Pharmaceutical Analysis (M.Pharm) INTRODUCTION INTERFERENCES IN ATOMIC ABSORPTION SPECTROSCOPY INTERFERENCES IN ATOMIC EMISSION SPECTROSCOPY

1. INTERFERENCES IN ATOMIC ABSORPTION
SPECTROSCOPY (AAS) AND ATOMIC EMISSION
SPECTROSCOPY (AES)
PRESENTED BY :
AKHILAA
1st YEAR M PHARM
PHARMACEUTICS
NGSMIPS

2. CONTENTS
 INTRODUCTION
 INTERFERENCES IN ATOMIC ABSORPTION SPECTROSCOPY
 INTERFERENCES IN ATOMIC EMISSION SPECTROSCOPY
 CONCLUSION
 REFERENCES

3. INTRODUCTION
 Interferences - physical or chemical processes - signal from the analyte in the
sample to be higher or lower than the signal from an equivalent standard.
 Interferences  positive or negative errors in quantitative analysis.

4. INTERFERENCES IN AAS
 2 major classes
i. Non-spectral interference – affects the formation of analyte free atoms.
ii. Spectral interference- amount of light absorbed to be higher –other than analyte
 Various types of Interferences:
1. Spectral Interference
2. Chemical Interference
3. Ionization Interference
4. Bulk or Matrix Interference
5. Background Absorption Interference
6. Non- Atomic Absorption Interference
7. Solvent Interference

5. 1) Spectral interference
• Refers to overlap of analyte signal. Normally occurs when absorption of an interfering species
either overlaps or lies very near to the analyte absorption.
• High temperature of the flame results in spectral interferences because a greater number of
spectral lines is produced.
Correction:
i. Avoided by removing the element by extraction method or by using calibration curve.
ii. By qualitative analysis, use a different line which is less sensitive.
Examples:
 Iron emits the radiation (spectrum) at 3247.28 Å ,
which is overlapped by radiation emitted by copper at 3247.54 Å.
NOTE: Interference due to overlapping lines is rare in AAS.

6. 2) Chemical interference
occur due to reaction between the atoms to be analysed and other materials present in the solution.
i. Anion interference
o The intensity of radiation emitted by the atoms under analyses is decreased due to the presence of
certain anions like aluminate, oxalate, phosphate, sulphate etc., in the solution.
o There is formation of stable compound (Refractory compound).
Example:
3𝐶𝑎2+ +2PO4
3- Ca3(PO4)2
• Correction methods
ii) Cationic Interference
 Cations can also cause interference, e.g., Al3+, if present as an impurity in Mg2+ reduces
atomization of the Mg2+ element.

7. 3) Ionization Interference
 Arises in if the flame temperature is too high. When this occurs the number of vaporized atoms
becomes ionized by the flame.
 Correction: Minimized by the addition of more easily ionizable elements.
 Examples: Ionization interference of calcium may be corrected by the addition of large quantities
of Na+ or K+ salts to the solution, Na+ or K+ is more readily ionized than Ca2+, this produces a high
concentration of electrons in the flame.
4) Bulk interference
A change in the viscosity of solution caused by either change in solvent or by change in
concentration may result in matrix or bulk interference.
 Correction: To avoid differences in the amount of sample and standard reaching the flame, it is
necessary that the physical properties of both be matched as closely as possible.

8. 5) Background Absorption Interference
 These types of interferences occur due to nature of the flame, sample matrix, scattering and
absorption of radiations by similar alkali salts mainly halides present in the sample solution.
 Flame background occurs due to scattering of radiation in monochromators.
 Correction: Grating monochromators
6) Non-atomic Absorption Interference
 Non-atomic absorption is caused by molecular absorption or light scattering by solid particles in
the flame.
 The absorption measurement obtained with a hollow cathode lamp is the sum of the atomic
absorption and the non-atomic absorption.
 Correction: The interference is corrected by making a simultaneous measurement of the non-
atomic absorption using a continuous source (usually deuterium).

9. 7) Solvent Interference
 In general, metals in aqueous solution gives lower absorbance, than same concentration of such
elements in an organic solvent.
Correction: Use of organic solvents like amines, ethers reduce solvent interference

10. INTERFERENCES IN AES
1. Spectral interference
2. Background emission
3. Chemical interference
4. Oxide formation interference
5. Interference due to foreign element
6. Interference due to salts and acids
7. Matrix effects
8. Interference due to molecular absorption

11. 1) Spectral interference
 It is encountered while isolating the desired radiant energy.
 The line of emission of the element to be determined and those due to interfering substances are
of similar wavelength.
Examples: Iron line at 324.728 nm overlaps the copper line at 324.574 nm and other iron line at
285.213 nm overlaps the magnesium line at 285.212 nm.
Correction:
i) By using calibration curves the effect of interfering elements is removed.
ii) It is also removed by improving the resolution of the instrument.
2) Background interference
 Interference may arise from the emission band spectra produced by molecules or molecular
fragments present in the flame gases.
Example: Band spectra due to hydroxyl and cyanogen radicals arise in many flames.
 Background effect can also be caused by light scatter. It is eliminated by using blank solution.

12. 3) Chemical interference
 The production of ground state gaseous atoms may be inhibited by two main forms of chemical
interferences:
 Overcome by increasing flame temperature, use of releasing agents.
 There are two types:
i) Cation interference
 Mutual interferences of cations have been observed, resulting in a reduced signal intensity of the
element being determined.
 These interferences are neither spectral nor ionic in nature.
 Example: Aluminium interferes with calcium and magnesium. Also, sodium and potassium show
cation-cation interference on one another.
ii) Anion interference
 The presence of certain anions, such as oxalate, phosphate, sulphate and aluminate, in a solution may
affect the intensity of radiation emitted by an element, resulting in serious analytical error
Example: Calcium in the presence of phosphate ion forms a stable substance as Ca3(PO4)2 which does not
decompose easily, resulting in the production of lesser atoms. Thus, the calcium signal is depressed.

13. 4) Oxide formation interference
 It arises due to the formation of stable oxide with free metal atoms, if oxygen is present in the
flame.
 Thus, the emission intensity is lowered because a large percentage of free metal atoms have been
removed from the flame.
 It is minimised by using very high temperature flames to dissociate the oxides producing free
atoms for excitation or using oxygen deficient environment to produce excited atoms.
5) Interference due to foreign elements
 This interference depends upon the quality of monochromator, source of temperature and the
concentration ratio between the contaminant and the element sought.
 Thus, the appropriate filter will minimize the interference.

14. 6) Interference due to Salts and Acids
 Large amount of salts and acids lower the metallic emission intensity.
 Use of releasing agents or protective chelating agents overcome these types of interference.
7) Matrix effects
 Matrix effects are physical factors which influence the amount of sample reaching the flame and
are related to viscosity, surface tension, density, vapor pressure and volatility of the solvent used
to prepare the test solution.
 If a series of standard is to be compared with a test solution, it is essential that the same solvent
should be used for each and the solution should not differ widely in their bulk composition.

15. 8) Interference due to molecular absorption
 In an acetylene-air flame a high concentration of sodium chloride will absorb radiation at
wavelength 213.9 nm, which is the wavelength of the major zinc resonance line.
 Hence sodium chloride would interfere in the determination of zinc under these conditions.
 It can be avoided by choosing a different resonance line or by using a hotter flame resulting in
increase in the operating temperature, thus le

16. CONCLUSION
Here, we discussed regarding the interferences in AAS and AES along with the examples and
correction methods. So, the interferences are confined mainly to phenomenon that affects the number
of atoms in the flame. AAS is less liable to be affected by interferences, when compared to AES.
Essentially the same interferences occurs in AAS and AES , but in somewhat different extends. By
the adequate control of these interferences, we can achieve a good analytical result.

17. REFERENCES
 Chatwal G.R, Anand S.K. Instrumental Methods of Chemical Analysis. 5th ed. New Delhi:
Himalaya Publishing House; 2.355-2.3599, 2.380-2.382.
 Tiwari Abhishek. Instrumental Methods of Analysis. 1st ed. Pune: Nirali Prakashan, 2020; 4.14-
4.16.
 Walode S.G, Chandan R.S. Instrumental Methods of Analysis. 1st ed. Pune: Nirali Prakashan,
2020; 4.21-4.23, 5.12-5.15.
 Robinson J.W, Skelly Frame E.M, Frame II G.M. Undergraduate Instrumental Analysis. 6th ed.
New York: Marcel Dekkar, 2005; 410-417, 455-458.
 Kar Ashutosh, Pharmaceutical Drug Analysis. 1st ed. New Delhi: Minerva Press, 2001; 484- 486.
 Kaur H, Instrumental Methods of Analysis. Meerut: Pragati Prakashan, 2011; 615-616.

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