Instrumentation of UV–Visible spectrophotometer MCQs With Answer

Instrumentation of UV–Visible spectrophotometer MCQs With Answer — This concise introduction helps B.Pharm students master UV–Visible spectrophotometer instrumentation fundamentals. Topics include light sources (deuterium, tungsten-halogen), monochromators (diffraction grating, prism), slits, spectral bandwidth (SBW), detectors (photomultiplier tube, photodiode array), and accessories (quartz cuvettes, integrating sphere). Emphasis is placed on operational parameters: wavelength and photometric accuracy, stray light, noise and signal-to-noise ratio, baseline correction, calibration, Beer’s law, detection limits, linearity, sample preparation, and routine maintenance for pharmaceutical analysis. Clear, practical focus readies you for lab work, QC, and exam questions. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which light source is most commonly used for accurate measurements in the UV region (190–400 nm)?

• Wavelength-stabilized tungsten lamp
• Deuterium lamp
• Halogen lamp
• LED

Correct Answer: Deuterium lamp

Q2. Which lamp is typically used for measurements in the visible region (400–700 nm)?

• Deuterium lamp
• Tungsten-halogen lamp
• Photomultiplier tube

Correct Answer: Tungsten-halogen lamp

Q3. What dispersive element is most commonly used in modern monochromators for UV–Vis instruments?

• Prism
• Diffraction grating
• Interference filter
• Polarizer

Correct Answer: Diffraction grating

Q4. What is the primary function of the monochromator in a UV–Vis spectrophotometer?

• Convert light to electrical signal
• Isolate a narrow band of wavelengths
• Increase lamp intensity
• Stabilize temperature

Correct Answer: Isolate a narrow band of wavelengths

Q5. Spectral bandwidth (SBW) is best described as:

• The intensity of the light source
• The full width at half maximum (FWHM) of the transmitted wavelength band
• The pathlength of the cuvette
• The detector response time

Correct Answer: The full width at half maximum (FWHM) of the transmitted wavelength band

Q6. Which detector provides very high sensitivity for low-light UV measurements?

• CCD array
• Photodiode array
• Thermopile
• Photomultiplier tube (PMT)

Correct Answer: Photomultiplier tube (PMT)

Q7. A key advantage of a double-beam spectrophotometer over a single-beam design is:

• Lower cost
• Simultaneous reference and sample measurement to reduce drift
• Higher stray light
• No need for calibration

Correct Answer: Simultaneous reference and sample measurement to reduce drift

Q8. According to the Beer–Lambert law, absorbance is directly proportional to which factors?

• Wavelength and detector type
• Concentration, pathlength, and molar absorptivity
• Lamp intensity and slit width
• Temperature only

Correct Answer: Concentration, pathlength, and molar absorptivity

Q9. What is the main effect of stray light on high-absorbance measurements?

• It increases the measured absorbance
• It has no effect
• It causes measured absorbance to be lower than true value, causing deviation from Beer’s law
• It changes the cuvette pathlength

Correct Answer: It causes measured absorbance to be lower than true value, causing deviation from Beer’s law

Q10. Which material is commonly used as a wavelength calibration standard for UV–Vis instruments?

• Holmium oxide glass
• Sodium chloride solution
• Potassium bromide pellet
• Calcium carbonate powder

Correct Answer: Holmium oxide glass

Q11. What is the standard cuvette pathlength used in most UV–Vis quantitative measurements?

• 0.1 cm
• 0.5 cm
• 1 cm
• 10 cm

Correct Answer: 1 cm

Q12. Which mathematical relationship correctly converts transmittance (T) to absorbance (A)?

• A = log10(T)
• A = -log10(T)
• A = T/100
• A = 10^T

Correct Answer: A = -log10(T)

Q13. Increasing the scan speed of a spectrophotometer generally results in:

• Improved resolution and lower noise
• Lower noise and higher signal
• Increased noise and potentially lower resolution
• No change in measurement quality

Correct Answer: Increased noise and potentially lower resolution

Q14. Baseline correction in UV–Vis measurement is performed to:

• Remove solvent and instrument contributions to the signal
• Increase lamp intensity
• Change cuvette pathlength
• Adjust detector sensitivity

Correct Answer: Remove solvent and instrument contributions to the signal

Q15. Which standard is commonly used to check photometric accuracy in the UV region?

• Potassium dichromate solution
• Sodium chloride solution
• Holmium oxide glass for photometric only
• Distilled water

Correct Answer: Potassium dichromate solution

Q16. Noise in UV–Vis measurements is commonly expressed as:

• Wavelength accuracy
• Signal-to-noise ratio (S/N)
• Pathlength
• Spectral bandwidth

Correct Answer: Signal-to-noise ratio (S/N)

Q17. Which factors primarily determine the spectral resolution of a UV–Vis spectrophotometer?

• Detector material only
• Monochromator slit width and grating/prism design
• Type of solvent used
• Sample concentration

Correct Answer: Monochromator slit width and grating/prism design

Q18. A major advantage of a photodiode array (PDA) detector is:

• Very high single-wavelength sensitivity compared to PMT
• Simultaneous acquisition of multiple wavelengths for fast scanning
• Lower cost but much slower scans
• Unlimited dynamic range

Correct Answer: Simultaneous acquisition of multiple wavelengths for fast scanning

Q19. The purpose of a chopper and lock-in amplifier in a spectrophotometer is to:

• Increase stray light
• Provide synchronous detection to improve signal-to-noise
• Adjust cuvette pathlength electronically
• Measure temperature of the sample

Correct Answer: Provide synchronous detection to improve signal-to-noise

Q20. When selecting a solvent for UV–Vis analysis, the solvent should be:

• Opaque at the measurement wavelength
• Transparent in the wavelength range of interest
• Highly colored to increase signal
• Reactive with the analyte

Correct Answer: Transparent in the wavelength range of interest

Q21. The typical useful photometric absorbance range for many UV–Vis instruments is:

• 0–0.1 AU
• 0–0.5 AU
• 0–2 AU
• 0–10 AU

Correct Answer: 0–2 AU

Q22. Which material is commonly used to verify wavelength accuracy of a UV–Vis spectrophotometer?

• Neutral density filter
• Holmium oxide filter
• Distilled water
• Polystyrene film

Correct Answer: Holmium oxide filter

Q23. How does reducing the spectral bandwidth affect measurements?

• Increases signal intensity and decreases resolution
• Decreases resolution and increases noise
• Narrows the wavelength range passed, increasing resolution but reducing signal intensity
• Has no effect on measurements

Correct Answer: Narrows the wavelength range passed, increasing resolution but reducing signal intensity

Q24. An integrating sphere accessory is used to measure samples that:

• Are perfectly transparent only
• Scatter or reflect light (diffuse samples)
• Have very low concentration only
• Require heating

Correct Answer: Scatter or reflect light (diffuse samples)

Q25. Why are quartz cuvettes preferred for many UV measurements?

• They are cheaper than glass
• They are transparent down to ~190 nm and chemically resistant
• They have a larger pathlength by default
• They absorb strongly in the UV

Correct Answer: They are transparent down to ~190 nm and chemically resistant

Q26. Common sources of photometric noise include:

• Lamp fluctuations, electronic noise, and stray light
• Only sample concentration
• Only cuvette material
• Only room lighting

Correct Answer: Lamp fluctuations, electronic noise, and stray light

Q27. Which tool is commonly used to check photometric linearity and instrument response across absorbance levels?

• Holmium oxide filter
• Neutral density filters
• Quartz cuvettes of different pathlengths only
• Distilled water

Correct Answer: Neutral density filters

Q28. Why is detector linearity important in quantitative UV–Vis analysis?

• It ensures the detector does not overheat
• It ensures measured signal is proportional to incident light intensity so absorbance correlates with concentration
• It reduces cuvette breakage
• It determines the lamp lifetime

Correct Answer: It ensures measured signal is proportional to incident light intensity so absorbance correlates with concentration

Q29. In which units is spectral bandwidth (SBW) usually expressed?

• Watts
• Nanometers (nm)
• Absorbance units (AU)
• Seconds

Correct Answer: Nanometers (nm)

Q30. In a single-beam spectrophotometer, what step is essential before measuring sample absorbance?

• Increase lamp voltage to maximum
• Record a blank or reference measurement
• Switch to double-beam mode
• Remove the monochromator

Correct Answer: Record a blank or reference measurement

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