3.1.1 Mass Spec

What type of particles are used for electron impact

elements and molecules with a low MR

How does electron impact work

high-energy electrons are fired at the sample from an electron gun towards a positively charged plate. the electron impact knocks off one electron from each particle to form a 1+ ion

Electron impact equation

X (g) -> X+ (g) + e-

What type of particles are used for electrospray ionisation

molecules with a higher Mr

How does electrospray ionisation work

sample is dissolved in a volatile solvent and injected into the vacuum ionisation chamber through a hypodermic needle. the needle is positively charged so each molecule gains a proton. the solvent then evaporates

Electrospray ionisation equation

X (g) + H+ -> XH+

How are the ions accelerated

using an electric field so they all have the same kinetic energy

How does separation of charged ions work

ions with different masses have a different time of flight. smaller ions have a shorter time of flight

How does detection work

the ions hit the detector and gain an electron which produces a current. the more electrons hitting the plate, the larger the current

What is the detector

a negatively charged plate

What are peaks below the actual mass number due to on a mass spectra?

fragmented ions

What are peaks above the actual mass number due to?

isotopes like C-13 or H-2

relative atomic mass

the weighted average mass of all the isotopes of an element compared to 1/12th the mass of a Carbon-12 atom.

Equation linking KE, m and v

KE = 1/2 mv^2

Equation linking t, d and v

t = d/v

Equation linking t, d, v, m and KE

t = d sqrt (m/2KE)

Molecular mass

the weighted average mass of a molecule compared to 1/12th of the mass of a Carbon-12 atom