Question

In complete cohesive sentences explain how Mass Spectrometry Instrument work (illustrate your explanation by drawing a schematic diagram of the instrument) What are the mechanisms involved inonic separation? What affects resolution? What are the major uses of this instrument?

Answer 1

Mass Spectroscopy is an analytical technique for the determination of the composition of a sample or molecule and elucidation of the chemical structures of molecules.Mass spectrometry has been described as the smallest scale in the world, not because of the mass spectrometer’s size but because of the size of what it weighs -- molecules.Mass Spectroscopy involves ionization of neutral molecules and fragmentation followed by grouping of the ionized species on the basis of their charge to mass (m/z) ratios for detection and quantitation

The main Parts of a MS Instrument is as follows.

1.sampler injector port

2. Ion Sourse

3. mass analyser

3. Detector

4.Data Analysis

In a MS instrument, a sample (solid, liquid, or gas,) is ionized by bombarding it with electronsor with any other ionisation techniques. Thus some of the sample's molecules may break into charged fragments. These ions are then separated according to their mass-to-charge ratio.The ions are detected by a mechanism capable of detecting charged particles, such as an electron multiplier. Results are displayed as spectra of the relative abundance of detected ions as a function of the mass-to-charge ratio called MS Spectrum.

Mechanism can be simply explaines as bellow.

Mass spectrometry is an analytical technique that can provide both qualitative (structure) and quantitative (molecular mass or concentration) information on analyte molecules after their conversion to ions.

The molecules of interest are first introduced into the ionisation source of the mass spectrometer, where they are first ionised to acquire positive or negative charges. The ions then travel through the mass analyser and arrive at different parts of the detector according to their mass/charge (m/z) ratio. After the ions make contact with the detector, useable signals are generated and recorded by a computer system.

The computer displays the signals graphically as a mass spectrum showing the relative abundance of the signals according to their m/z ratio

Ionisation

The atom or molecule is ionised by knocking one or more electrons off to give a positive ion.Most mass spectrometers work with positive ions.The ions are then moved to the mass analyzer by magnetic or electric fields.

There are different type of ionisation methods available.

• Electron bomb Ionization (EI)

•   Chemical Ionization (CI)

•   Field ionization (FI)

•   Matrix Assisted Laser Desorption Ionization ( MALDI)

•   Fast atom bombardment (FAB)

•   Electro Spray Ionization (ESI)

Electron bomb Ionization (EI): Sample is heated and energized by a beam of electrons, usually gives a molecular ion (M+) and a lot of fragments.

Chemical Ionization (CI): In chemical ionization sources, the analyte is ionized by chemical ion-molecule reactions during collisions in the source.

Electro Spray Ionization (ESI): ESI produce ions using an electrospray in which a high voltage is applied to a liquid to create an aerosol. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized.

Matrix Assisted Laser Desorption Ionization ( MALDI): It uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation. It is very usefull in the analysis of biomolecules and large organic molecules which tend to be fragile and fragment when ionized by more conventional ionization methods.

Acceleration

The ions are accelerated so that they all have the same kinetic energy.

Deflection

The ions are then deflected by a magnetic field or an electric filed according to their masses. Lighter masses are deflected more.The amount of deflection also depends on the number of positive charges on the ion

Mass analyser

.The magnetic field is scanned to measure different ions.

Types of mass analyzer:-

   (1) Quadrapole mass filter.

   (2) time of flight

   (3) Ion trap

   (4) Fourier transform ion cyclotron resonance (FT-ICR or FT-MS).

Detector

The ions are then dected by using a detector.The detector records either the charge induced or the current produced when an ion passes by or hits a surface.

Application of MS

Mass spectrometry has both qualitative and quantitative uses.

• Molecular weight determination
• Identifying unknown compounds
• Determining the structure of a compound by observing its fragmentation.
• Quantifying the amount of a compound in a sample
• Determining the isotopiccomposition of elements in a molecule
• Determination and quantification of pesticides in food samples.
• In pharmacokinetics studies.
• In the characterization and sequencing of proteins.
• In biological and chemical research.
• Identify a protein from the mass of its peptide fragments.
• Determine structures of drugs and metabolites.
• Test food and beverages for contamination, adulteration and product consistency.