W8 Mass Spectromotry

Question 1

What is mass spectrometry

Answer 1

Mass spectrometry is an analytical technique

that involves the ionisation of chemical species

then sorting of the ions based on their mass to charge ratio

Question 2

What are the main things it is used for

Answer 2

Obtaining details about

• mass of a chemical species
• structural information about molecules

Question 3

What are advanced ms techniques used for

Answer 3

analyze complex mixtures including ones which contain biomolecules e.g. carbohydrates or proteins

Question 4

What are the 3 main areas mass spectrometry is used

Answer 4

biomolecule characterization

environmental analysis

forensic analysis/clinical

Question 5

What is a Dalton

Answer 5

one unit of mass and is defined as 1/12th the mass of a single carbon 12 atom

Question 6

What is an isotopologues

Answer 6

it is a molecule that differs only in isotopic composition

Question 7

How does the size of a molecule affect its chance to have a less abundant isotope

Answer 7

the larger the molecule the chance to have more than one atom of a less abundant isotope is higher

Question 8

What is a characteristic of Isotopologues on a graph

Answer 8

peak splitting

Question 9

What are the main components of a mass spectrometre

Answer 9

the machines consist of

an ion source

mass analyzer

detector

Question 10

What is the 1st step an ms follows

Answer 10

the sample is vaporised and ionised

Question 11

what is the 2nd step an ms follows

Answer 11

ions subject to a filter to separate them according to their mass to charge ratio

Question 12

what is the 3rd step an ms follows

Answer 12

the stream of mass separated ions are detected

Question 13

what is the 4th step an ms follows

Answer 13

an electrical output is generated producing a plot of the signal intensity for each mass to charge ratio.

Question 14

What are the steps an ms follows

Answer 14

the sample is vaporised and ionised

ions subject to a filter to separate them according to their mass to charge ratio

the stream of mass separated ions are detected

an electrical output is generated producing a plot of the signal intensity for each mass to charge ratio.

Question 15

What is the highest peak in a ms known as

Answer 15

base peak

Question 16

what is a base peak

Answer 16

it is the highest peak in a ms and is set to 100% relative intensity

Question 17

What is a molecular ion peak

Answer 17

the signal that represents the mass of the target compound

Question 18

what is the units of the x axis in ms

Answer 18

Mass / Charge (M/Z)

Question 19

Why are there many peaks on the mass spec

Answer 19

there are many peaks as they are the fragments of the molecule

Question 20

What are the two main types of mass spectrometry techniques

Answer 20

Electron Impact Ionization (EI)

Matrix assisted laser desorption ionisation (MALDI)

Question 21

What happens in Electron Impact Ionization

Answer 21

The vaporized sample gets bombarded with high energy electrons causing an electron from the compound to be ejected.

This makes the compound a high energy charged species,

which can then breakdown into lower weight fragment ions and radicals

Question 22

What is the first step of EI MS

Answer 22

Sample vaporised and ionised

Question 23

What is the second step of EI MS

Answer 23

Ions accelerated in an electric field

Question 24

What is the third step of EI MS

Answer 24

In the magnetic sector circular flight path adopted dependent upon the mass to charge ratio

Question 25

What is the fourth step of EI MS

Answer 25

Changing magnetic field strength allows only ions of correct M/Z ratio through the detector

Question 26

What is the fifth step of EI MS

Answer 26

Spectrometer operates by sweeping the magnetic field to scan hte mass range

Question 27

What is the process of EI MS (Simplefied)

Answer 27

Sample Vaporized and Ionized Ions accelerated Circular flight path can be adopted dependent of mass to charge ratio change in magnetic field allows what we want to be detected spectrometer scans magnetic field for mass range

Question 28

what can explain fragments

Answer 28

homolyic alpha cleavage heterolytic alpha cleave these are both pathways that can explain

Question 29

What does homolytic alpha cleave often do

Answer 29

it often gives the most abundant ion the radical is often used to form a double bond with the heteroatom loss of the largest possible radical favoured

Question 30

What can we get in addition to fargmentation

Answer 30

we can also get rearrangements

Question 31

what is the mclafferty rearrangement

Answer 31

It is a process which can be undertaken by aliphatic ketones aldehydes that feature gamma hydrogens (Must have at least alkyl chain of three carbons) carboxylic acids esters amides

Question 32

Describe Maldi MS

Answer 32

softer low energy ionisation technique

Question 33

what happens to the sample in Maldi MS

Answer 33

mixed with a matrix compound that is a strong uv absorber

Question 34

why is the sample mixed with a strong uv absorber matrix

Answer 34

its function is to absorb energy from a pulsed ultraviolet laser and transfers it to the sample