Mass Spectrometry Flashcards
What is mass spectrometry?
It is a technique used to measure the relative mass of molecules
What does mass spect help to do?
- Verify identity of a drug substance
- Confirm the presence of a particular drug
- Verify the presence of drug and drug metabolites in clinical samples
What is M+?
Molecular ion - has the highest molecular mass but it isn’t always the most abundant peak due to fragmentation
How is sample vaporisation achieved?
By using heat, a vacuum or FAB
How are ions generated?
By bombarding the volatilised molecules with electrons from the electron gun
How does electron impact ionisation work?
The sample is vaporised by heat. Volatilised molecules are bombarded with an electron beam which fragments the molecule
What happens to +ve fragments from EI?
They are accelerated under a vacuum through a magnetic field into the deflection chamber and are analysed on the basis of M/Z ratio
How does chemical ionisation work?
A stream of electrons ionises a reagent gas which results in the production of strong acid
What kind of fragment is produced in chemical ionisation?
[M+H]+
What kind of molecules are EI and CI suitable for?
Small volatile molecules with a MW <1000 Da
How does fast atom bombardment work?
An analyte sample is suspended in a viscous matrix with a beam of fast moving Xe atoms.
Is ionisation necessary in FAB?
No because everything is done in one step
What is FAB suitable for?
Analysis of biomolecules, it is suitable for molecules with a MW up to ~6000
How does matrix assisted laser desorption ionisation work?
Energy is transferred to the matrix from a laser beam and the matrix must have a chromophore absorbing energy at a wavelength of laser
What is MALDI suitable for?
Biomolecules with a MW up to ~500000
How does electrospray ionisation work?
Analyte is dissolved in an organic solvent. A pH modifier is used to produce ions. Ionisation proceeds via protonation or deprotonation mechanism
How does atmospheric pressure chemical ionisation work?
An organic solvent is used to dissolve the sample and pH modifiers are also used
What is ESI normally used for?
Polar analyses
What is an advantage of APCI?
it can be used at atmospheric pressure so a vacuum isn’t needed
What is the order of the degree of fragmentation for the different techniques?
EI > CI»_space; FAB, ESI, APCI, MALDI
What are tandem mass spectrometry techniques based on?
An appropriate combination of mass spectrometry with other analytical methods
Which are the 3 most important tandem MS techniques?
Gas Chromatrography-MS
High performance Liquid Chromatography-MS
MS-MS
What is GC-MS used for?
Analysis of non-polar, volatile analytes
How does GC-MS work?
Interfacing a GC system to an MS instrument allows to separate the components of analyte and obtain mass spectrum for each point on the chromatogram. Unique fragmentation fingerprints can be used for compound identification. Using a library of standard MS spectra it is possible to identify and unknown analyte
How does HPLC-MS / LC-MS work?
Separates out components of a mixture and provides a MS profile on each fraction
