Principle of flame emission spectroscopy MCQs With Answer

Principle of flame emission spectroscopy MCQs With Answer

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Principle of flame emission spectroscopy MCQs With Answer

Flame emission spectroscopy (also called flame photometry) is a foundational technique in Modern Pharmaceutical Analytical Techniques for quantifying alkali and alkaline earth metals in formulations and biological samples. It relies on thermal excitation of atoms in a flame, which emit characteristic radiation proportional to their concentration under controlled conditions. This quiz targets M. Pharm students, emphasizing core principles such as atomization, excitation, spectral isolation, interferences, and calibration strategies. You will explore flame chemistry, choice of fuel–oxidant systems, roles of releasing and ionization suppressors, and data handling approaches like standard addition and internal standards. The questions are designed to strengthen conceptual understanding and practical insight required for accurate, interference-free measurements.

Q1. The fundamental principle of flame emission spectroscopy (FES) is that

  • Thermally excited atoms in a flame emit characteristic radiation with intensity proportional to their concentration
  • Molecules in solution absorb UV radiation proportional to concentration (Beer–Lambert law)
  • Electrons emit radiation only when irradiated by an external lamp
  • Ions in plasma emit a continuum spectrum independent of concentration

Correct Answer: Thermally excited atoms in a flame emit characteristic radiation with intensity proportional to their concentration

Q2. In FES, the primary mechanism of excitation of analyte species is

  • Thermal excitation by the flame temperature
  • Optical excitation by an external radiation source
  • Chemiluminescence from reaction with oxidants
  • Electrothermal excitation by an applied electric field

Correct Answer: Thermal excitation by the flame temperature

Q3. The process that generates free neutral atoms from the aerosolized sample in the flame is best described as

  • Ionization
  • Dissociation
  • Atomization
  • Volatilization without decomposition

Correct Answer: Atomization

Q4. Flame emission spectroscopy is especially suited for quantitative determination of

  • Alkali and alkaline earth metals
  • Heavy transition metals with complex spectra
  • Lanthanides in trace levels
  • Nonmetals such as sulfur and phosphorus

Correct Answer: Alkali and alkaline earth metals

Q5. Unlike atomic absorption spectroscopy, FES does not require an external radiation source because

  • The flame provides a continuous UV source
  • The analyte atoms themselves emit characteristic radiation after thermal excitation
  • The detector generates its own excitation spectrum
  • Background emission is sufficient for line selection

Correct Answer: The analyte atoms themselves emit characteristic radiation after thermal excitation

Q6. The principal function of the nebulizer–burner system in FES is to

  • Filter out unwanted spectral lines
  • Convert the liquid sample into a fine aerosol and deliver it to a stable flame
  • Cool the sample to prevent ionization
  • Generate monochromatic radiation for excitation

Correct Answer: Convert the liquid sample into a fine aerosol and deliver it to a stable flame

Q7. Using a hotter N2O–acetylene flame instead of an air–acetylene flame primarily helps to

  • Increase solvent evaporation time and reduce signal
  • Reduce chemical interferences from refractory compound formation
  • Enhance ionization of alkali metals
  • Eliminate the need for spectral isolation

Correct Answer: Reduce chemical interferences from refractory compound formation

Q8. Ionization interference in FES can be minimized by adding an ionization suppressor such as KCl or CsCl because it

  • Promotes formation of volatile analyte complexes
  • Shifts the ionization equilibrium toward neutral atoms by providing an excess of easily ionized species
  • Increases the viscosity of the solution, improving nebulization
  • Blocks the detector from excess photons

Correct Answer: Shifts the ionization equilibrium toward neutral atoms by providing an excess of easily ionized species

Q9. A common strategy to mitigate phosphate interference in Ca or Mg determination by FES is to add La3+ because it

  • Acts as an internal standard with identical wavelength
  • Forms refractory oxides that reduce background
  • Acts as a releasing/protective agent to prevent formation of nonvolatile Ca/Mg phosphates
  • Increases flame temperature

Correct Answer: Acts as a releasing/protective agent to prevent formation of nonvolatile Ca/Mg phosphates

Q10. The region of the flame typically observed for analytical emission in FES is

  • The fuel-rich inner cone where combustion begins
  • The interconal region just above the primary reaction zone
  • The outer cone tip only
  • The preheating zone below the burner slot

Correct Answer: The interconal region just above the primary reaction zone

Q11. In basic flame photometers, spectral isolation of the analytical line is most commonly achieved using

  • Prism monochromators with high dispersion
  • Grating monochromators with high resolution
  • Interference filters centered on the analyte wavelength
  • Fabry–Pérot etalons

Correct Answer: Interference filters centered on the analyte wavelength

Q12. When matrix effects are significant and sample volume is limited, the preferred calibration approach in FES is

  • External calibration with solvent-matched standards only
  • Standard addition directly to the sample
  • Use of a universal calibration factor
  • Background correction by blank subtraction alone

Correct Answer: Standard addition directly to the sample

Q13. At higher analyte concentrations, self-absorption in the flame often causes

  • Perfect linearity over the entire range
  • Positive curvature (superlinear response)
  • Negative curvature (sublinear response) of the calibration curve
  • No change in response but increased baseline noise

Correct Answer: Negative curvature (sublinear response) of the calibration curve

Q14. The most common photodetector used in flame emission spectrometers due to its sensitivity and fast response is

  • Silicon photodiode array
  • Photomultiplier tube (PMT)
  • Thermocouple detector
  • Bolometer

Correct Answer: Photomultiplier tube (PMT)

Q15. The dependence of excited-state population on flame temperature in FES is described by the

  • Beer–Lambert law
  • Planck radiation law
  • Boltzmann distribution
  • Rayleigh scattering law

Correct Answer: Boltzmann distribution

Q16. Among the following fuel–oxidant combinations, the one providing the higher flame temperature for difficult-to-atomize species is

  • Air–acetylene
  • N2O–acetylene
  • Air–hydrogen
  • O2–propane

Correct Answer: N2O–acetylene

Q17. A suitable internal standard for FES should

  • Be present endogenously in the sample at high concentration
  • Have an emission line close to the analyte and similar excitation characteristics but be absent from the sample
  • Emit a broad continuum to average matrix effects
  • Have a much higher ionization potential than the analyte

Correct Answer: Have an emission line close to the analyte and similar excitation characteristics but be absent from the sample

Q18. A practical approach to correct for background emission and flame luminosity in FES is

  • Increasing slit width to capture more signal
  • Using a blank matrix and subtracting its signal from sample measurements
  • Operating at the lowest possible flame temperature
  • Eliminating any optical filter

Correct Answer: Using a blank matrix and subtracting its signal from sample measurements

Q19. Which statement best reflects the comparative capability of FES?

  • FES is generally most sensitive and selective for alkali/alkaline earth metals; AAS is often superior for many other metals
  • FES requires a hollow cathode lamp to achieve sensitivity
  • FES is preferred for nonmetals due to strong emission
  • FES has no susceptibility to chemical or ionization interferences

Correct Answer: FES is generally most sensitive and selective for alkali/alkaline earth metals; AAS is often superior for many other metals

Q20. Nebulization efficiency in FES will typically decrease when the sample

  • Has lower surface tension and lower viscosity
  • Is diluted with ethanol to reduce droplet size
  • Has high viscosity, producing larger droplets and coarser aerosols
  • Is filtered through 0.2 µm membranes

Correct Answer: Has high viscosity, producing larger droplets and coarser aerosols

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