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20 important questions on MS McMurry

What is mass spectrometry in simple words?

Mass spectrometry is a technique for measuring the mass, and therefore the molecular weight (MW) of a molecule. In addition, it's often possible to gain structural information about a molecule.

What are three main components of a mass spectrometry machine?

The three main components of a mass spectrometry machine are an
-ionization source (in which samples are given an electrical charge)
-mass analyzer (in which ions are separated by their mass-to-charge ratio
-detector (in which the separated ions are observed and counted)

What is cation radical and what does it have to do with mass spectrometry when it get his by the ionization source?

A cation radical is a molecule that has lost a valence electron, giving the molecule a positive charge and now has an odd number of electrons. When a ionization source, in this case a high-energy electron strikes an organic molecule, it dislodges a valence electron from the molecule

What happens to molecule in a mass spectrometer when it gets bombarded by electrons?

When a molecule gets bombarded by electrons it transfers so much energy that most of the cation radicals fragment after formation. They break apart into smaller pieces, some of which retain the positive charge and some of which are neutral. The fragments then flow through a curved pipe in strong magnetic field, which deflects them into different paths according to their mass-to-charge ratio (m/z). Positively charged fragments are sorted by the mass spectrometer onto a detector, which records them as peaks at the various m/z ratios.

What happens to neutral fragments in the pipe of the mass spectrometry?

Neutral fragments in the pipe with a strong magnetic field are not deflected by the magnetic field are lost on the walls of the pipe

What does amu stand for, and what is the limit amu a spectrometer can detect?

Amu stands for atomic mass units and a spectrometer can detect masses up to approximately 2500 atomic units

What is the mechanism behind the common type of mass spectrometer called the quadrople mass analyzer?

In he quadrupole mass analyzer a set of four solid rods is arranged parallel to the direction of the ion beam. An oscillating electrostatic field is generated in the space between rods. For a given field, only one m/z value will make it through the quadrople region - the others will crash into the quadrople rods or the walls of the instruments and never reach the detector

What is on the x-axis and the y-axis when the mass spectrum of a compound is typically presented as a bar graph?

When the mass spectrum of a compound is presented as a bar graph on the x axis is usually the the masses (the m/z values) and on the y axis the intensity, or relative abundance of ions of a given m/z striking the detector

What is the meaning of terms base peak and parent peak in the mass spectrum bar graph?

Base peak in the mass spectrum bar graph is the tallest peak assigned an intensity of 100%
Parent peak in the mass spectrum bar graph is the peak that corresponds to the unfragmented cation radical. Parent peak is also called the molecular ion M+

Why does not every compound show a molecular ion in its electron impact mass spectrum and how can this be prevented?

Not every compound shows a molecular ion in its electron impact mass spectrum because some compounds cause some compounds fragment so easily that no molecular ion in observed. In such cases alternative 'soft" ionization methods that do not use electron bombardment can prevent or minimize fragmentation

What is M+1 peak in a bar graph of the mass spectrum of a particular molecule?

M+1 peak in a bar graph of the mass spectrum of a certain molecule means is a peak that appears one mass unit higher than molecular ion because the molecule contain a naturally occurring heavier isotope such as 13C and 2H

How do alcohols undergo fragmentation in a mass spectrometer and how does that show up in the mass spectrum?

Alcohols undergo fragmentation in a mass spectrometer by two pathways; alpha cleavage and dehydration. In the alfa-cleavage pathway, a C-C bond nearest the hydroxyl group is broken, yielding a neutral radical plus a resonance-stabilized, oxygen containing cation
In the dehydration pathway water is eliminated

What is the nitrogen rule in mass spectrometry?

The nitrogen rule in mass spectrometry says that a compound with an odd number of nitrogen atoms has an odd-numbered molecular weight. An even-numbered molecular ion usually means that a compound has either zero or an even number of nitrogen atoms

When do ketones and aldehydes undergo the McLafferty rearrangement?

Ketones and aldehydes undergo the McLafferty rearrangement when they they have a hydrogen on a carbon three atoms away from the carbonyl group. Then they undergo the characteristic mass-spectral cleavage called the McLafferty rearrangement

What is another alpha cleavage ketones and aldehydes frequently undergo in a mass spectrometer?

Another alpha cleavage ketons and aldehydes frequently undergo in a mass spectrometer is an alpha cleavage of the bond between the carbonyl group and the neighboring carbon. Alpha cleavage then yields a neutral radical and a resonance stabilized acyl cation

What is the formula for kinetic energy in the TOF mass spectrometry?

The formula for kinetic energy in TOF mass spectrometry is;

What is the principle behind the TOF (time-of-flight) mass analyzer which are linked to both MALDI (matrix-assisted laser desorption ionization) and ESI (electrospray ionization)

The principle behind the TOF analyzer is that ion are accelerated by a voltage and ions with different m/z values travel a different speeds. Lighter molecules move faster, and heavier molecules move slower

What is the drift tube in a TOF mass analyzer?

The drift tube in a TOF mass analyzer is the long/tube flight region through which the ions travel after being accelerated/charged, as they move at different velocities and take different amounts of time to complete their flight

What is another unit biochemist use in mass spectrometry instead of amu?

Another unit biochemist use in mass spectrometry instead of amu is dalton, abbreviated Da. 1 dalton = 1 amu

What is the beer lambert law and how can it be interpreted?

The Beer-Lambert law describes how much light a substance absorbs according to its concentration and and the path length of light through the sample

The question on the page originate from the summary of the following study material:

Analytical methods in organic chemistry

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MS McMurry

20 important questions on MS McMurry

What is mass spectrometry in simple words?

What are three main components of a mass spectrometry machine?

What is cation radical and what does it have to do with mass spectrometry when it get his by the ionization source?

What happens to molecule in a mass spectrometer when it gets bombarded by electrons?

What happens to neutral fragments in the pipe of the mass spectrometry?

What does amu stand for, and what is the limit amu a spectrometer can detect?

What is the mechanism behind the common type of mass spectrometer called the quadrople mass analyzer?

What is on the x-axis and the y-axis when the mass spectrum of a compound is typically presented as a bar graph?

What is the meaning of terms base peak and parent peak in the mass spectrum bar graph?

Why does not every compound show a molecular ion in its electron impact mass spectrum and how can this be prevented?

What is M+1 peak in a bar graph of the mass spectrum of a particular molecule?

How do alcohols undergo fragmentation in a mass spectrometer and how does that show up in the mass spectrum?

What is the nitrogen rule in mass spectrometry?

When do ketones and aldehydes undergo the McLafferty rearrangement?

What is another alpha cleavage ketones and aldehydes frequently undergo in a mass spectrometer?

What is the formula for kinetic energy in the TOF mass spectrometry?

What is the principle behind the TOF (time-of-flight) mass analyzer which are linked to both MALDI (matrix-assisted laser desorption ionization) and ESI (electrospray ionization)

What is the drift tube in a TOF mass analyzer?

What is another unit biochemist use in mass spectrometry instead of amu?

What is the beer lambert law and how can it be interpreted?

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