Principle of atomic absorption spectroscopy MCQs With Answer

Principle of Atomic Absorption Spectroscopy MCQs With Answer is designed for M.Pharm students to strengthen conceptual clarity and exam readiness in Modern Pharmaceutical Analytical Techniques. This set focuses on the core principles behind AAS—generation of free ground-state atoms, resonance line absorption, Beer–Lambert behavior, and the roles of sources, atomizers, and monochromators. You will also review background correction strategies, interferences and their remedies, flame and furnace parameters, and calibration approaches critical for reliable quantification in pharmaceutical matrices. Each question probes mechanistic understanding rather than rote facts, helping you connect instrument components to analytical performance, sensitivity, selectivity, and data quality. Use these MCQs to diagnose weak spots and master decision-making in real analytical scenarios.

Q1. What is the fundamental principle of Atomic Absorption Spectroscopy (AAS)?

• Excited atoms emit light proportional to concentration
• Ground-state atoms absorb element-specific radiation proportional to their concentration
• Molecules absorb broad-band radiation proportional to mass
• Ions scatter radiation inversely proportional to concentration

Correct Answer: Ground-state atoms absorb element-specific radiation proportional to their concentration

Q2. The primary light source used in line-source AAS is:

• Tungsten–halogen lamp
• Deuterium lamp
• Hollow cathode lamp with the analyte element in the cathode
• Mercury vapor lamp

Correct Answer: Hollow cathode lamp with the analyte element in the cathode

Q3. The main goal of atomization in AAS is to convert the sample into:

• Excited-state atoms
• Free ground-state atoms
• Stable molecular radicals
• Positive ions

Correct Answer: Free ground-state atoms

Q4. The monochromator in AAS primarily isolates which radiation from the source?

• Continuum background radiation
• Resonance line of the analyte
• Emission lines from the flame
• Second-order diffraction of the continuum

Correct Answer: Resonance line of the analyte

Q5. For elements forming refractory oxides (e.g., Al, Ti), which flame is preferred?

• Air–acetylene, lean
• Air–propane, stoichiometric
• Nitrous oxide–acetylene, fuel-rich
• Hydrogen–air, lean

Correct Answer: Nitrous oxide–acetylene, fuel-rich

Q6. The most common background correction method in flame AAS is:

• Zeeman effect with a magnetic field
• Deuterium lamp continuum correction
• Fourier transform filtering
• Electrothermal modulation

Correct Answer: Deuterium lamp continuum correction

Q7. Ionization interference in AAS can be minimized by:

• Adding an easily ionizable element such as potassium or cesium
• Cooling the flame to reduce Doppler broadening
• Using a wider slit width to pass more light
• Increasing lamp current beyond the rated value

Correct Answer: Adding an easily ionizable element such as potassium or cesium

Q8. The nebulizer and spray chamber primarily function to:

• Generate monatomic vapors directly from solids
• Produce a fine aerosol and remove large droplets before the flame
• Split emission lines via the Zeeman effect
• Convert ions back to atoms using a magnetic field

Correct Answer: Produce a fine aerosol and remove large droplets before the flame

Q9. For complex pharmaceutical matrices where matrix effects are significant, the preferred calibration approach is:

• External calibration with pure aqueous standards
• Standard addition to the sample
• Internal standardization with any convenient element
• Background subtraction without calibration

Correct Answer: Standard addition to the sample

Q10. Compared to flame AAS, graphite furnace AAS (GFAAS) provides:

• Lower sensitivity due to shorter residence time
• Higher detection limits and faster throughput
• Higher sensitivity due to longer atom residence time and effective path
• Less susceptibility to matrix effects

Correct Answer: Higher sensitivity due to longer atom residence time and effective path

Q11. A narrow line source is preferred in AAS because it:

• Eliminates the need for a monochromator entirely
• Minimizes spectral overlap and matches the atomic absorption profile
• Increases continuum background for better correction
• Reduces self-absorption in the flame

Correct Answer: Minimizes spectral overlap and matches the atomic absorption profile

Q12. The principal line-broadening mechanisms affecting atomic lines in flames are:

• Natural and power broadening
• Doppler and pressure (collisional) broadening
• Stark and Zeeman broadening
• Self-reversal and hyperfine broadening only

Correct Answer: Doppler and pressure (collisional) broadening

Q13. Deviation from Beer–Lambert law at higher analyte concentrations in AAS is often due to:

• Lamp aging increasing line intensity
• Self-absorption and stray light effects
• Reduced atomization efficiency at low temperatures
• Detector saturation only at low absorbance

Correct Answer: Self-absorption and stray light effects

Q14. Increasing the monochromator slit width in AAS generally:

• Improves spectral resolution but reduces signal
• Increases signal (throughput) but decreases spectral selectivity
• Reduces background and noise simultaneously
• Eliminates the need for background correction

Correct Answer: Increases signal (throughput) but decreases spectral selectivity

Q15. For element-specific emission in AAS, the cathode of a hollow cathode lamp is typically made of:

• An inert metal like platinum to avoid contamination
• The analyte element or an alloy containing it
• Aluminum for better sputtering efficiency
• Carbon to resist oxidation

Correct Answer: The analyte element or an alloy containing it

Q16. In GFAAS, matrix modifiers such as Pd/Mg(NO3)2 are used primarily to:

• Increase the atomization temperature above 3000 °C
• Stabilize the analyte during drying/ashing and reduce matrix losses
• Enhance Zeeman background splitting
• Convert molecular interferences into atomic emission

Correct Answer: Stabilize the analyte during drying/ashing and reduce matrix losses

Q17. Zeeman background correction in AAS relies on:

• Lamp intensity modulation with a deuterium source
• Magnetic splitting of atomic lines and differential measurement
• Self-reversal of hollow cathode emission lines
• Temperature cycling of the flame

Correct Answer: Magnetic splitting of atomic lines and differential measurement

Q18. For complex formulations in flame AAS, which statement is most appropriate?

• Internal standardization is routinely superior to standard addition
• Standard addition better compensates for matrix effects than internal standards
• No calibration is needed if background correction is applied
• Use external standards prepared in pure water only

Correct Answer: Standard addition better compensates for matrix effects than internal standards

Q19. The detector commonly used in AAS for UV–visible wavelengths is:

• Photomultiplier tube
• Thermocouple detector
• Bolometer
• Flame ionization detector

Correct Answer: Photomultiplier tube

Q20. To increase free-atom population for elements forming refractory oxides, an effective strategy is to:

• Use an oxidant-rich air–acetylene flame
• Use a fuel-rich nitrous oxide–acetylene flame
• Decrease lamp current to avoid saturation
• Replace hollow cathode with tungsten lamp

Correct Answer: Use a fuel-rich nitrous oxide–acetylene flame

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