On the other hand, also note that accidental contamination during sample preparation can mess up your results, and keeping a tab of these mass spec contaminants can help your experiment.
There are various ways of producing the required ions, and the method chosen depends on the nature of the sample molecule.
You can find out more information in the references below. Try out the technique and let us know what new applications it finds in your research. Has this helped you? Then please share with your network. I am very glad that you have provided interesting information about the detection of supra molecular compounds through mass spectroscopy.
Originally published February 16, Reviewed and republished June Facebook Twitter LinkedIn More. Written by Carl Saxton. As the effluents are in the liquid phase, this separation technique lends itself very well to being coupled with ICP-MS and ESI-MS methods, but is also found linked to ion trap and Orbitrap mass spectrometers too.
The principles and applications in clinical biochemistry has been reviewed by Pitt 19 and more recently Seger 20 , while applications in drug discovery have been reviewed by Korfmacher. Understanding the structure and organization of multiprotein complexes is critical to understanding cellular function.
Chemical crosslinking coupled with mass spectrometry XL-MS is a method that is complementary to structural biology techniques such as cryogenic electron microscopy cryo-EM and X-ray crystallography but provides lower-resolution structural information.
In XL-MS, a protein or protein complex is treated with a crosslinking reagent that introduces covalent linkages between specific functional groups in the protein. The crosslinked protein is then digested with an enzyme that breaks down the protein s and the resulting mixture is analyzed by LC-MS methods to identify crosslinked peptides and determine their sequences.
The locations of crosslinks provide structural information about the system under study. However, interpretation is complex as samples prepared in this manner contain far more unique chemical species than a digest of the non-crosslinked protein.
The number of potential crosslinked peptides increases quadratically with the sequence length. Nonetheless, XL-MS can be a useful tool to aid in the development of structural models for protein-protein interactions. The objective of hydrogen-exchange mass spectrometry HX-MS is similar to that of XL-MS — to study multiprotein complexes and in particular, protein structure and dynamics.
Advantages of HX-MS include the fact that it probes the structure of proteins in solution so crystallization is not necessary, it requires only tiny amounts of sample - 1, picomoles , it is amenable to studying proteins that are hard to purify and it can reveal changes in structure and dynamics over time.
HX-MS makes use of a chemical reaction whereby certain H atoms in proteins are in continuous exchange with the H atoms in solution. If an aqueous H 2 O solvent is replaced with heavy water D 2 O , then this exchange process can be followed. In particular, the H bonded to the amino acid backbone N atoms also referred to as the backbone amide H is useful for probing protein structure.
Once the exchange of H with D is complete, the sample can be analyzed by MS to provide information about protein structure changes with small molecule binding, protein folding or information about the structure of proteins that do not crystallize or are not amenable to other structural biology methods. Not only is MALDI-TOF an excellent method for MS analysis, it is also capable of generating images by step scanning the stage, continuously scanning the stage under repeated firing of the laser or by scanning the laser beam.
The resulting images can provide a wealth of information on, for example, large tissue sections, at a spatial resolution between m m. Since MALDI is a soft ionization technique, molecular information is retained and thus compounds of interest need not be tagged for detection, as in fluorescence microscopy. A typical mass spectrum is represented in Figure 2. Figure 2: The pentane mass spectrum. The strongest peak will therefore have a relative intensity of Pentane has the chemical formula C 5 H This is the molecular peak.
The entire molecule has been ionized in the source as a single entity without any fragmentation. But what of the other, stronger peaks? These are the result of fragmentation during the ionization process of pentane. With a bit of math, we can propose it might be C 4 H 9 , which would suggest one of the CH 3 groups was fragmented off during the ionization process, leaving the C 4 H 9 fragment molecular ion.
This is the equivalent of one of the CH 3 and CH 2 groups. These are due to extra Hs being stripped from the C 3 H 7 molecular ion during fragmentation. This forms the basis of interpreting mass spectra and requires a knowledge of not only the chemistry but also the structure of the parent molecule.
Clearly this could be a daunting task for all of the organic materials in existence. Fortunately, there are databases available that show mass spectra for many of these to assist interpretation. There is one more complicating factor that is more often observed in mass spectra from elements or small molecules. This is from the different isotopes from each element. In the pentane example we assumed that carbon has a mass of 12 amu. This is not strictly valid as carbon has 2 stable isotopes: one at mass 12 and the other at mass 13 the atom contains an extra neutron.
However, multiple isotopes of the same element can be useful. It is the basis of HX-MS described earlier, and also the basis for multi-isotope imaging mass spectrometry 26 , 27 where stable isotope are intentionally added to compounds and then isotope ratio images derived from the sample.
Those regions where the isotope ratio is greater than the natural abundance indicate the regions of the sample where the compound has been incorporated. Two common stable isotopes used to this effect are 13 C and 15 N. CCD Charge couple device. CE Capillary electrophoresis. CI Chemical ionization. DART Direct analysis in real time. DC Direct current. DESI Desorption electrospray ionization. EI Electron ionization. EM Electron multiplier. ESI Electrospray ionization. Mass spectrometers can be smaller than a coin, or they can fill very large rooms.
Although the various instrument types serve in vastly different applications, they nevertheless share certain operating fundamentals. The unit of measure has become the Dalton Da displacing other terms such as amu. Once employed strictly as qualitative devices-adjuncts in determining compound identity-mass spectrometers were once considered incapable of rigorous quantitation.
But in more recent times, they have proved themselves as both qualitative and quantitative instruments. A mass spectrometer can measure the mass of a molecule only after it converts the molecule to a gas-phase ion. To do so, it imparts an electrical charge to molecules and converts the resultant flux of electrically charged ions into a proportional electrical current that a data system then reads.
The data system converts the current to digital information, displaying it as a mass spectrum. Skip to main content. You are here Home » Science » Technology Areas.
What is Mass Spectrometry? The Ionization Source Molecules are converted to gas-phase ions so that they can be moved about and manipulated by external electric and magnetic fields. Example of a mass spectrum.
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