Organic Analysis

Question 1

What is time of flight mass spectrometry used for?

Answer 1

-used to measure the relative mass of isotopes

-used in pharmaceutical/forensic/environmental analysis

Question 2

ToFMS Stage 1: Ionisation (Electrospray)

Answer 2

• sample is dissolved in a volatile polar solvent and injected through a needle at a high voltage
• Each particle gains a proton and becomes a 1+ ion

Question 3

ToFMS Stage 1: Ionisation (Electron Impact)

Answer 3

• high energy electrons are fired from an electron gun which knock off an electron each
• This forms 1+ ions

Question 4

ToFMS Stage 2: Acceleration

Answer 4

-positive ions are accelerated by an electric field to a constant kinetic energy

-velocity depends on mass of the ion

Question 5

ToFMS Stage 3: Ion Drift

Answer 5

• ions go through a tube of known distance and time that it takes to reach the detector is recorded
• heavier ions take longer to reach detector
• lighter ions reach the detector faster

Question 6

ToFMS Stage 4: Ion Detection

Answer 6

• positive ions hit a negatively charged plate and pick up ab electron each
• this flow of electrons produces a current which is directly proportional to the abundance of the isotopes

Question 7

Working out the time or mass of an isotope when given time or mass of another

Answer 7

m1/(t1)^2=m2/(t2)^2

Question 7

ToFMS Stage 5: Data Analysis

Answer 7

• the detector is linked to an amplifier and then to a recorder which converts the current into a peak that is shown in a mass spectrum
• the height of the peak is proportional to the abundance of ion

Question 8

How to work out mass of one 1+ particle

Answer 8

m = (mass number ÷ Avogadro’s Constant)/1000

Question 9

how would you find the Mr of a sample from the m/z values (TOF mass spectrometry) when doing electron impact ionisation

Answer 9

the Mr is equal to the peak with the greatest m/z value

Question 10

how would you find the Mr of a sample from the m/z values (TOF mass spectrometry) when doing electrospray ionisation

Answer 10

the Mr is equal to the peak with the greatest m/z value minus one

Question 11

how does infrared spectroscopy work

Answer 11

A beam of IR radiation is passed through a sample of a chemical, and is absorbed by covalent bonds in the molecule (increasing vibrational energy). Different bonds absorb different amounts of radiation, and stretch and bend accordingly creating a frequency that’s measured in wavenumber

Question 12

what is the fingerprint region in infrared spectroscopy

Answer 12

• the area below 1500cm⁻¹ which is unique for any particular substance and can be used to identify the compound

Question 13

how are the polarity of bonds and absorption of infrared radiation linked

Answer 13

the more polar the bonds, the more IR radiation the bonds absorb