ANALYTICAL TECHNIQUES FOR ANALYSIS OF INORGANIC ELEMENTS – A REVIEW

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INSTRUMENTATION [4]
•    inductively coupled plasma source
•    Nebulizer
•    Pumps
•    Spray chambers
•    Torch
•    Radio frequency generators
•    Transfer optics
•    Wavelength dispersive  devices
•    Detector (photomultiplier; PMT)
•    Data collection


 

Figure 5. Inductively coupled plasma-atomic emission spectrometry (ICP-AES)

Sample introduction

NEBULIZER
the sample solution is acidified up to 2-3% in HNO3 to prevent adsorption of metals onto polypropylene sample bottle or onto instrument tubing or glassware prior to introduction into the plasma. Converts liquid sample into aerosol & is transported into plasma which excites the atomic species in the aerosol.

Two forces to break up this liquid
1.    Pneumatic forces
2.    Ultrasonic mechanical forces

PUMPS [5]    Peristaltic pumps are almost exclusively the pumps of choice There is a special tubing used in it where the sample is passed through it This is for the prevention of contamination of direct contact with the solution

SPRAY CHAMBERS Once the sample aerosol is created by nebulizer, it is transported to the torch & injected into the plasma[6]. A spray chamber is placed between nebulizer and torch.The primary function is to remove large particles from the aerosol.Secondary purpose is to smooth out pulses that occur during nebulization While smaller particles travel with the Ar flow and enter the torch. Evaporation, atomization, and excitations/ionizations occur in the plasma at temperatures reaching 10 000 K.

TORCH There are 3 tubes for argon flow & aerosol injection.The spacing between 2 outer tubes is narrow, so that gas emerges at high velocity The purpose of the torch is to (1) evaporate the solvent (usually water) from the analyte salts,(2) atomize the atoms in the salt (break the ionic bonds and form gaseous state atoms),(3) excite or ionize the atoms. The gas flow that carries the sample aerosol is injected into the plasma through central tube or injectorTorches are of 2 namely Mountable & Demountable

Figure 6. torch

RADIO FREQUENCY GENERATORS It is the device that provides the power for the generation & sustainment of the plasma discharge  power (700 to 1500 watts)  is transferred to plasma gas through a load coil surrounding the top of the torch.2 types namely   1.Crystal controlled generators 2.Free running generators. 

WAVE LENGTH DISPERSIVE DEVICES physical dispersion- diffraction grating.Prisms ,filters,interferometers, Echelle grating most commonly used.The Rowland system utilizes a concave Echellette-style grating monochromator .monochromatic radiation is composed primary of wavelenths representative of the light emitted by a particular elemental or molecular species just like musical instruments which produce harmonics of sounds.Multi element analysis is possible with conventional polychromators where each slit aligned to allow a specific wavelength of radiation to pass to a detector  

DETECTORS Once the proper emission line has been isolated by the spectrometer[7] detected measures  the intensity of the emission, By far the most widely used detector is Photo multiplier tube It is a vacuum tube contains photo cathode that ejects electrons when it is struck by light. These ejected electrons are accelerated towards dynode which ejects 2 to 5 secondary electrons for every electron which strikes at surface. the secondary electrons[8] strikes another dynode ejecting more electrons causing multiplicative effect.The  final step is the collection of secondary electrons from the last dynode by the cathode.

Conclusion
Flame photometry is crude but cheap compared to Atomic Absorption spectrometer. Atomic Absorption spectrometer can be used to determine over 70 different elements in solution or directly in solid samples used in pharmacology, biophysics and toxicology research. Atomic absorption spectrometry has many uses in different areas of chemistry such as clinical analysis of metals in biological fluids and tissues such as whole blood, plasma, urine, saliva, brain tissue, liver, muscle tissue, semen, in some pharmaceutical manufacturing processes, minute quantities of a catalyst that remain in the final drug product, and analyzing water for its metal content.

REFERENCES
1.  https://en.wikipedia.org/wiki/Photoelectric_flame_photometer
2.  Atomic Spectroscopy,A Guide to Selecting the Appropriate Technique and System www.perkinelmer.com/Atomic Spectroscopy
3. Xiandeng Hou and Bradley T. Jones, Inductively Coupled Plasma/Optical Emission Spectrometry, R.A. Meyers (Ed.) pp. 9468–9485 . A. Walsh (1955).
4.The application of atomic absorption spectra to chemical analysis, Spectrochim. AA. Walsh (1955), The application of atomic absorption spectra to chemical analysis, Spectrochim. Acta 7: 108–117.
5.J.W.Robinson,Recent Advances in Atomic Absorption Spectroscopy, anal.Chem., 1961, 33 (8), pp 1067–1071
6.  Bauman, R.P. Absorption Spectroscopy, John Wiley, New York, 1965.
7.  Dean, J., Flame Photometry, McGraw-Hill, New York, 1960.
8.Ottaway, J., and A. Ure, Practical Atomic Absorption Spectroscopy, Pergamon, New York, 1983.

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