Calibration procedure for pH meter MCQs With Answer is an essential study area for B.Pharm students focusing on accurate pH measurement in pharmaceutical analysis. This introduction covers buffer selection (pH 4.01, 7.00, 10.01), electrode conditioning, two‑ and three‑point calibration, temperature compensation, Nernst slope, offset, and documentation per SOP and regulatory requirements. Understanding electrode maintenance, storage solutions, ionic strength adjusters (ISA), and troubleshooting (drift, fouling, junction errors) improves assay accuracy, precision, and traceability. Hands‑on calibration skills ensure reliable dissolution testing, formulation development, and QC release. Employing correct calibration ensures compliance with pharmacopeial standards and data integrity during release testing. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary purpose of performing a calibration procedure for a pH meter?
- To sterilize the electrode before use
- To ensure accuracy and traceability of pH measurements
- To change the electrode internal solution
- To measure conductivity of the sample
Correct Answer: To ensure accuracy and traceability of pH measurements
Q2. Which set of standard buffer pH values is most commonly used for three‑point pH meter calibration?
- pH 1.00, 4.00, 7.00
- pH 4.01, 7.00, 10.01
- pH 3.00, 6.00, 9.00
- pH 2.00, 5.00, 8.00
Correct Answer: pH 4.01, 7.00, 10.01
Q3. Why is a three‑point calibration preferred over two‑point calibration when analyzing samples across a wide pH range?
- It shortens electrode life
- It verifies electrode linearity and accuracy across the entire range
- It avoids the need for temperature compensation
- It reduces buffer consumption
Correct Answer: It verifies electrode linearity and accuracy across the entire range
Q4. What is the correct first step when starting a pH meter calibration?
- Immerse electrode directly into the sample
- Rinse the electrode with distilled or deionized water and blot dry
- Soak electrode in concentrated acid
- Replace the meter battery
Correct Answer: Rinse the electrode with distilled or deionized water and blot dry
Q5. What does automatic temperature compensation (ATC) do during pH measurement?
- Automatically adjusts the pH meter display to account for temperature effects on electrode response
- Keeps the buffer solutions at 25 °C
- Prevents electrode fouling
- Measures conductivity of the sample
Correct Answer: Automatically adjusts the pH meter display to account for temperature effects on electrode response
Q6. What is the theoretical Nernst slope in mV per pH unit at 25 °C for a perfect glass electrode?
- 25.7 mV/pH
- 59.16 mV/pH
- 100 mV/pH
- 7.00 mV/pH
Correct Answer: 59.16 mV/pH
Q7. Which practice helps maintain buffer integrity and accurate calibration?
- Using the same buffer repeatedly without checking expiration
- Preparing buffers from random tap water
- Using fresh, traceable commercial buffer solutions and avoiding contamination
- Heating buffers to speed calibration
Correct Answer: Using fresh, traceable commercial buffer solutions and avoiding contamination
Q8. How should a glass pH electrode be stored between uses to preserve performance?
- Stored dry on the bench
- Stored in electrode storage solution or appropriate KCl solution
- Stored in concentrated sodium hydroxide
- Frozen for long‑term storage
Correct Answer: Stored in electrode storage solution or appropriate KCl solution
Q9. What is the definition of electrode response time in pH measurement?
- Time taken for meter battery to charge
- Time required for the electrode potential to stabilize within an acceptable range after immersion
- Duration of the calibration procedure
- Time between buffer preparations
Correct Answer: Time required for the electrode potential to stabilize within an acceptable range after immersion
Q10. Which electrode symptom most likely indicates a clogged or contaminated reference junction?
- Faster than normal response
- Large, unstable offset and erratic drift
- Perfect slope and no offset
- Continuous increase in buffer pH
Correct Answer: Large, unstable offset and erratic drift
Q11. Which components are essential parts of a typical pH measuring system?
- Glass measuring electrode, reference electrode, meter electronics, temperature probe
- Only a conductivity cell and a pump
- Chromatography column and detector
- Mass spectrometer and vacuum pump
Correct Answer: Glass measuring electrode, reference electrode, meter electronics, temperature probe
Q12. What effect does a large difference in ionic strength between calibration buffers and sample cause?
- No measurable effect on pH
- Liquid junction potential variations leading to systematic error
- Instant electrode regeneration
- Faster calibration
Correct Answer: Liquid junction potential variations leading to systematic error
Q13. What is the role of an ionic strength adjuster (ISA) when measuring pH?
- To change the electrode slope
- To stabilize ionic strength and minimize junction potential errors in samples of varying ionic strength
- To sterilize the sample
- To act as a buffer at pH 7 only
Correct Answer: To stabilize ionic strength and minimize junction potential errors in samples of varying ionic strength
Q14. When is single‑point calibration acceptable for routine pH monitoring?
- When strict regulatory accuracy across a wide range is required
- When measurements are consistently near a known pH and high precision is not critical
- When performing final QC release testing
- When replacing the electrode
Correct Answer: When measurements are consistently near a known pH and high precision is not critical
Q15. What does the electrode slope value indicate after calibration?
- The electrical resistance of the meter
- The sensitivity in mV change per pH unit and closeness to the Nernst response
- The temperature of the buffer
- The volume of buffer used
Correct Answer: The sensitivity in mV change per pH unit and closeness to the Nernst response
Q16. After completing calibration, what is an important verification step?
- Discard the meter and buy a new one
- Check a third buffer (not used for calibration) to verify accuracy
- Immediately immerse electrode in bleach
- Store the electrode dry
Correct Answer: Check a third buffer (not used for calibration) to verify accuracy
Q17. What documentation entries should be recorded in the calibration log per SOP?
- Date, buffers used, measured slope/offset, temperature, technician signature
- Only the technician name
- The brand of buffer only
- Meter color and bench location
Correct Answer: Date, buffers used, measured slope/offset, temperature, technician signature
Q18. Which cleaning procedure is appropriate for a glass electrode fouled with organic residues?
- Wipe with dry tissue only
- Soak in an appropriate cleaning solution (mild detergent or specific electrode cleaner) then rinse
- Immerse permanently in concentrated acid
- Heat electrode in a flame
Correct Answer: Soak in an appropriate cleaning solution (mild detergent or specific electrode cleaner) then rinse
Q19. How can you check pH meter performance between routine calibrations?
- Use a blank distilled water sample as the only check
- Measure a control buffer or standard solution and compare to known value
- Only read the meter display without a sample
- Shake the electrode vigorously
Correct Answer: Measure a control buffer or standard solution and compare to known value
Q20. How does temperature influence the pH electrode slope and calibration?
- Slope is independent of temperature
- Slope follows the Nernst equation and increases with temperature; calibration must account for temperature
- Temperature only affects conductivity, not pH
- Calibration should always be performed at 0 °C
Correct Answer: Slope follows the Nernst equation and increases with temperature; calibration must account for temperature
Q21. Why is frequent recalibration necessary in pharmaceutical QC environments?
- To comply with pharmacopeial standards, ensure traceability, and maintain measurement integrity
- To increase electrode wear intentionally
- To avoid recording any documentation
- Because buffers degrade instantly after opening
Correct Answer: To comply with pharmacopeial standards, ensure traceability, and maintain measurement integrity
Q22. What is the recommended approach when calibrating for measurements at a temperature significantly different from 25 °C?
- Ignore temperature and calibrate at room temperature
- Perform calibration at the sample temperature or use accurate ATC during calibration
- Use only pH 7 buffer regardless of temperature
- Double the number of calibration points without temperature correction
Correct Answer: Perform calibration at the sample temperature or use accurate ATC during calibration
Q23. Which observation suggests the electrode may be reaching end of useful life?
- Stable slope at theoretical Nernst value and fast response
- Slow response, persistent inaccurate slope, and frequent drift despite cleaning
- Perfect performance with no maintenance
- Electrode glowing under UV light
Correct Answer: Slow response, persistent inaccurate slope, and frequent drift despite cleaning
Q24. If significant drift is observed during a measurement session, what is the best immediate action?
- Continue measurements and ignore drift
- Recheck calibration, clean or recondition the electrode, and repeat calibration if needed
- Shake the meter vigorously
- Replace sample with distilled water
Correct Answer: Recheck calibration, clean or recondition the electrode, and repeat calibration if needed
Q25. What is the effect of proteinaceous or oily sample matrices on glass pH electrodes?
- They improve electrode slope
- They foul the glass membrane and junction, causing slow response and inaccurate readings
- They sterilize the electrode
- They reduce the need for calibration
Correct Answer: They foul the glass membrane and junction, causing slow response and inaccurate readings
Q26. Which buffer should be used to verify accuracy after a two‑point calibration using pH 4.01 and 7.00 buffers?
- pH 4.01 again
- pH 7.00 again
- A third check buffer such as pH 10.01 to confirm performance across the range
- Distilled water
Correct Answer: A third check buffer such as pH 10.01 to confirm performance across the range
Q27. What is the correct sequence when performing a two‑point calibration on a pH meter?
- Immerse in first buffer, record stable reading, rinse, immerse in second buffer, record stable reading, save calibration
- Turn off meter, dry electrode, record nothing
- Mix buffers together, immerse electrode, record result
- Calibrate using only distilled water
Correct Answer: Immerse in first buffer, record stable reading, rinse, immerse in second buffer, record stable reading, save calibration
Q28. What is the primary function of the reference electrode in a pH electrode assembly?
- To change the sample pH
- To provide a stable reference potential against which the measuring electrode potential is compared
- To heat the solution
- To measure ionic strength directly
Correct Answer: To provide a stable reference potential against which the measuring electrode potential is compared
Q29. How should an electrode be handled after measuring organic solvent samples to prevent damage?
- Rinse thoroughly with an appropriate solvent, then with distilled water, and store per SOP
- Wipe with paper towel only
- Instantly store dry at room temperature
- Immerse in concentrated acid
Correct Answer: Rinse thoroughly with an appropriate solvent, then with distilled water, and store per SOP
Q30. Which indicator during calibration most reliably suggests the meter and electrode are performing acceptably?
- Slope close to theoretical value, small offset, and passing control buffer check
- Very fast blinking screen only
- Random large differences between buffers without pattern
- Complete inability to stabilize in buffers
Correct Answer: Slope close to theoretical value, small offset, and passing control buffer check
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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