Mass Spectrometry Flashcards
What are the main components of a MS
SampleIonisationMass analyserDetectorData acquisition and analysis
Which elements of an MS are required to be in a vacuum
Mass analyser and Detector
What is the level of pressure needed for an ‘ultra-high’ vacuum
< 10 ^-7
What equipment is needed to achieve an ultra-high vacuum
Turbo pumps
Why is a vacuum necessary for MS
To prevent species from colliding into an air molecule (?)
What are the units of the mass/charge ratio
Thompson (Th)
What are the two modes of mass measurement and how are they achieved
Positive-ion mode (proton added)Negative-ion mode (proton taken away)
Define an isotope
An atom with the same number of protons/electrons but a different number of neutrons
Why are bromine ions annoying
Because the two isotopes of bromine are equally abundant, so mass spec gives two equal peaks
What is the relationship between the distance between isotope peaks and charge state
Inverse relationship.+1 charge gives peaks 1 Dalton apart.+2 charge gives peaks 0.5 Dalton apart.+4 charge gives peaks 0.25 Dalton apart
What is the equation to work out resolution
Resolution = Mass of 2nd peak / Resolving power R = M / delta M
What is better; higher or lower resolution
Higher - allows for better individual peak identification
What are the main ionisation techniques
Electrospray ionisation (ESI)Matrix-assisted laser desorption/ionisation (MALDI)Electron Ionisation (EI)Chemical Ionisation (CI)Fast-Atom Bombardment (FAB)
What is the main idea behind Electrospray Ionisation (ESI)
Adding voltage to a liquid forces the atoms (charged) to separate and become nanoparticles (which can be run through the MS)
What are the main advantages of Electrospray Ionisation (ESI)
‘soft’ ionisation technique - used in solution. Allows analysis of biological samples that are defined by non-covalent interactions.Able to ionise samples with large masses. Can easily be coupled with separation techniques (e.g. nano-LC)
What are the main disadvantages of Electrospray Ionisation (ESI)
Not good at analysing mixtures.Becomes contaminated easily, and difficult to clean. Extra charges added can give skewed results
What is the equation to work out molecular mass from an Electrospray Ionisation-MS graph
n = [M(n+1) - H] / [M(n) - M(n+1)]where n = molecular mass; M = m/z values for different peaks
What does MALDI stand for
Matrix-assisted Laser Desorption/Ionisation
How does MALDI work
Sample ‘co-deposited’ with ‘Matrix’. Laser excites matrix. Matrix transfers energy to sample. Produces singly charged species.
What is necessary for a MALDI matrix
Strong absorption of laser wavelengthLow sublimation tempGood mixer/solvent compatibility with sampleAble to participate in a photochemical reaction
Give examples of Matrices used in MALDI
DHBCHCAHPADithranolSinnapinic acid
What is the normal ratio of sample/matrix in MALDI
1:10,000Lots of matrix, very little sample.
Name some applications of MALDI
Find mass of an intact proteinFind molecular weight distribution of polymers
What are the main advantages of MALDI
‘gentle’ techniqueSamples with a high MW can be analysedMolecules don’t need to be volatileEasy to get sensitive resultsCan give a variety of charge states (1-3; +ve or -ve)
