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Mass SpectrometryPRESENTED BYPHARMACISM

Mass Spectrometry Analytical method to measure the molecule or

atomic weight of sample. What information can be determined?

Molecular weight Molecular formula Structure Isotopic incorporation/distribution Protein sequence

Mass Spectrometry There are four key stages in the process for Mass

Spectrometry.

1. Ionisation

2. Acceleration

3. Deflection

4. Detection

Ionization & Fragmentation Electro Ionisation is the most common type of ionisation. The sample is bombarded by electrons which come from a heated

filament. The electrons run in a stream between the cathode and anode. When the sample passes through the electron stream, the high energy

electrons in the stream knock electrons out of the sample to form ions.

In the simplest case, ionization is the removal of an electron to give an atom with an overall +ve charge.

Acceleration Acceleration is a simple step where the ions are placed

between a set of charges parallel plates. The ions will then be repelled by one plate and attracted to the

other. There is a slit cut in the plate which the ions are attracted to.

the force of attraction and repulsion forces the ions through the slit at an accelerated rate.

The speed of acceleration can be adjusted by changing the charge on the plates.

Deflection Ions are deflected by the magnetic field surrounding the instrument. The amount of deflection depends on the mass and charge of the

ions. The heavier ions and ions with a positive charge of 2 or more, are

deflected the least (Ion stream C) The lightest ions and ions with 1 positive charge are deflected the

most (Ion Stream A) The ions at the correct mass and charge travel to the detector. (Ion

Stream B)

Detection When the ion stream reached the detector they hit a wire. On hitting the wire they become neutralized by an electron

jumping from the metal wire to the ion. The amplifier picks up on this current being created between

the wire and the ion and amplifies the signal being detected. The computer picks up on this and converts it to mass/charge

ratio and a spectrum is produced.

Mass Spectrum

Application Pharmaceutical analysis

Bioavailability studies Drug metabolism studies, pharmacokinetics Characterization of potential drugs Drug degradation product analysis Identifying drug targets

Biomolecule characterization Proteins and peptides Oligonucleotides

Environmental analysis Pesticides on foods Soil and groundwater contamination

Advantages & DisadvantageAdvantages:  Small sample size  Fast  Differentiates isotopes  Can be combined with GC and LC to run mixtures

Disadvantages: o Doesn't directly give structural information (although we can

often figure it out) o Needs pure compounds o Difficult with non-volatile compounds

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