Mass Spectroscopy Quiz Questions Correctly Answered

Mass Spectroscopy Quiz Questions Why is the GC so commonly used in cooperation with a Mass Spectrometer? - ✔ ✔ These two components, used together, allow a much finer degree of substance identification tha n either unit used separately. It is not possible to make an accurate identification of a particular molecule by gas chromatography or mass spectroscopy alone.Sometimes two different molecules can also have a similar pattern of ionized fragments in a mass spectrometer (mass spectrum). Combining the two processes reduces the possibility of error, as it is extremely unlikely that two different molecules will behave in the same way in both a gas chromatograph and a mass spectrometer. Therefore, when an identif ying mass spectrum appears at a characteristic retention time in a GC -MS analysis, it typically lends to increased certainty that the analyte of interest is in the sample. What are the three basic steps in Mass Spectrometry? - ✔ ✔ Creation, Separation, and Detection of Ions Why are the analyte molecules ionized? And how is this done? - ✔ ✔ The molecules are analyzed in order to accelerate in an electric field and separate according to mass to charge ratio (m/z). When a small quantity sample is inject and v aporized under high vacuum, the sample is then hit with electrons of 25 -80 eV causing the valence electron to be "punched" off of the molecule, forming an ion. How are the daughter ions or fragments formed in Mass Spectrometry? - ✔ ✔ Excess energy in the ionization chamber causes bonds to break forming fragments. Why are these fragments helpful in identifying and species? - ✔ ✔ The complexity and reproducibility of these fragmenting patterns is vital to identifying a compound. What happens to a fragment whi ch touches the side of the spectrometer? - ✔ ✔ The fragment neutralizes and is sucked up by the vacuum and doesn't get identified. How are the ions accelerated in the Mass Spectrometer? - ✔ ✔ Ions are repelled from the source by placing a potential between the repeller and the focusing slits. The positive ions are accelerated by electron field • Ions with a lower mass/charge ratio move faster What function do the focusing slits perform? - ✔ ✔ Help to direct and accelerate the ions to the mass analyzer What problems might we see if we increase the energy of the electron beam? And if we reduce the energy of the electron beam? - ✔ ✔ The more ionization energy applied, the more fragments may occur. If the IE is reduced, fewer ions may be formed as well as f ewer fragments. How are the daughter ions or fragments formed in Mass Spectroscopy? - ✔ ✔ Produced by some sort of fragmentation of a larger ion Why are these fragments helpful in identifying and species? - ✔ ✔ The method for identifying the fragment ions make use of the difference between the m/z value of a given fragment ion and that of the molecular ion Electron Ionization often produces spectra which are referred to as a fingerprint for the compound. Why is this true? Provide some detail. - ✔ ✔ The resu lting fragmentation ion pattern in the mass spectrum represents a more or less specific fingerprint of the analysed molecule. Thus compounds can often be identified using mass spectrometric libraries. How does a magnet work to separate fragments? - ✔ ✔ The magnet aids in the removal of ion fragments that are too heavy and too light by bending their path toward the wall of the deflection chamber which neutralizes the particles causing them to be removed by vacuum. What is the purpose of the quadrupole? - ✔ ✔ Quadrupole Mass Filter is the most common method of separating ions. Why does the positive potential superimposed with an AC current allow high mass particles to pass through the quadrupole? Explain in great detail with a figure or two. Refer to the video links. - ✔ ✔ As the positively charged ions move through the chamber between the two positively charged metal roles, their direct path would to be move straight through due the the repulsion of both positive charges. However, since the two positive rods a ct as a high mass filter and filters out ions less than a certain amount in mass, as negative AC current is applied causing a momentary negative charge which attracts the ions. The smaller is mass ions are faster to transition (attract), causing them to ev entually hit the wall of the chamber and be removed, whereas the larger mass ions are more lethargic causing them to attract more slowly to the momentary negative attraction, allowing them to weave their way through. Why does the negative potential superim posed with an AC current allow Low mass particles to pass through the quadrupole? Again an explanation and figure would be required here. - ✔ ✔ Since the positively charged particles would simply attract towards the negative rods, a positive AC current wou ld be applied allowing for the rods to become momentarily positive, thus repulsing the particles. When the rods change charges, the smaller ions are more able to change paths quickly, allowing them to weave through. However, when larger particles change pa ths, the are slower causing them to move closer and closer toward the rods and are neutralized. How does the quadrupole filter all but a single m/z? - ✔ ✔ Certain RF (radio frequency) voltages are applied to the metal rods. The DC and RF voltages are varie d depending on the particular m/z that is