HPLC detectors MCQs With Answer

HPLC detectors MCQs With Answer

This quiz set focuses on detectors used in High Performance Liquid Chromatography, tailored for M.Pharm students studying Advanced Instrumental Analysis (MPA 201T). It covers principles, detector types (UV/Vis, DAD/PDA, fluorescence, refractive index, ELSD, CAD, electrochemical, conductivity, and MS interfaces), practical considerations such as sensitivity, selectivity, gradient compatibility, flow cell effects, noise and limits of detection, and choices for non-chromophoric analytes. Each question is framed to deepen conceptual understanding and exam preparedness, with explanations implicit in carefully chosen answer options. Use these MCQs to reinforce detector selection and troubleshooting in pharmaceutical analysis.

Q1. Which fundamental law describes the relationship measured by a UV-Vis absorbance detector in HPLC?

• Transmittance is directly proportional to concentration
• Absorbance is proportional to concentration and path length (Beer–Lambert law)
• Scattering intensity is proportional to particle size
• Refractive index change is proportional to analyte mass

Correct Answer: Absorbance is proportional to concentration and path length (Beer–Lambert law)

Q2. What is the primary advantage of a diode array detector (DAD/PDA) over a single-wavelength UV detector?

• Higher baseline stability for non-volatile salts
• Simultaneous acquisition of full spectra across each chromatographic peak for peak purity analysis
• Greater sensitivity for non-chromophoric compounds
• Direct measurement of analyte mass

Correct Answer: Simultaneous acquisition of full spectra across each chromatographic peak for peak purity analysis

Q3. Which HPLC detector is universal for many analytes but incompatible with gradient elution because it is highly sensitive to mobile phase composition?

• Evaporative light scattering detector (ELSD)
• Photodiode array detector (DAD)
• Refractive index detector (RID)
• Mass spectrometer (MS)

Correct Answer: Refractive index detector (RID)

Q4. Which detector is described as mass-sensitive and provides a near-universal response suitable for gradient separations?

• Diode array detector (DAD)
• Charged aerosol detector (CAD)
• Refractive index detector (RID)
• Conductivity detector

Correct Answer: Charged aerosol detector (CAD)

Q5. Which detector typically requires a volatile mobile phase because the detection principle involves nebulization and evaporation of solvent?

• Refractive index detector (RID)
• Evaporative light scattering detector (ELSD)
• Diode array detector (DAD)
• Conductivity detector

Correct Answer: Evaporative light scattering detector (ELSD)

Q6. In a fluorescence detector for HPLC, which component converts emitted photons into an electrical signal with high gain?

• Thermocouple
• Photomultiplier tube (PMT)
• Refractive index cell
• Electrochemical electrode

Correct Answer: Photomultiplier tube (PMT)

Q7. Which detector provides wavelength-resolved spectra for each data point across a chromatographic peak, aiding identification?

• Diode array detector (DAD)/Photo diode array (PDA)
• Evaporative light scattering detector (ELSD)
• Refractive index detector (RID)
• Conductivity detector

Correct Answer: Diode array detector (DAD)/Photo diode array (PDA)

Q8. What type of electronic noise commonly dominates at low frequencies and can cause baseline drift in detectors?

• Shot noise
• Thermal (Johnson) noise
• Flicker noise (1/f noise)
• Quantization noise

Correct Answer: Flicker noise (1/f noise)

Q9. In chromatographic method validation, which signal-to-noise (S/N) ratio is typically used to define the limit of detection (LOD)?

• 1:1
• 3:1
• 5:1
• 10:1

Correct Answer: 3:1

Q10. Increasing the optical path length of a UV flow cell in HPLC will generally:

• Decrease sensitivity and decrease band broadening
• Increase sensitivity but also increase peak dispersion and potential band broadening
• Have no effect on sensitivity or peak shape
• Only affect noise without changing sensitivity

Correct Answer: Increase sensitivity but also increase peak dispersion and potential band broadening

Q11. Which detector measures changes in the refractive index (dielectric constant) of the eluent and is often used for sugars and polymers?

• Evaporative light scattering detector (ELSD)
• Refractive index detector (RID)
• Diode array detector (DAD)
• Mass spectrometer (MS)

Correct Answer: Refractive index detector (RID)

Q12. Which ionization technique is most suitable for ionizing polar, thermally labile biomolecules such as peptides in LC–MS?

• Electron impact ionization (EI)
• Electrospray ionization (ESI)
• Matrix-assisted laser desorption ionization (MALDI)
• Flame ionization

Correct Answer: Electrospray ionization (ESI)

Q13. In a diode array detector (PDA), which optical parameter primarily determines spectral resolution (optical bandwidth)?

• Flow cell volume
• Slit width or optical bandwidth
• Lamp current
• Detector thermostat temperature

Correct Answer: Slit width or optical bandwidth

Q14. Why is post-column derivatization commonly used for certain analytes in HPLC?

• To reduce retention time by changing polarity
• To convert non-chromophoric or non-fluorescent analytes into chromophores/fluorophores for detection
• To increase molecular weight for better MS detection
• To make the analyte volatile for ELSD

Correct Answer: To convert non-chromophoric or non-fluorescent analytes into chromophores/fluorophores for detection

Q15. Compared to ELSD, what is a typical advantage of the charged aerosol detector (CAD)?

• CAD requires non-volatile mobile phases while ELSD requires volatile ones
• CAD generally provides a more uniform response across different analytes (more consistent mass-based response)
• CAD is less compatible with gradient elution than ELSD
• CAD detects only chromophores

Correct Answer: CAD generally provides a more uniform response across different analytes (more consistent mass-based response)

Q16. Which detector type responds by measuring an electrochemical current produced by oxidation or reduction of analytes at an electrode?

• Fluorescence detector
• Electrochemical (amperometric/coulometric) detector
• Refractive index detector
• Diode array detector

Correct Answer: Electrochemical (amperometric/coulometric) detector

Q17. Which detector is specifically used to monitor ionic species by measuring the electrical conductivity of the eluent?

• Evaporative light scattering detector (ELSD)
• Conductivity detector
• Photodiode array detector (DAD)
• Mass spectrometer (MS)

Correct Answer: Conductivity detector

Q18. Which detector is best described as concentration-sensitive (signal proportional to analyte concentration rather than total mass reaching the detector)?

• Evaporative light scattering detector (ELSD)
• Charged aerosol detector (CAD)
• UV-Vis absorbance detector (DAD/PDA)
• Mass spectrometer (MS)

Correct Answer: UV-Vis absorbance detector (DAD/PDA)

Q19. How does reducing the internal volume of the detector flow cell generally affect chromatographic performance?

• Smaller flow cell volume increases peak dispersion and slows response time
• Smaller flow cell volume reduces peak broadening and gives a faster detector response
• Smaller flow cell volume eliminates baseline noise completely
• Smaller flow cell volume increases solvent consumption

Correct Answer: Smaller flow cell volume reduces peak broadening and gives a faster detector response

Q20. Which detector provides the highest specificity and can deliver structural (mass) information about analytes in HPLC?

• Diode array detector (DAD)
• Evaporative light scattering detector (ELSD)
• Refractive index detector (RID)
• Mass spectrometer (MS)

Correct Answer: Mass spectrometer (MS)

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