Polarography is a sensitive electroanalytical method widely applied in pharmaceutical analysis for trace metal and drug determinations. Using a renewable mercury electrode and current–potential curves, polarographic analysis provides both qualitative identification (via half-wave or peak potentials) and quantitative assays (via diffusion or stripping currents). Key applications include assay of reducible drugs, impurity profiling, stability testing, formulation analysis, and environmental monitoring of pharmaceutical residues. Mastery of concepts such as the Ilkovic equation, supporting electrolytes, deoxygenation, adsorptive and stripping variants, and electrode selection helps B.Pharm students apply polarography effectively in laboratory and regulatory settings. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary measurable signal in classical polarography?
- Change in solution color
- Current as a function of applied potential at a dropping mercury electrode
- Mass loss of the electrode
- Temperature variation of the solution
Correct Answer: Current as a function of applied potential at a dropping mercury electrode
Q2. The Ilkovic equation in polarography relates the diffusion current primarily to which factor?
- Solution pH only
- Concentration of electroactive species, diffusion coefficient and drop parameters
- Optical absorbance of the analyte
- Ambient temperature only
Correct Answer: Concentration of electroactive species, diffusion coefficient and drop parameters
Q3. Which is a key analytical advantage of polarography in pharmaceutical analysis?
- Requires no supporting electrolyte
- High sensitivity for trace metal and reducible organic species
- Insensitive to dissolved oxygen
- Universal applicability to all drug types without sample prep
Correct Answer: High sensitivity for trace metal and reducible organic species
Q4. What does DME stand for in polarographic techniques?
- Diffusion measurement electrode
- Dropping mercury electrode
- Dynamic mass electrode
- Direct measurement electrode
Correct Answer: Dropping mercury electrode
Q5. Which polarographic technique involves a preconcentration step on the electrode followed by a stripping analysis?
- Classical DC polarography
- Stripping voltammetry
- Potentiometric titration
- UV-visible spectrophotometry
Correct Answer: Stripping voltammetry
Q6. A common interference in polarographic measurements that increases background current is:
- Dissolved oxygen
- Low ionic strength of supporting electrolyte
- High optical turbidity
- Ambient light
Correct Answer: Dissolved oxygen
Q7. Which functional group in drugs is most readily analyzed by reductive polarography?
- Alkyl chains
- Nitro groups
- Nonpolar aromatic rings with no substituents
- Quaternary ammonium salts
Correct Answer: Nitro groups
Q8. Which parameter of the dropping mercury electrode appears explicitly in the Ilkovic equation?
- Optical reflectivity of the drop
- Drop time (and drop size/flow rate)
- Electrode color
- Magnetic susceptibility
Correct Answer: Drop time (and drop size/flow rate)
Q9. The primary purpose of adding a supporting electrolyte in polarographic analysis is to:
- Increase the solubility of gases
- Maintain ionic strength and minimize migration effects
- Provide a visual color change
- React chemically with the analyte to form a complex
Correct Answer: Maintain ionic strength and minimize migration effects
Q10. Adsorptive stripping polarography is particularly useful for analytes that:
- Are volatile and nonadsorbing
- Strongly adsorb onto the electrode surface
- Have no redox activity
- Are gaseous at room temperature
Correct Answer: Strongly adsorb onto the electrode surface
Q11. Why are mercury electrodes favored in many polarographic analyses?
- They are inexpensive and non-toxic
- They provide a renewable, reproducible surface and a wide cathodic potential range
- They are ideal for high-temperature assays
- They emit visible light to aid detection
Correct Answer: They provide a renewable, reproducible surface and a wide cathodic potential range
Q12. A typical diffusion-controlled polarographic response appears as which shape on the polarogram?
- Sharp symmetric peak like in chromatography
- Sigmoidal wave approaching a limiting current
- Random noise with no distinct feature
- Sine wave
Correct Answer: Sigmoidal wave approaching a limiting current
Q13. Which sample pretreatment step is commonly required before polarographic measurement?
- Removal of supporting electrolyte
- Deoxygenation by purging with nitrogen or argon
- Addition of organic dyes
- Heating to boiling point
Correct Answer: Deoxygenation by purging with nitrogen or argon
Q14. Which polarographic variant typically offers improved sensitivity and resolution compared with DC polarography?
- Differential pulse polarography (DPP)
- Simple potentiometry
- Gravimetric titration
- Conventional UV spectrophotometry
Correct Answer: Differential pulse polarography (DPP)
Q15. One analytical limitation of polarography in complex pharmaceutical matrices is:
- Complete lack of sensitivity
- Adsorption and matrix interferences from surfactants, proteins or excipients
- Inability to measure metals
- Requirement for extremely large sample volumes only
Correct Answer: Adsorption and matrix interferences from surfactants, proteins or excipients
Q16. The half-wave potential (E1/2) in polarography is most useful for:
- Quantifying the mass of electrode used
- Qualitative identification of the electroactive species
- Measuring solution viscosity
- Determining pH directly
Correct Answer: Qualitative identification of the electroactive species
Q17. To lower the detection limit for trace analytes in polarography, the recommended approach is to:
- Decrease deposition/preconcentration time
- Use preconcentration techniques such as adsorptive or stripping methods
- Remove the supporting electrolyte entirely
- Use visible light irradiation during measurement
Correct Answer: Use preconcentration techniques such as adsorptive or stripping methods
Q18. Which operational factor primarily controls the drop time in a classical dropping mercury electrode?
- Ambient room color
- Mercury flow rate and capillary geometry
- Analyst’s hand temperature
- Magnetic stirring speed only
Correct Answer: Mercury flow rate and capillary geometry
Q19. In classical polarography, the steady or limiting current due to mass transport is called the:
- Migration current
- Diffusion (limiting) current
- Coulometric current
- Photocurrent
Correct Answer: Diffusion (limiting) current
Q20. A reversible electrode reaction in polarography is typically indicated by:
- A completely flat baseline
- A well-defined half-wave potential and reproducible wave shape independent of scan direction
- A large hysteresis between forward and reverse scans
- No measurable current
Correct Answer: A well-defined half-wave potential and reproducible wave shape independent of scan direction
Q21. Which heavy metal commonly determined by polarography in pharmaceutical or environmental samples is:
- Lead (Pb)
- Carbon
- Silicon (as major component)
- Nitrogen gas
Correct Answer: Lead (Pb)
Q22. A major practical disadvantage of mercury electrodes that affects modern lab use is:
- High electrical resistance
- Toxicity and environmental disposal concerns
- Inability to measure cathodic processes
- Excessive cost compared to platinum
Correct Answer: Toxicity and environmental disposal concerns
Q23. Stripping voltammetry consists of which two main operational stages?
- Filtration followed by centrifugation
- Deposition (preconcentration) on the electrode, followed by stripping (measurement)
- Neutralization and titration
- Evaporation and crystallization
Correct Answer: Deposition (preconcentration) on the electrode, followed by stripping (measurement)
Q24. In anodic stripping voltammetry the analytical peak current is directly related to:
- Wavelength of incident light
- Amount of analyte preconcentrated on the electrode (concentration × deposition time)
- Sample color only
- Magnetic properties of the analyte
Correct Answer: Amount of analyte preconcentrated on the electrode (concentration × deposition time)
Q25. Which electrochemical parameter is most diagnostic for identifying an unknown electroactive impurity in a drug by polarography?
- Solution viscosity
- Half-wave potential (E1/2)
- Boiling point of the solvent
- Ambient humidity
Correct Answer: Half-wave potential (E1/2)
Q26. Compared to the classical dropping mercury electrode, a hanging mercury drop electrode (HMDE) offers:
- Worse reproducibility and larger drop waste
- Better reproducibility, controlled drop size and lower sample consumption
- Inability to form mercury drops
- No advantage at all
Correct Answer: Better reproducibility, controlled drop size and lower sample consumption
Q27. Which change in experimental conditions generally increases the sensitivity in adsorptive stripping polarography?
- Reducing adsorption time to zero
- Increasing adsorption or deposition time
- Removing the supporting electrolyte
- Operating at very high temperatures only
Correct Answer: Increasing adsorption or deposition time
Q28. With appropriate preconcentration (stripping) techniques, polarographic detection limits for metal ions can commonly reach which level?
- Percent level (>1%)
- Parts-per-billion (ppb, μg·L−1) or sub-ppb in favorable cases
- Only gram-per-liter
- Megagram quantities
Correct Answer: Parts-per-billion (ppb, μg·L−1) or sub-ppb in favorable cases
Q29. A polarogram graphically represents which relationship?
- Absorbance vs wavelength
- Current vs applied potential
- Mass vs time
- Temperature vs concentration
Correct Answer: Current vs applied potential
Q30. In pharmaceutical stability studies polarography can help by:
- Determining the melting point of excipients
- Detecting redox-active degradation products and monitoring impurity formation
- Measuring viscosity of syrups
- Replacing all microbiological assays
Correct Answer: Detecting redox-active degradation products and monitoring impurity formation
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.
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