Fundamental Guidelines of Mass Spectroscopy - Essay Example

Mass Spectroscopy Mass spectroscopy, also called mass spectrometry, is an analytical technique performed in the laboratory to divide constituents of a given sample according to their mass. Basically, in this technique, a substance is subjected to electromagnetic forces that have sufficient energy to fragment the molecule. The positive components that result from this electron bombardment are then accelerated into a vacuum through a magnetic field. It is in this magnetic field that the components are eventually sorted on the basis of mass to charge ratio. Because a majority of the ions produced in the mass spectrometers are positively charged, they are cations; these ions tend to carry an overall unit positive charge. Consequently, the ratio of mass to charge abbreviated as m/e becomes the equivalence of the molecular weight of the component. In this technique, the analysis of the data generated involves the re-assembling of the components and then moving backwards to find the original sample molecule (Klein 673). The fundamental guidelines of mass spectroscopy date back to as early as the 1890s when J.J Thomson was able to ascertain the mass to charge ratio of the electron. Additionally, Wien who illustrated that the magnetic deflection of anode (negatively charged terminal) rays were positively charged is a founding figure in mass spectroscopy. These men were honored with Nobel Prizes for their experiments in this technique. In later years, probably in 1912, J.J. Thomson again was in the limelight yet with another study on Neon atom. In his study, he subjected the Neon-20 atom to mass spectrometry and found a variant atom, Neon-22. This suggested that neon in fact was an isotopic element. The earliest form of a mass spectrometry machine was built in 1918 by A.J. Dempster. It was until the mid 1960s that the method of mass spectrometry came into proper and common use because the machines were reliable and affordable (Pavia 443). With the advancement in ionization techniques of high molecular weight substances between 1980s and 1990s, this analytic procedure has grown immensely. Introduction of affordable instruments that provide high resolution has enabled researchers in all fields to conduct in depth analysis of various molecules ranging from oligonucleotides, and other biological compounds. Mass spectrometry traverses all fields and has been of significant value in drug development, and drug discovery. Within the health sector, this technique has been vital in the testing of blood and urine samples for detection of compounds termed as markers in specific conditions. Environmentally, this technique has been relied on for monitoring water and air quality as well as testing of energy reserves (Pavia 449). The procedural breakdown of mass spectroscopy begins when a very low concentration of sample molecule is allowed to pass through an ionization chamber. The chamber is usually maintained at very high levels of vacuum. Within this chamber, the sample substance is subjected to a high energy electron beam that essentially produces negatively charged ions. As a result of this bombardment, the constituent molecules in the sample substance fragment. The positively charged ions that are produced are the passed on to an analyzing tube. The path which these cations flow within the tube is curved as result of a magnetic field. Positively charged particles, cations which have the lowest rates of motion implying a low mass, are deflected most by the strong magnetic field. These molecules subsequently collide with the walls of the analyzer. On the other hand, high molecular weight components which tend to have high momentum are not deflected by the magnetic forces and as such do not undergo collision. Of importance are the ions which possess proper mass to charge proportion (Klein 687). Notably, these ions flow through the path of the analyzer, leave the path through an outlet and run into the collector. This collision with the collector produces an electric current which is stepped up and eventually detected. However, the strength of the magnetic field can be varied or adjusted to produce a variance in the mass to charge ratio. The end result of this whole process depicts a plot of comparative intensity against the mass to charge ratio. The most intense crest within the spectrum is called the base peak and the remaining peaks are reported in comparison to the base peak intensity. These peaks are most often depicted as sharp and are represented by vertical lines. The splinter process of the sample molecules follows a simple and calculated chemical pathway of the constituent ions (Klein 679). These ions that are formed reflect the most stable cations and radical cations that are all positively charged particles from which the molecule is synthesized. The highest molecular weight crest within the chemical spectrum represents the parent molecule without an electron. It is usually called the molecular ion. In some cases, small peaks can be distinguishable in the spectrum and, when they occur at higher levels than the molecular ion, they depict isotopic forms. A majority of the molecules especially unstable protons do not show base peaks in their spectra. This is a common phenomenon with alcohols (Pavia 455). There are various methods of mass spectrometry through which substances can be analyzed. One common method is electron ionization whereby, the sample molecule is converted to ions. In Electron Ionization-Mass Spectrometry (EI-MS), a ray of high energy electrons is emitted from a filament heated at high temperatures. The high intensity beam of electrons strikes the molecule and in the process, the resultant outcome of the collision is loss of electron form the molecule. A cation, positively charged particle is formed which is then carried by a repeller plate and directs it to the accelerator. Potential difference then carried the cation into one or more outlets through a uniform beam. This is then detected after subjection into a magnetic field. The method has the advantages of being robust and also because of the inexpensive hardware. Additionally, there is significant splintering of the molecule into a pattern that is reproducible (Klein 683). Another variant in mass spectrometry is chemical ionization. In CI-MS the sample molecules are introduced in combination with a stream of ionized gaseous substance which is in excess compared to the sample. During the collision process with the preionized reagent, some of the molecules in the sample are ionized through mechanisms of electron or proton transfer or even adduct formation. Examples of ionizing reagents used in chemical mass spectrometry include methane, methanol and isobutene (Pavia 449). An important form of mass spectrometry is desorption ionization techniques that includes SIMS, FAB and MALDI. In contrast to chemical and electron ionization methods which require relatively volatile molecules, desorption techniques allows for analysis of bulky non-volatile substances. The sample in analysis is diffused in a matrix and placed in a path of high energy beam of ions. The disparities in the three modes come in the type of ions subjected to the sample. In Secondary ion mass spectrometry (SIMS), the beam of ions is positively charged elements such as Ar+ and Cs+. In fast atom bombardment (FAB), the beams of ions that strike the sample substance are neutral ions of Xenon and Silver. Lastly, the beam of ions that strike the molecule in matrix-assisted laser desorption ionization (MALDI), is usually high intensity photons. MALDI method uses nitrogen emitter but in some cases, the filament is modified to emit infra red. The knockdown of the sample molecules by the high intensity radiation ionizes part of the samples and ejects them from the medium. The resultant charged molecules are then accelerated to an analyzer. Other ionization techniques include electronspray and thermospray ionization. These techniques are beneficial in the study of high molecular weight biomolecules as well as other non volatile and unstable compounds (Klein 689). Eugenol Formula: C10H12O2 Molecular weight: 164.2011 Eugenol Spectrum Eugenol is a compound primarily associated with odor and taste in cloves. The two most intense crests in the mass spectrum depicted above are due to Molecular ion whose mass to charge ration is at 164. The other peak is the one occurring at amass to charge ratio of 149, this one is M – 15 and is positively charged. A rather less intense peak on the spectrum is a fragment ion at 137. This is as a result of 27 electrons from the base peak at 164. Since this compound does not have Nitrogen atoms, this loss cannot be as a result of HCN (Smith 187). In conclusion, mass spectrometers take advantage of the fact that different molecules and chemical substances have different mass to charge ratios. As a result, it is possible to divide molecules on the basis of their mass to electric charge relative amount. Generally, a mass spectrum is a representation of the measure of cations of specific mass to charge proportion. Peaks within the spectrum are a relative measure to the quantity of ions of each mass. Therefore, mass spectrometry plays a vital role in the determination of chemical and physical properties of various molecules. This technique allows for determination of the relative atomic mass, molecular weight and the chemical structures of different chemical compounds (Klein 675). Briefly, the process of analysis in mass spectrometry is a six step one beginning with sample vaporization. The vaporized sample is then ionized in a high vacuum chamber full of electron beams. The ions are the accelerated through a path of an electric field. Ions pass through a magnetic field perpendicular to the electric potential according to their mass-charge ratios. Ions with apposite mass to charge quotient are collected. However, different ions can be collected upon variation in the electric or magnetic field strengths. Eventually, the detector recognizes the weight of each cation or radical cation from its path. The output is displayed as a mass spectrum showing different peaks (Pavia 457). Works Cited Klein, David R. Organic Chemistry. New Jersey: John Wiley and Sons, 2011. Print. Pavia, Donald L. Introduction to Spectroscopy. Stamford: Cengage Learning, 2009. Print. Smith, Martin R. Understanding Mass Spectra: A Basic Approach. New Jersey: John Wiley and Sons, 2004. Print. Read More