Spectroscopic Methods and more week 6

Question 1

MASS SPECTROMETRY (MS)

Answer 1

Molecule resolution data

FAST (up to 500 spectra/sec)

Works for mixtures and pure compounds

Single molecule MS is possible – routinely ng/pg per ml concentrations

Question 2

ELEMENTS

Answer 2

unique proton number

Question 3

isotope

Answer 3

different neutron number

Question 4

The effect of isotopes is

Answer 4

additive

Question 5

average mass

Answer 5

The mass of the molecule that accounts for the average isotopic distribution.

Question 6

accurate mass
monoisotopic

Answer 6

The mass of the molecule that consists only of the principle isotopes.

Question 7

Nuclear binding energy

Answer 7

Nuclear binding energy holds protons and neutrons together in a nucleus.

As different elements/isotopes have different numbers of protons and neutrons the energy needed to hold them together is different

Question 8

Mass spectrometers can

Answer 8

ONLY detect ions.

Question 9

cation

Answer 9

Loss of an electron (mostly pi or inorganic systems)
[M]+

Question 10

an anion

Answer 10

Loss of an acidic proton (eg carboxylic acids)
[M-H]-

it cannot lose inner proton

Question 11

Ion separation in mass spectrometers depends on the

Answer 11

ion’s mass to charge ratio

m/z

Question 12

HARD

Answer 12

High energy ionisation processes
Con: Too much energy can cause molecules to break apart (fragment)

Pro : Ionisation of ‘difficult’ molecules

Question 13

SOFT

Answer 13

Low energy ionisation processes

Con: Too little energy – might be insufficient to ionise certain molecules

Pro : Little/No fragmentation

Question 14

Electron ionisation (EI) is

Answer 14

hard ionisation

Question 15

Electron ionisation (EI) steps

Answer 15

1. sample is gaseous
2. filament wire has a current. Electrons collide with typically lone pairs of electrons or electrons in multiple bonds.
3. the analyte loses an electron.
4. the high energy electron goes to trap electrode.
5. this creates an cation.

Question 16

electron ionisation description

Answer 16

Beam of electrons of wavelength close to bond length destructively interferes with bonding electrons causing an electron to be lost (mostly pi or inorganic systems)

Question 17

chemical ionisation description

Answer 17

Gaseous analyte reacted with a high energy source of protons… CH5+

Generates protonated molecular ions [M+H]+

Question 18

chemical ionisation is

Answer 18

hard but not too hard.

Question 19

chemical ionisation steps

Answer 19

1. gaseous sample molecules collide with positive reagent ions.
   they react.

Question 20

electrospray ionisation

Answer 20

Solvent is evaporated from charged droplets of analyte in solution leaving the molecule as either …
cationised eg. [M+H]+ or anionised eg [M-H]-

Question 21

electrospray ionisation steps

Answer 21

1. capillary is attach to high voltage.
2. solution is dissolved in ionic compound.
3. it is dissolved.
4. it evaporates as voltage is applied.
5. solvents evaporates
6. columbic explosion as it near like ions

Question 22

electrospray ionisation is

Answer 22

soft for polar molecules

Question 23

magnetic

Answer 23

The radius that an ion path is curve is dependent on the m/z ratio of the ion and the magnetic field strength

Question 24

rods

Answer 24

4 rods , 2+, 2-.

there is a voltage.
only ions with desire m/z can travel.
others are neutralised.