Instrumentation of UV–Visible spectroscopy MCQs With Answer

Instrumentation of UV–Visible spectroscopy MCQs With Answer

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Instrumentation of UV–Visible Spectroscopy MCQs With Answer is designed to help M. Pharm students master the core hardware concepts behind UV–Vis analysis. This quiz focuses on the architecture and performance of spectrophotometers: light sources, monochromators, slit functions, spectral bandwidth, detectors, double- versus single-beam optics, cuvettes, accessories, and regulatory qualification. You will also test your knowledge of wavelength and photometric accuracy standards, stray light assessment, and factors that influence resolution and signal-to-noise. Each question is framed to reinforce practical decision-making in pharmaceutical analysis—choosing appropriate components, understanding their limits, and recognizing how instrument settings affect data quality. Use it as a rapid, high-yield revision tool before exams or laboratory method development.

Q1. In UV–Visible spectrophotometers, which source provides a continuous UV continuum approximately from 180 to 370 nm?

  • Tungsten–halogen lamp
  • Xenon flash lamp
  • Deuterium discharge lamp
  • Mercury low-pressure lamp

Correct Answer: Deuterium discharge lamp

Q2. The primary role of the monochromator in a UV–Vis spectrophotometer is to:

  • Increase lamp intensity at all wavelengths
  • Select a narrow band of wavelengths from a broad-spectrum source
  • Convert transmitted light into an electrical signal
  • Stabilize temperature of the sample compartment

Correct Answer: Select a narrow band of wavelengths from a broad-spectrum source

Q3. Increasing the slit width (spectral bandwidth) generally results in:

  • Higher resolution but lower signal-to-noise ratio
  • Lower resolution but higher signal-to-noise ratio
  • No change in resolution or signal-to-noise ratio
  • Elimination of stray light

Correct Answer: Lower resolution but higher signal-to-noise ratio

Q4. Which detector offers very high sensitivity and fast response in scanning UV–Vis spectrophotometers?

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

Correct Answer: Photomultiplier tube (PMT)

Q5. In a double-beam spectrophotometer, the main advantage over single-beam systems is that it:

  • Eliminates the need for a monochromator
  • Simultaneously measures sample and reference to compensate for source and detector drift
  • Removes the requirement for cuvettes
  • Eliminates baseline correction

Correct Answer: Simultaneously measures sample and reference to compensate for source and detector drift

Q6. For measurements in the deep UV region (e.g., 200–300 nm), the appropriate cuvette material is:

  • Standard soda-lime glass
  • Polycarbonate
  • Quartz (fused silica)
  • Polystyrene

Correct Answer: Quartz (fused silica)

Q7. Order-sorting filters used with diffraction grating monochromators are intended to:

  • Increase lamp intensity at short wavelengths
  • Reduce detector dark current
  • Block higher-order diffraction that would otherwise appear at λ/2, λ/3, etc.
  • Improve temperature control of the optical bench

Correct Answer: Block higher-order diffraction that would otherwise appear at λ/2, λ/3, etc.

Q8. Stray light in UV–Vis spectroscopy most commonly causes which analytical effect?

  • Apparent absorbance increases at high concentrations
  • Apparent absorbance decreases at high concentrations, limiting the measurable absorbance
  • No impact on absorbance accuracy
  • Wavelength shifts in peak maxima

Correct Answer: Apparent absorbance decreases at high concentrations, limiting the measurable absorbance

Q9. A widely used standard for wavelength accuracy verification in UV–Vis instruments is:

  • Potassium dichromate in 0.005 M sulfuric acid
  • Holmium oxide glass or solution
  • Toluene in hexane
  • Sodium iodide solution

Correct Answer: Holmium oxide glass or solution

Q10. Photometric (absorbance) accuracy in the UV region is commonly checked using:

  • Holmium oxide glass
  • Neutral density filters
  • Potassium dichromate in 0.005 M sulfuric acid
  • KCl solution

Correct Answer: Potassium dichromate in 0.005 M sulfuric acid

Q11. Which solution is commonly used as a cut-off to assess stray light around 200 nm in pharmacopeial qualification?

  • 1.2% w/v potassium chloride solution
  • 0.02% v/v toluene in hexane
  • Holmium perchlorate solution
  • 0.1 M sodium nitrite solution

Correct Answer: 1.2% w/v potassium chloride solution

Q12. In a typical scanning single-beam UV–Vis instrument, the correct optical sequence is:

  • Source → Sample → Monochromator → Detector
  • Source → Monochromator → Sample → Detector
  • Source → Filter → Detector → Sample
  • Source → Detector → Monochromator → Sample

Correct Answer: Source → Monochromator → Sample → Detector

Q13. The principal advantage of diode-array UV–Vis spectrophotometers is that they:

  • Eliminate the need for calibration
  • Acquire the entire spectrum simultaneously for rapid kinetics and profiling
  • Use PMTs to maximize dynamic range
  • Require no stray light control

Correct Answer: Acquire the entire spectrum simultaneously for rapid kinetics and profiling

Q14. The standard path length of most UV–Vis cuvettes used for quantitative analysis is:

  • 0.1 mm
  • 1 mm
  • 10 mm (1 cm)
  • 100 mm (10 cm)

Correct Answer: 10 mm (1 cm)

Q15. Which accessory is most appropriate for measuring diffuse reflectance spectra of powders or rough solids?

  • Attenuated total reflectance (ATR) crystal
  • Integrating sphere
  • Specular reflectance mirror at 45°
  • Flow-through cell

Correct Answer: Integrating sphere

Q16. Groove density of a diffraction grating primarily determines which monochromator property?

  • Polarization of output light
  • Angular dispersion and resolving power
  • Lamp warm-up time
  • Detector dark noise

Correct Answer: Angular dispersion and resolving power

Q17. To verify photometric linearity across a wide absorbance range, the most suitable tool is:

  • Neutral density filters with known transmittance
  • Holmium oxide glass
  • Deuterium lamp intensity monitor
  • Order-sorting filters

Correct Answer: Neutral density filters with known transmittance

Q18. A double monochromator design is preferred when the analytical method demands:

  • Higher stray light rejection and better peak purity
  • Faster full-spectrum acquisition
  • No need for slit width control
  • Operation without a detector

Correct Answer: Higher stray light rejection and better peak purity

Q19. Slowing the scan speed or increasing integration time during data acquisition will generally:

  • Decrease signal-to-noise but improve resolution
  • Increase signal-to-noise but may broaden effective bandwidth
  • Eliminate the need for baseline correction
  • Increase stray light

Correct Answer: Increase signal-to-noise but may broaden effective bandwidth

Q20. In diode-array UV–Vis instruments, the detector is typically a:

  • Photomultiplier tube (PMT)
  • Silicon photodiode array
  • Pyroelectric detector
  • Thermistor array

Correct Answer: Silicon photodiode array

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