Top 50 Pharma QC Interview Questions and Answers

In short: These are 50 Quality Control (QC) interview questions with model answers, grouped by topic: GMP and documentation, HPLC and GC, other instruments, qualification, OOS and OOT, stability, reference standards, method validation, lab safety and behavioural questions. Answers are short and practical so you can say them aloud. Where a limit comes from a pharmacopoeia or your product specification, the answer tells you to name the source rather than quote a number from memory.

This is a deeper, QC-only companion to our general QA/QC interview questions page, which covers QA systems, process validation and cleaning validation. The questions below do not repeat that page. If you are applying right now, also look at the current fresher jobs and practise with the QC interview question set.

How to prepare in one evening

• Pick the instruments on your CV. Interviewers go deep on what you wrote. If you list HPLC, be ready for system suitability, column care and a troubleshooting story.
• Learn the logic, not numbers. Acceptance limits for system suitability, dissolution or disintegration come from the current pharmacopoeia chapter or the approved method. Saying “I would check the monograph and the approved method” is a correct answer; a wrong remembered number is not.
• Prepare two real examples. One time you found a mistake in data, and one time you followed a procedure when it was inconvenient.
• Answer in three parts. What it is, why it matters, what record proves it.

Section 1: GMP, documentation and data integrity

1. What does GMP mean for a QC laboratory?

GMP in QC means that testing is done by trained people, with calibrated instruments, approved methods and qualified standards, and that every step is recorded so another person can reconstruct it. The laboratory results are the evidence on which a batch is released, so the lab is held to the same standard as production. In the US, the lab-specific rules are in 21 CFR Part 211 Subpart I (laboratory controls).

2. What is ALCOA+?

It is a set of data-quality attributes: Attributable, Legible, Contemporaneous, Original and Accurate, with the “plus” covering Complete, Consistent, Enduring and Available. In the lab it means you write or record at the time of the work, sign and date your own entries, and keep the original data. Our article on data integrity in FDA warning letters shows how failures against these points appear in inspections.

3. What must a laboratory record contain?

Under 21 CFR 211.194(a) it must include complete data from all tests needed to show compliance with specifications: sample description, the method used, the weight or measure of sample, all graphs, charts and spectra, all calculations, the results compared with standards, the analyst’s initials or signature and date, and a second person’s review for accuracy and completeness. In an interview, list these in order of the testing day and you will cover most of it.

4. What is the difference between good documentation practice and data integrity?

Good documentation practice is how you write: indelible ink, single-line cross-outs with reason, date and signature, no overwriting. Data integrity is the wider assurance that data stay complete, consistent and accurate across their whole life, including electronic data, audit trails and backups. GDP is one of the tools that delivers data integrity.

5. How do you correct a mistake in a paper logbook?

Draw a single line through the entry so it stays readable, write the correct value next to it, add your initials, the date and a short reason where the procedure requires it. Never use correction fluid, never tear out pages and never write over the original. If the mistake affects a result, tell your supervisor before continuing.

6. What is an audit trail and who reviews it?

An audit trail is the secure, time-stamped record of who created, changed or deleted electronic data, and why. The chromatography data system should have it switched on and unalterable by analysts. Review of the audit trail for the relevant runs is part of data review, typically done by the reviewer or QA under the site procedure, before results are approved.

7. Why should an analyst not trial-inject or “pre-run” samples without recording it?

Because unrecorded testing hides data. If a sample is run to see whether it passes and the result is not documented, that is testing into compliance, and it is one of the most cited data-integrity failures. Any injection of a sample or standard for a real batch is either part of the record or an investigated event.

8. How long should QC records be kept?

Laboratory records belong with the batch documentation, which is kept at least 1 year after the expiry date of the respective product batch (EU GMP Part I Chapter 4 §4.11 and 21 CFR 211.180(a)), longer if local law or the marketing authorisation requires. Your site SOP states the exact rule, so quote it and mention it can be longer.

9. What is a controlled document, and why must an analyst use only the current version?

A controlled document is issued with a number, version and effective date, and only the current approved version is in use at the point of work. Testing with an obsolete method or specification means the result is not valid for batch release. Uncontrolled photocopies or personal printouts are a common audit finding.

10. What is sample traceability in the lab?

Every sample must be traceable from receipt to disposal: unique identification, source, quantity, date received, storage condition, the analyst who tested it and what remains. Retention samples and leftover test solutions are handled according to the SOP, and nothing is discarded before the result is approved.

Section 2: HPLC and GC

11. What is system suitability and why is it done?

System suitability is a check, run on the day with the actual column, mobile phase and instrument, that the whole system is working well enough for the method to give reliable results. The criteria are written in the monograph or validated method; typical parameters are repeatability of standard injections, resolution, tailing and sometimes plate count. If it fails, the sample results from that run are not reported and the cause is investigated.

12. Which system suitability parameters do you know?

Repeatability (percentage RSD of replicate standard injections), resolution between critical peaks, tailing factor (called symmetry factor in Ph. Eur.), theoretical plates and, for impurity methods, signal-to-noise at the reporting level. The exact limits come from the current pharmacopoeial general chapter on chromatography, or the validated method.

13. What is resolution and what do you do if it drops?

Resolution describes how well two adjacent peaks are separated, using their retention-time difference and peak widths. If it drops, check the mobile phase preparation and pH, the column age and temperature, flow rate, and whether extra-column volume (a wrong tubing or a loose fitting) has been introduced. Fix one factor at a time and record each change. Our HPLC troubleshooting steps article gives a fuller checklist.

14. What causes peak tailing?

Common causes are a worn or contaminated column, secondary interactions of basic compounds with silanol groups, a mobile phase pH unsuited to the analyte, a blocked frit, sample solvent stronger than the mobile phase, or a void at the column head. Tailing is first assessed against the tailing factor in the method, then diagnosed from the cause that fits the pattern.

15. What is the RSD and why is it checked on replicate injections?

Relative standard deviation is the standard deviation expressed as a percentage of the mean. On replicate standard injections it shows how repeatable the injector, pump and detector are working together. A high RSD points to air in the system, a leaking seal, an unstable baseline or an injector problem, not to the sample.

16. What do retention time shifts tell you?

A gradual drift in one direction often means mobile phase composition is changing (evaporation of the organic component) or the column is not equilibrated. A sudden shift suggests a flow problem, leak, wrong mobile phase or temperature change. Compare with the standard injected in the same run to see whether the shift affects every peak.

17. How do you take care of an HPLC column?

Use only the filtered, degassed solvents named in the method, flush buffers out with water and then store in the recommended solvent, never let a buffered column dry out or sit in salt, use a guard column when the sample matrix is dirty, and stay inside the column’s pH and pressure range. Keep a column logbook with the column ID, number of injections, method and storage so you can see performance trends.

18. What is a blank, a placebo and a standard injection used for?

A blank (diluent) shows whether the system or solvent gives interfering peaks. A placebo shows whether excipients interfere with the analyte peak. A standard gives the reference response for calculation and for system suitability. All three can be needed in one sequence, in the order the method states.

19. Why do we filter and degas the mobile phase?

Particles block frits and damage the column and pump seals; dissolved gas forms bubbles that cause baseline noise, pressure fluctuations and flow errors. Use the filter membrane the method allows, and remember that some filters can adsorb the analyte, so filter compatibility is checked during method development.

20. What is the difference between isocratic and gradient elution?

Isocratic uses a constant mobile phase composition throughout the run. Gradient changes the composition over time to separate compounds with a wide range of polarities in a reasonable run time. Gradient methods need good equilibration between injections and a blank gradient run to check for ghost peaks.

21. How is GC different from HPLC in the QC lab?

GC separates volatile or thermally stable compounds in a gas stream through a column in an oven; HPLC uses a liquid mobile phase for non-volatile or heat-sensitive compounds. In QC, GC is common for residual solvents. Typical issues are septum bleed, liner contamination and carrier-gas leaks, covered in our GC troubleshooting guide.

22. How is HPLC performance checked beyond system suitability?

Periodic calibration and performance qualification of the pump flow, injector, column oven, detector and sampling accuracy, done at the frequency and with the acceptance limits in the approved SOP. System suitability does not replace this scheduled work; read our HPLC calibration guide for the usual modules.

Section 3: UV, IR, KF, pH, dissolution and disintegration

23. How do you verify a UV-Visible spectrophotometer before use?

Typically by checking wavelength accuracy, absorbance accuracy, stray light and resolution at the frequency in your calibration SOP, and by running a baseline or blank on the day. The reference materials and limits come from the pharmacopoeia or the manufacturer’s procedure. See our UV-Visible spectrophotometer SOP for an example in-house format.

24. What is Beer-Lambert law and where does it fail?

Absorbance is proportional to the concentration of the absorbing species and the path length. It fails at high concentrations, with stray light, when the analyte associates or reacts in solution, or when the solvent absorbs at the working wavelength. This is why test solutions are prepared to fall within the validated linear range.

25. What cuvette precautions do you follow?

Use matched cuvettes of the right material (quartz for UV, since glass absorbs there), hold them by the frosted sides, rinse with the solution, wipe the optical faces with lint-free tissue and make sure no bubbles are in the light path. Always use the same orientation and run the blank in the same cuvette.

26. What does FTIR identification rely on?

The infrared spectrum of a substance is a characteristic fingerprint. Identification compares the sample spectrum with that of the reference standard or the reference spectrum of the monograph, with the same preparation technique (for example ATR or KBr). Check the instrument with the pharmacopoeial verification before the sample.

27. Explain the principle of Karl Fischer titration.

Karl Fischer titration measures water by a reaction in which iodine consumes water in the presence of sulphur dioxide, a base and an alcohol. In volumetric KF the titre of the reagent is standardised with a water standard before use, and the titration endpoint is detected electrochemically. In coulometric KF iodine is generated electrochemically, which suits very low water content.

28. Why is KF titrant standardised, and how often?

The titre (mg of water per mL) falls over time as the reagent picks up moisture. It is standardised against a water standard or sodium tartrate dihydrate before use and at the frequency of the approved method.

29. What is the difference between LOD and water content by KF?

Loss on drying measures all volatile matter lost under the stated conditions, which can include solvents, not only water. KF is specific to water. If both are reported for one material, they can differ, and the specification names which test applies.

30. How do you calibrate a pH meter?

Use fresh certified buffer solutions that bracket the expected sample pH, rinse the electrode between buffers, allow readings to stabilise at the stated temperature, and check the slope or response against the SOP limits. Record buffer lots and expiry. See our pH meter SOP for an example format.

31. What are the common sources of error in pH measurement?

A dry or aged electrode, blocked junction, expired buffers, a temperature difference between buffer and sample, carry-over between samples and low-ionic-strength samples that respond slowly. Store the electrode in the solution the manufacturer recommends, not in distilled water.

32. Why do we perform dissolution testing?

Dissolution shows how fast and how much of the active ingredient is released from a solid dosage form into a medium under defined conditions, which is linked to product performance and batch consistency. The apparatus, medium, speed, time and acceptance criteria come from the monograph or the approved specification, and the staged acceptance rule comes from the pharmacopoeial chapter.

33. What prevents a dissolution result from being reliable?

Dissolved gas in the medium, wrong medium volume or temperature, vibration, a mis-centred or tilted shaft or basket, sinkers used inconsistently, delayed sampling, filter adsorption and sample-solution instability. Mechanical qualification and performance verification of the apparatus are done on the schedule in the SOP; see our dissolution apparatus SOP.

34. What does a disintegration test show, and how is it different from dissolution?

Disintegration shows that the dosage form breaks into particles or fragments within the stated time in the specified fluid and apparatus. It does not show that the drug has dissolved. A tablet can disintegrate and still dissolve slowly, which is why dissolution is the more informative test. Apparatus checks are in our disintegration tester SOP.

Section 4: Calibration, qualification and reference standards

35. What is the difference between calibration and qualification?

Calibration compares an instrument’s readings with a traceable standard and records any error against defined limits. Qualification is the documented evidence that equipment is installed correctly and works as intended for its use. Calibration is part of keeping a qualified instrument in a state of control. Our calibration SOP gives an example in-house format.

36. Explain DQ, IQ, OQ and PQ for a new HPLC.

Design qualification confirms that the specification meets the intended use. Installation qualification checks the instrument as delivered and installed: model, serial numbers, utilities, software versions. Operational qualification tests the functions across their operating ranges, such as flow accuracy, temperature and detector linearity. Performance qualification shows that it performs consistently with the actual method under routine conditions. See qualification stages for the flow.

37. What happens if an instrument is found out of calibration?

Stop using it, label it, and tell QA. Then assess the impact: review the results generated since the last successful calibration on that instrument and decide, under the deviation procedure, whether any reported result is affected. 21 CFR 211.160(b)(4) requires calibration at suitable intervals to written programs with limits, and 211.194(d) requires the calibration records.

38. What is the difference between a primary and a working standard?

A primary (or compendial) standard is obtained from a pharmacopoeia or recognised authority and its assigned value is accepted without further comparison. A working (secondary) standard is prepared in-house, qualified against the primary standard, and used for routine testing. Read our article on reference substances and reference materials.

39. How do you qualify an in-house working standard?

Obtain a well-characterised batch, test identity, purity (assay, related substances, water or LOD, residual solvents as relevant) and compare it against the primary standard by the approved protocol, then assign a potency and a re-test date, with a CoA that records the data. 21 CFR 211.194(c) requires complete records of testing and standardisation of reference standards, reagents and standard solutions.

40. How do you handle and store reference standards?

Store them in the labelled condition (for example in a desiccator or refrigerator), record opening date and use, equilibrate to room temperature before opening cold containers, weigh quickly, and never return unused material to the container. Use the potency as stated on the current certificate, correcting for water or purity where the label requires.

Section 5: OOS, OOT and investigations

41. What is an OOS result and what do you do first?

A result outside the specification limit. Do not retest or discard; tell your supervisor, preserve everything (solutions, glassware, chromatograms) and start the laboratory investigation for obvious assignable causes such as calculation or dilution errors, under the OOS SOP. Our OOS investigation guide walks through both phases.

42. What is the difference between OOS and OOT?

OOS is a result beyond a specification limit. OOT is a result still within the specification but out of line with the earlier trend, for example a stability assay falling faster than prior batches. OOT calls for a documented evaluation under the site procedure; the way OOT is detected and the criteria are set by the site.

43. Can you retest after an OOS result?

Only as the SOP and an investigation allow, with the number and scope of any retest defined beforehand, and not as a way of testing until a passing number appears. All results, including the original, stay in the record. The decision on the batch rests on the full investigation, not on a single “good” retest.

Section 6: Stability and method validation

44. What are the ICH Q1A(R2) storage conditions for long-term, intermediate and accelerated studies?

For the general case in drug products: long-term at 25 °C ± 2 °C / 60% RH ± 5% RH or 30 °C ± 2 °C / 65% RH ± 5% RH, intermediate at 30 °C ± 2 °C / 65% RH ± 5% RH, and accelerated at 40 °C ± 2 °C / 75% RH ± 5% RH for six months. Long-term data cover at least 12 months at submission. Mention that Q1A(R2) addresses climatic zones I and II, so hot and humid markets also need the applicable regional guidance.

45. What are climatic zones and why do they matter?

The world is divided into four climatic zones (I to IV) by long-term temperature and humidity, and the storage condition used in the stability study should reflect where the product will be marketed. Q1A(R2) states that it addresses zones I and II; for zones III and IV, check the relevant regional or WHO guidance. WHO TRS 1010, Annex 10 (2018) gives these long-term conditions: zone II 25 °C / 60% RH, zone IVa 30 °C / 65% RH and zone IVb 30 °C / 75% RH (each ± 2 °C / ± 5% RH).

46. What do you do when a stability sample is not pulled on schedule?

Record the deviation, note the actual pull date and storage, tell QA, and evaluate whether the result can still be reported against the protocol time point. The protocol and SOP define the permitted window, so do not state a number from memory.

47. Which parameters does ICH Q2(R2) cover in method validation?

The characteristics to validate depend on the type of procedure (ICH Q2(R2) Table 1):

• Identification: specificity.
• Impurity, quantitative: specificity, response, quantitation limit, accuracy, repeatability and intermediate precision.
• Impurity, limit test: specificity and detection limit.
• Assay: specificity, response, accuracy, repeatability and intermediate precision.

Reproducibility is usually not required for a regulatory submission (§3.3.2.3). Robustness is evaluated during development (see ICH Q14) rather than listed in Table 1.

48. What is the difference between validation, verification and transfer?

Validation shows a new or non-compendial method is fit for its intended use. Verification shows that a compendial method works under actual conditions of use in your laboratory, as 21 CFR 211.194(a)(2) requires. Transfer is the documented qualification of a receiving laboratory to run an already validated method.

Section 7: Lab safety and behavioural questions

49. What are the key safety rules in a QC lab?

Wear lab coat, safety glasses and the right gloves; work with volatile or toxic solvents in a fume hood; know where the eyewash, shower, fire extinguisher and spill kit are; read the safety data sheet before using a new chemical; never pipette by mouth; add acid to water, not water to acid; and segregate and label solvent and chemical waste. Report every spill or injury to your supervisor at once.

50. Tell me about a time you found a mistake in your own work. (Behavioural)

A good model answer: “While reviewing my calculation after a content test I saw that I had used the wrong dilution factor. I told my supervisor the same day, did not change the original entry but corrected it per GDP with a reason, and we checked whether the result changed. I now cross-check dilution factors against the worksheet before signing.” This shows honesty, procedure and learning, which is what the interviewer wants.

Other behavioural prompts to prepare: “What would you do if your senior asks you to skip a calibration check because the batch is urgent?” (Answer: explain the risk politely, offer the quickest compliant option, and escalate to QA if pressed.) And “How do you manage pending samples when several are urgent?” (Answer: prioritise by hold time, release deadline and stability pull dates, and communicate early.)

Frequently asked questions

Do freshers need to know OOS and data integrity?

Yes. Even entry-level QC roles are expected to know that results are never altered or hidden, and what to do on an unexpected result. Questions 2, 5 and 41 cover the basics.

Should I quote numeric limits in an interview?

Quote only those you are sure about, such as the Q1A(R2) conditions, and say that product-specific limits come from the monograph or approved specification.

What is the best way to practise?

Say each answer aloud in under a minute, then check it against the approved SOP or guideline. Pair this page with our OOS guide and the QC question set.

References

• US Electronic Code of Federal Regulations, 21 CFR §§211.160(b), 211.180(a) and 211.194, Part 211, read as current on 28 October 2026.
• European Commission, EudraLex Volume 4, Part I, Chapter 4, Documentation, §4.11 (retention). EudraLex index.
• International Council for Harmonisation (ICH), Q1A(R2), Stability Testing of New Drug Substances and Products, Step 4, 6 February 2003. Official guideline.
• ICH, Q2(R2), Validation of Analytical Procedures, (Step 4, 1 November 2023, with error corrections of 30 November 2023). Official guideline.
• World Health Organization, WHO Technical Report Series No. 1010, 2018, Annex 10: Guidelines on stability testing of active pharmaceutical ingredients and finished pharmaceutical products. PDF on who.int.