Mass Spectrometry Flashcards
What is mass spectrometry used for and what machinery is used?
mass spectrometry is used to figure out the mass of a molecule which helps figure out the chemical formula. the gas chromatography mass spectrometer (gc-ms) is used by purifying molecules and then into the MS to help determine the mass
What is the main purpose of the MS?
it provides what the mass of a molecule is and the fragments that make it
the sample is injected into the sample source and the detector at the end helps us figure out the mass of particle
the heater heats up the sample really fast, vaporizes it before sending it into the electron collector. the vaporization turns the molecule from a liquid into a gas, which is necessary for the MS to work
What are the differences between NMR, IR, and MS?
NMR and IR use light (electromagnetic radiation)
MS does not use light
What does the electron collector do to the gaseous molecule? why is this important?
the molecule gets bombarded by electrons in the electron beam/collector that knocks off an electron (process is called electron impact ionization) creating a molecular ion (M+)
this is important because the detector at the end of the MS requires the molecule to be positively charged in order to detect the molecule
What does the detector do?
the detector keeps track of the mass to charge ratio (m/z)
the detector counts how many molecules are hitting the detector and figures out which one is hitting it the most, relative abundance. which ever molecular fragment is hitting the detector the most becomes 100% relative abundance and each other fragment follows
What is the importance of the magnet in the MS?
the magnet bends the molecular ions towards the detector. the amount of mass the molecule has determines the angle in which the magnet sends the M+, the smaller the mass, the greater the angle
Why are there many peaks in the MS graph?
the many peaks represent the different fragments of the molecule since removing an electron makes the molecule very unstable and fragments it
What is the base peak and the M+ number?
the base peak is the highest peak on the graph which is the most abundant fragment, the fragment with most relative abundance.
the M+ number is the molecular mass of the molecule, it is the small amount of hexane that did not fragment (M+ matches the molar mass)
What is the difference between the base peak and M+ peak?
the base peak is the highest peak on the graph and the M+ peak is the peak that represents the molecular mass of molecule. the base peak can be the M+ peak but it doesn’t happen often.
the smaller peak next to the M+ peak is called the M+1 peak
How are fragments formed and what are some common pathways?
fragments are formed by electrons being able to be ripped off from different places on the molecule put through the MS and going through the electron beam
some common ways are methyl, ethyl, propyl
What is the M+1 peak and why?
the M+1 peak is because of isotopic effects
What is chlorines relative abundance?
3:1
when you have a M+2 and a 3:1 ratio of the M+ and M+2, you will almost always have a chlorine
What is the Nitrogen Rule?
a compound containing an odd number of nitrogen atoms typically has an odd M+ and a compound containing an even number of nitrogen atoms, or no nitrogen atoms at all, typically has an even molecular mass
What are the two main types of fragmentation of alcohols?
alpha cleavage: cleaving off the alpha-beta bond forming a neutral radical that is not detected by the mass spec (because it is not positive)
dehydration: forms a water ion
Explain Amine and Carbonyl fragmentation.
amines also undergo alpha cleavage just like alcohols except you will typically see a M+ peak, which is more stable than alcohol
carbonyls generally undergo mclafferty rearrangement which form an alcohol with the C=O and a hydrogen
