Atomic absorption spectroscopy – principle, instrumentation, interferences and applications MCQs With Answer

Atomic absorption spectroscopy (AAS) is a sensitive analytical technique widely used in pharmaceutical analysis for trace metal determination. This introduction covers the AAS principle — generation of free ground‑state atoms and element‑specific light absorption — and key instrumentation: hollow cathode lamps, nebulizers, burners, graphite furnaces, monochromators, and photomultiplier detectors. It explains common interferences (spectral overlap, chemical reactions, ionization, and matrix effects) and practical remedies (background correction, matrix modification, standard addition). Applications include drug quality control, excipient testing, dissolution/contamination assessment, and environmental monitoring. Emphasis on sensitivity, selectivity, important aspects of calibration, and sample preparation prepares B. Pharm students for analytical challenges. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the fundamental principle of atomic absorption spectroscopy (AAS)?

• Emission of light by excited atoms
• Absorption of element-specific radiation by ground-state atoms
• Scattering of light by particles in solution
• Fluorescence from molecular species

Correct Answer: Absorption of element-specific radiation by ground-state atoms

Q2. Which light source is most commonly used in AAS for providing narrow element-specific lines?

• Deuterium lamp
• Tungsten-halogen lamp
• Hollow cathode lamp
• LED array

Correct Answer: Hollow cathode lamp

Q3. Which atomizer is preferred when the highest sensitivity and lowest detection limits (ppb) are required?

• Flame atomizer (air–acetylene)
• Graphite furnace atomizer
• Electrothermal nebulizer
• Hydride generator

Correct Answer: Graphite furnace atomizer

Q4. Which background correction technique uses a magnetic field to separate analyte absorption from background?

• Deuterium background correction
• Zeeman background correction
• Continuum source subtraction
• Matrix matching

Correct Answer: Zeeman background correction

Q5. Which of the following is NOT generally classified as an interference in AAS?

• Spectral overlap from other atomic lines
• Chemical formation of refractory compounds
• Variation in lamp current
• Instrumental drift from detector instability

Correct Answer: Variation in lamp current

Q6. Ionization interference in AAS most commonly occurs because:

• Atoms form molecules with the solvent
• Atoms are ionized at high atomizer temperatures, reducing neutral atom population
• Photons are scattered by droplets
• Matrix salts precipitate in the burner

Correct Answer: Atoms are ionized at high atomizer temperatures, reducing neutral atom population

Q7. What is the main role of a matrix modifier in graphite furnace AAS?

• Increase nebulizer efficiency
• Stabilize the analyte during pyrolysis and reduce losses
• Provide a continuum background for correction
• Simplify calibration by diluting the sample

Correct Answer: Stabilize the analyte during pyrolysis and reduce losses

Q8. Which detector is most commonly used in single-element AAS instruments?

• Photomultiplier tube
• Thermistor
• Mass spectrometer
• Charge-coupled device (CCD) array

Correct Answer: Photomultiplier tube

Q9. Selection of the analytical wavelength in AAS should generally use:

• A broad continuum to include neighboring lines
• The strongest resonance line of the analyte element
• A wavelength where solvent absorbs strongly
• The emission maxima of the flame

Correct Answer: The strongest resonance line of the analyte element

Q10. Compared with flame AAS, graphite furnace AAS typically provides:

• Higher sample throughput but worse sensitivity
• Lower detection limits and higher sensitivity
• Wider dynamic range but poorer precision
• Better suitability for volatile solvent analysis

Correct Answer: Lower detection limits and higher sensitivity

Q11. The primary function of a nebulizer in flame AAS is to:

• Burn the sample to ash
• Convert liquid sample into a fine aerosol
• Provide a source of excitation radiation
• Trap interfering ions

Correct Answer: Convert liquid sample into a fine aerosol

Q12. The limit of detection (LOD) in AAS is most strongly influenced by:

• The atomic mass of the element
• The signal-to-noise ratio of the measurement
• The color of the solution
• The sample container material

Correct Answer: The signal-to-noise ratio of the measurement

Q13. Which calibration approach is best for compensating significant matrix effects in sample analysis?

• External calibration with water-based standards
• Standard addition method
• Single-point calibration at zero
• Using only blanks for calibration

Correct Answer: Standard addition method

Q14. Which element is least commonly analyzed by conventional flame AAS in pharmaceutical quality control?

• Sodium (Na)
• Lead (Pb)
• Carbon (as organic carbon)
• Iron (Fe)

Correct Answer: Carbon (as organic carbon)

Q15. Which flame provides the highest temperature commonly used in flame AAS?

• Air–acetylene
• Nitrous oxide–acetylene
• Hydrogen–air
• Oxygen–methane

Correct Answer: Nitrous oxide–acetylene

Q16. A major advantage of hollow cathode lamps for AAS is:

• They produce a continuous broad spectrum
• They are element-specific and emit narrow resonance lines
• They eliminate all matrix interferences
• They act as both lamp and detector

Correct Answer: They are element-specific and emit narrow resonance lines

Q17. Which approach is suitable for correcting background absorption caused by molecular species in the flame?

• Increasing sample concentration
• Using background correction (deuterium lamp or Zeeman)
• Reducing the monochromator resolution
• Switching to UV–VIS spectroscopy

Correct Answer: Using background correction (deuterium lamp or Zeeman)

Q18. To minimize spectral interference from nearby atomic lines, one should use:

• A wider slit width on the monochromator
• A high-resolution monochromator or narrower slit
• A lower lamp current
• Untreated raw samples

Correct Answer: A high-resolution monochromator or narrower slit

Q19. Which strategy improves precision when sample introduction efficiency varies between runs?

• Standard addition
• Using an internal standard
• Relying on a single calibration point
• Changing the detector gain randomly

Correct Answer: Using an internal standard

Q20. Typical temperature program stages in graphite furnace AAS include:

• Ionization, recombination, emission
• Drying, pyrolysis (ash), atomization, and cleanout
• Condensation, nebulization, combustion
• Calibration, dilution, filtration

Correct Answer: Drying, pyrolysis (ash), atomization, and cleanout

Q21. According to Beer–Lambert behavior in AAS, absorbance is directly proportional to:

• The lamp age
• The concentration of the free ground‑state atoms (analyte concentration)
• The solvent boiling point
• The mass of the nebulizer

Correct Answer: The concentration of the free ground‑state atoms (analyte concentration)

Q22. Which instrument parameter most directly affects the degree of atomization and possible ionization of the analyte?

• Monochromator type
• Atomizer temperature
• Lamp diameter
• Sample vial color

Correct Answer: Atomizer temperature

Q23. A primary safety concern when operating flame AAS is:

• Generation of ionizing radiation
• Handling toxic liquid nitrogen
• Flammability and explosion risk from fuel gases like acetylene
• High-voltage static electricity only

Correct Answer: Flammability and explosion risk from fuel gases like acetylene

Q24. Spectral interference in AAS is best described as:

• Loss of sample during nebulization
• Overlap of absorption lines or background continuum from other species
• Electrical noise in the detector circuit
• Incorrect weighing of standards

Correct Answer: Overlap of absorption lines or background continuum from other species

Q25. Deuterium background correction in AAS works by:

• Providing element-specific resonance lines
• Supplying a continuous UV–VIS spectrum to measure and subtract background
• Magnetically splitting atomic lines
• Lowering the flame temperature

Correct Answer: Supplying a continuous UV–VIS spectrum to measure and subtract background

Q26. Which sample preparation technique is commonly necessary before AAS analysis of pharmaceutical solids?

• Direct injection without treatment
• Acid digestion (wet digestion) to convert matrix to aqueous solution
• Grinding and direct nebulization of powder
• Freeze-drying to remove water only

Correct Answer: Acid digestion (wet digestion) to convert matrix to aqueous solution

Q27. In AAS method validation, which parameter assesses reproducibility under the same conditions over a short time?

• Robustness
• Precision (repeatability)
• Specificity
• Accuracy

Correct Answer: Precision (repeatability)

Q28. Which factor will most likely reduce chemical interference from phosphate matrices when measuring a metal?

• Lowering the lamp current
• Adding a suitable releasing or protective agent (matrix modifier)
• Increasing the sample pH to extreme values
• Using wider slit widths

Correct Answer: Adding a suitable releasing or protective agent (matrix modifier)

Q29. Which statement about hydride generation in AAS is correct?

• It is used to analyze refractory metals like gold directly
• It enhances sensitivity for elements that form volatile hydrides (e.g., As, Se)
• It eliminates the need for any calibration
• It is identical to graphite furnace atomization

Correct Answer: It enhances sensitivity for elements that form volatile hydrides (e.g., As, Se)

Q30. For quality control in a pharmaceutical lab, which AAS practice helps ensure accuracy over long runs?

• Never running calibration checks after initial setup
• Frequent calibration checks, analysis of blanks and reference materials, and monitoring lamp condition
• Only analyzing samples and ignoring standards
• Changing atomizer type between each sample

Correct Answer: Frequent calibration checks, analysis of blanks and reference materials, and monitoring lamp condition

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com