Interferences in AAS MCQs With Answer

Interferences in AAS MCQs With Answer

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Introduction

Atomic Absorption Spectroscopy (AAS) is central to quantitative elemental analysis in pharmaceutical research, yet its accuracy can be compromised by interferences originating from the sample matrix, the flame or furnace environment, and the instrument. This MCQ set focuses on understanding, predicting, and mitigating interferences in AAS—spectral, chemical, ionization, and physical—tailored for M. Pharm students. You’ll revise practical strategies such as background correction (Deuterium and Zeeman), use of releasing and protective agents, ionization buffers, flame selection, chemical modifiers for graphite furnace AAS, and calibration approaches like standard addition. Questions emphasize real laboratory scenarios, decision-making for method optimization, and recognizing the signatures of different interference types to ensure reliable, regulatory-compliant results.

Q1. Which grouping best represents the major types of interferences encountered in AAS?

  • Spectral, chemical, ionization, and physical (transport/matrix)
  • Thermal, mechanical, chromatographic, and optical
  • Photoelectric, radiative, acoustic, and magnetic
  • Nuclear, electrochemical, enzymatic, and photolytic

Correct Answer: Spectral, chemical, ionization, and physical (transport/matrix)

Q2. Formation of refractory compounds (e.g., oxides, phosphates) that reduce free atom population in the flame is characteristic of:

  • Spectral interference
  • Chemical interference
  • Ionization interference
  • Instrumental drift

Correct Answer: Chemical interference

Q3. To minimize ionization interference for alkali/alkaline earth elements in a hot flame, the most effective step is to:

  • Add an ionization buffer such as K or Cs salt to increase electron density
  • Use a deuterium lamp for background correction
  • Increase nebulizer gas flow to enhance aerosol formation
  • Decrease the spectral bandwidth using a narrower slit

Correct Answer: Add an ionization buffer such as K or Cs salt to increase electron density

Q4. In graphite furnace AAS, which background correction approach is most robust against strong broadband background absorption?

  • Deuterium continuum background correction
  • Zeeman effect background correction (magnetic modulation)
  • First-derivative spectrometry
  • Interelement correction using a multi-element lamp

Correct Answer: Zeeman effect background correction (magnetic modulation)

Q5. For analytes prone to forming refractory oxides (e.g., Al, Ti, V), which choice of flame typically minimizes chemical interference?

  • Air–acetylene, fuel-lean
  • Nitrous oxide–acetylene (hot, slightly fuel-rich)
  • Hydrogen–oxygen flame
  • Air–propane flame

Correct Answer: Nitrous oxide–acetylene (hot, slightly fuel-rich)

Q6. Phosphate interferes with Ca determination in FAAS. Which additive is commonly used as a releasing agent to overcome this interference?

  • Lanthanum chloride (LaCl3)
  • EDTA
  • Sodium chloride (NaCl)
  • Ammonium hydroxide (NH4OH)

Correct Answer: Lanthanum chloride (LaCl3)

Q7. In the context of AAS, a protective agent is best described as a substance that:

  • Complexes the interferent to prevent its atomization
  • Complexes the analyte to prevent refractory compound formation and enable easier atomization
  • Scavenges electrons to promote ionization of the analyte
  • Raises the flame temperature to enhance dissociation

Correct Answer: Complexes the analyte to prevent refractory compound formation and enable easier atomization

Q8. Which factor most directly causes physical (transport) interference in FAAS by altering aerosol generation and transport?

  • Overlap of emission lines in the lamp spectrum
  • Changes in sample viscosity and surface tension
  • Excitation of molecular bands in the flame
  • Photometric noise of the detector

Correct Answer: Changes in sample viscosity and surface tension

Q9. The method of standard additions is preferred when:

  • Certified reference standards are unavailable
  • The matrix composition is complex or unknown and likely to affect the signal
  • The calibration range is very wide
  • The analyte has multiple isotopes

Correct Answer: The matrix composition is complex or unknown and likely to affect the signal

Q10. Spectral interference in AAS typically arises due to:

  • Overlap of analyte absorption line by a line from a concomitant element or molecular band absorption/scattering
  • Variations in sample aspiration rate
  • Incomplete drying during furnace heating
  • Matrix-induced signal enhancement only

Correct Answer: Overlap of analyte absorption line by a line from a concomitant element or molecular band absorption/scattering

Q11. Optimizing burner height in flame AAS is primarily done to:

  • Reduce slit width and improve resolution
  • Position the observation zone at maximum free-atom population while minimizing background
  • Increase lamp intensity and improve S/N
  • Lower the flame temperature to reduce ionization

Correct Answer: Position the observation zone at maximum free-atom population while minimizing background

Q12. In GFAAS, which chemical modifier combination is widely used to mitigate matrix interferences by stabilizing the analyte during char and allowing higher ashing temperatures?

  • Palladium with magnesium nitrate (Pd/Mg(NO3)2)
  • Sodium borohydride (NaBH4)
  • Potassium cyanide (KCN)
  • Ammonium sulfate ((NH4)2SO4)

Correct Answer: Palladium with magnesium nitrate (Pd/Mg(NO3)2)

Q13. Memory effects (carryover) in GFAAS are best reduced by:

  • Using a wider spectral slit
  • Employing pyrolytic-coated tubes/platform and adding a high-temperature cleanout step
  • Increasing lamp current
  • Switching to a cooler flame

Correct Answer: Employing pyrolytic-coated tubes/platform and adding a high-temperature cleanout step

Q14. How do ionization buffers mitigate ionization interference in flame AAS?

  • They reduce solvent viscosity to improve nebulization
  • They increase electron density, shifting the ionization equilibrium toward neutral atoms
  • They scavenge electrons to prevent recombination
  • They cool the flame, preventing atomization

Correct Answer: They increase electron density, shifting the ionization equilibrium toward neutral atoms

Q15. Apparent absorbance due to turbidity or large aerosol droplets in the optical path is primarily caused by:

  • Rayleigh scattering from very small molecules only
  • Mie scattering from droplets/particulates in the flame or tube
  • Blackbody radiation of the flame
  • Photomultiplier dark current

Correct Answer: Mie scattering from droplets/particulates in the flame or tube

Q16. Adding 5–10% methanol to both samples and standards in FAAS is mainly intended to:

  • Enhance spectral resolution at the analytical line
  • Correct for physical interferences by matching viscosity/surface tension
  • Eliminate ionization by providing electrons
  • Remove phosphate interference by complexation

Correct Answer: Correct for physical interferences by matching viscosity/surface tension

Q17. Stray light reaching the detector in AAS most commonly leads to:

  • Inflated absorbance and positive bias at high analyte concentrations
  • Nonlinear calibration with depressed apparent absorbance at high analyte concentrations
  • Improved linearity across the dynamic range
  • Enhanced background correction performance

Correct Answer: Nonlinear calibration with depressed apparent absorbance at high analyte concentrations

Q18. High acid concentration (e.g., >2% v/v HNO3 or HCl) in samples can cause what predominant effect in FAAS?

  • Signal enhancement by increasing atomization efficiency for all elements
  • Signal suppression due to increased surface tension/viscosity affecting nebulization
  • Elimination of all chemical interferences
  • Complete removal of background absorption

Correct Answer: Signal suppression due to increased surface tension/viscosity affecting nebulization

Q19. The L’vov platform (platform atomization) in GFAAS helps reduce matrix effects mainly by:

  • Lowering the furnace temperature during atomization
  • Providing thermal equilibration and delayed atomization, allowing matrix to be removed before atom release
  • Increasing the optical path length
  • Eliminating the need for background correction

Correct Answer: Providing thermal equilibration and delayed atomization, allowing matrix to be removed before atom release

Q20. A large difference between background-corrected and uncorrected absorbance readings at the analytical wavelength indicates:

  • Predominant nonspecific background due to molecular absorption/scattering
  • Stable instrument with no interference
  • Pure spectral line absorption only
  • Only ionization interference is present

Correct Answer: Predominant nonspecific background due to molecular absorption/scattering

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