About author :
Department of Pharmacy, Southern University Bangladesh, Chittagong-4200.
*e-mail: [email protected]
Pharmaceutical analysis has greatest importance in pharmaceutical science, specially in terms of Research & Development (R&D), Drug-Product design, Quality Control Department of a Pharmaceutical Industry. Among the number of spectroscopic analytical techniques, Mass Spectrometry occupied a large area of whole analytical zone. The very important issue in this technique is to generate the spectra to check out the relative abundance of the distinct ion that are generate & separate according to their mass to charge(m/z) ration. This is the impact factor of mass spectrometry.
Key words: Mass spectrometry, Molecular mass, Mass to charge (m/z) ration
Perspective of Mass Spectrometry
Mass spectrometry is a very essential quantitative & qualitative analytical technique that is designed & used for proper determination of molecular mass & molecular formula of a compound. In mass spectrometry, the record is called mass spectra which is a plot of relative abundance of peak/ ion vs mass to charge (m/z) ration.
Significances of mass spectra are:
1. Helps to prove the identity of a particular compound by comparing its spectra with standards spectra.
2. To determine the accurate molecular mass.
3. To determine the chemical structure by various method.
4. To detect the certain structures( functional group) in the whole compound.
5. To establish the molecular formula of the compound or analyte present in the sample.
6. A potential requirement for mass spectrometric analysis is “Mass Spectrometer”
7. A mass spectrometer converts them to ions so that they can be moved about and manipulated by external electric and magnetic fields
The four ssential functions of a mass spectrometer, and the associated components, are:
1. A small sample is ionized by increasing the volatility, usually to cations by loss of an electron.
2. The ions are sorted and separated according to their mass to charge (m/z).
3. The separated ions are then measured, and the results displayed on a spectra (mass spectra).
Ionization is very important role of mass spectrometer. It plays a vital role in ionizing the volatile or in-volatile material into the significant ion for further separation & spectra generation. But the method must vary in both case thus in case of volatile and in-volatile materials.
For Volatile materials, ionization done by-
1. Electron Impact
2. Chemical Ionization
For in volatile materials, ionization done by-
1. Field Desorption
2. Fast Atom Bombardment (FAB)
3. Laser desorption (High / Low resolution)
Electron impact (EI)
An EI source uses an electron beam, usually generated from a tungsten filament, to ionize gas-phase atoms or molecules. An electron from the beam knocks an electron off of analyte atoms or molecules to create ions.
Chemical ionization (CI)
CI uses a reagent ion to react with the analyte molecules to form ions by either a proton or hydride transfer:
MH + C2H5+ –> MH2+ + C2H4
MH + C2H5+ –> M+ + C2H6
The reagent ions are produced by introducing a large excess of methane (relative to the analyte) into an electron impact (EI) ion source. Electron collisions produce CH4+ and CH3+ which further react with methane to form CH5+ and C2H5+:
CH4+ + CH4 –> CH5+ + CH3
CH3+ + CH4 –> C2H5+ + H2
Fast-atom bombardment (FAB) :
In FAB a high-energy beam of neutral atoms, typically Xe or Ar, strikes a solid or low-vapor-pressure liquid sample causing desorption and ionization. It is used for large biological molecules that are difficult to get into the gas phase. The sample is usually dispersed in a matrix such as glycerol. FAB causes little fragmentation and usually gives a large molecular ion peak, making it useful for molecular weight determination. The atomic beam is produced by accelerating ions from an ion source though a charge-exchange cell. The ions pick up an electron in collisions with neutral atoms to form a beam of high-energy atoms.
After generation molecular ion , the ions are analysed by mass analyser below
1. Magnetic sector
3. Ion trap
Due to the efficiency of detection of the ion by mass analyser fluently, mass spectrometric analysis is well enable to develop mass spectra early after initiation of operation. Hence it’s a potential tool for modern analytical world. Drug-Product design & development process run smoothly by utilizing principles & tools of mass spectrometry. In recent years, mass spectrometry relates with liquid chromatography (LC-MS) for direct separation of moieties & their molecular formula generation with proper specification.