mass spectrometry Flashcards
what is the mass spectrometry?
methods which gives accurate information about isotomic mass, abundance, and relative molecular mass of certain isotopes in an element
what is a method of mass spectrometry?
time of flight
what is stage 1 of TOF?
ionisation
what are the two ways that a sample can be ionised?
electron impact and electrospray
how is the sample ionised using the electrospray method?
a sample is dissolved in a volatile solvent (where it evaporates easily) and injected through a hyperdermic needle with a high voltage tip
how are the particles in the sample ionised?
the particles are ionised by gaining an proton (H⁺) from the solvent as they leave the needle producing XH⁺ ions (ions with a single positive charge and a mass of Mr + 1)
what is the equation for the ionisation of a sample using the electrospray method?
X(g) + H ⁺ –> XH⁺ (g)
what is stage 2 of TOF?
acceleration
where are the positive ions accelerated and why?
through an electric field in an ion drift so that they all have the same kinetic energy
why do the positive ions need to have the same kinetic energy?
so the particles separate to their according masses
what is the velocity of each particle dependant on?
dependant on it’s mass. lighter particles have a faster velocity and heavier particles have a slower velocity
if particle is lighter will it reach the detector first?
yes, as the lighter particle has a faster velocity so it will reach the detector first
what is the equation that links kinetic energy, velocity and mass?
ke= mv² / 2
what is the equation for v²
d² / t²
how to calculate the mass in kg of one ion (mass needed for TOF calculations)
Mr (which is in grams) / 1000 = kg
then ans / 6.022x10²³
what is stage 3 of TOF?
detection
what does the positive charged ions hit in order to be detected? why?
a negative plate to produce a electrical current as they gain electrons from the plate which generates a movement of electrons hence why it produces an electrical current
why is the detector connected to produces the results?
the detector is connected to a computer which produces a spectrum
how is abundance determined?
size of current is proportional to abundance
what does a mass spectrum show?
the mass to charge ratio (m/z) and the abundance of each ion
what does the m/z represent?
the mass to charge ratio. however, as the ions are produced by gaining an proton (1+ charge), the m/z is the mass of the ion
what is another type of mass spectometery?
electron bombardment
how is an ion form using the electron impact method?
the sample is hit using high energy electrons which leads to the sample molecule losing an electron
what is the equation for the ionisation of a sample using the electron impact method?
X(g) + e⁻ –> X⁺ (g) + 2e⁻
