Mass Spectrometry Flashcards
Define relative atomic mass
weighted average mass of one atom of an element relative to 1/12 the mass of an atom of carbon-12
Define the term molecular mass
weighted average mass of one molecule reactive to 1/12 the mass of one atom carbon-12
Define the term formula mass
weighted average mass of one ionic compound relative to 1/12 the mass of one atom carbon-12
How does electron impact ionise the sample in mass spectrometry?
firing high energy electrons from an electron gun/hot cathode at a vaporised sample-an electron knocked off forming a +1 ion
What is the equation for electron impact ionisation?
X(g) + e- -> X+(g) + 2e-
How does electrospray ionise the sample in mass spectrometry?
dissolving sample in volatile solvent and forced through a fine needle connected to positive terminal of high voltage supply-produces droplets that have gained a proton
How are ions accelerated in time of flight mass spectrometry?
positive ions attracted towards negatively charged plate to the same kinetic energy
Which ions are faster?
lighter ions and those with a greater charge
What is ion drift?
when ions pass through hole in negatively charged plate forming a beam
How are ions detected in ToF?
hit negatively charged electric plate and discharged by gaining electrons
Why is movement of electrons important in ToF?
Generates current which is measured to find out number of ions hitting plate
What is data analysis in ToF?
Computer produces mass spectrum which shows mass to charge ratio and abundance of each ion
What does the m/z value show?
Mass number of the ion
How can values in the mass spectrum be used to calculate relative atomic mass (Ar)?
(Mass number * abundance of ions) /
(Total abundance, 100)
What is the equation for Ke in ToF acceleration?
Ke=1/2mv^2
