges.  

1 – Substance vapors; 2 – Ionization chamber; 3 – The m/e focused ions; 4 – Detector; 5 – Electron beam; 6 – Ion bunch; 7 – The detected part of an ion beam; 8 – Magnetic focusing zone

    Then the ion beam gets into the zone of magnetic focusing.  Here, in a magnetic field, the ion straight paths get curved, with the magnetic field geometry being calculated so as to focus the ions on the detector.  Finally ions approach the detector along individual paths, which are exclusively determined by the value of the ion mass–charge ratio (m/e). By varying an electrostatic or a magnetic field one can focus ion flows on the detector for every m/e value and quantitatively measure the ionic current corresponding to such particles, i. e. the value proportionate to the number of particles with the given m/e in the analyzed plasma.  The m/e sweep produces mass spectrum, in which m/e values are on X-axis, while the intensities of ionic current – or (which is the same) the share of particles with the given m/e in plasma – are on Y-axis.  As the produced fragments are predominantly monovalent, the m/e scale is practically the same as the scale of ionic masses.  
      In the described mass-spectrometry conditions (which are most common but far from singular) organic substances produce complex mass spectra.  However, one can distinguish in them most characteristic and intensive peaks corresponding to the main decay paths of the compound under consideration.  As the typical decay paths of many organic compounds classes, in particular monosaccharides, are now thoroughly studied, one can get a complete enough representation of the structure of a compound under consideration on the basis of a mass spectrum picture, having used minimum substance (less than a milligram, very often just micrograms) and spent minimum time (spectrum mapping with good equipment requires a few minutes).

There are other methods of analysis of nanomaterials:

• Ir-spectrometry
• X-ray structural analysis
• Spectrofotomery in ultra-violet and visible areas of the spectrum
• Highly effective solution chromatography
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