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Laboratory technician interview questions and how to answer them

Lab interviews test one thing above everything else: can the lab trust your numbers. Expect questions about what you do when a result looks wrong, how you document, and how carefully you handle chemicals. Expect at least one practical check of your math or technique too. The questions shift with the lab: a pharma QC lab leans on documentation and investigations, an environmental lab on chain of custody and holding times, and a research group on how fast you pick up new protocols. Read the posting for the samples and instruments it names, then prepare a real story for each one you've touched.

12 questions6 minute read

Part 1

1.A sample result comes back out of specification. Walk me through what you do.

Why they ask

This is the most important question in a regulated lab. They want to know you won't just retest until it passes.

How to answer

  • Stop and don't discard anything: keep the sample, the preps and the raw data
  • Check for obvious lab error first: standards, reagents, instrument checks, calculations
  • Tell the supervisor promptly and follow the lab's OOS procedure
  • Only retest when the procedure allows it, and document every step

2.How do you keep a lab notebook or LIMS entry that someone else could follow?

Why they ask

Records are the product in many labs. An audit can pull any entry long after you've forgotten the day.

How to answer

  • Record in real time, in ink or directly in the system, never on scrap paper
  • Include lot numbers, instrument IDs, expiry dates and any deviation
  • Correct errors with a single line, initials and a reason, never erasing
  • Mention good documentation practice or ALCOA if you know the term

3.Which instruments have you run on your own, and what did you do when one misbehaved?

Why they ask

Postings list instruments, and they want to separate hands-on use from having seen one demonstrated in a class.

How to answer

  • Name each instrument honestly and say what level you ran it at
  • Describe a real problem, such as drifting HPLC pressure or a balance failing its check
  • Say how you troubleshot it and when you escalated to the supervisor or vendor
  • Show that you took the instrument out of use until it was fixed
4.How would you make a working solution from a stock solution?

Why they ask

Dilution math errors cause plenty of bad results, and this is quick to check live.

How to answer

  • Use the concentration and volume relationship and show the setup out loud
  • Pick the right glassware: volumetric flasks and pipettes for accuracy
  • Label with contents, concentration, date made, preparer and expiry
  • Double check the units before you touch a reagent
5.Tell me about a time you noticed a mistake, yours or someone else's.

Why they ask

Labs need people who speak up. A hidden mistake is far worse than a reported one.

How to answer

  • Pick a real, specific example involving a sample or a record
  • Say how you raised it and to whom
  • Explain what changed afterwards so it didn't repeat

Part 2

6.How do you handle a chemical you haven't worked with before?

Why they ask

Safety culture shows up fast in this answer.

How to answer

  • Read the safety data sheet before opening it
  • Choose the right PPE and use the fume hood when it's called for
  • Know where the eyewash, safety shower and spill kit are
  • Store and dispose of it per the label and the lab's waste rules
7.Your supervisor needs a rush result, but the balance fails its daily check. What do you do?

Why they ask

They want to see whether pressure changes your standards.

How to answer

  • Don't use the balance, even for a quick weighing
  • Tag it out and tell the supervisor immediately
  • Offer a fix: a backup balance that passed its check, or a revised time
  • Log the failure so it gets serviced
8.What does chain of custody mean, and when does it matter?

Why they ask

Environmental, forensic and contract testing labs live by it, and many plants use similar sample tracking.

How to answer

  • It's the signed record of who held the sample from collection to disposal
  • It matters whenever results could be used in court or by a regulator
  • Describe checking seals, times and signatures when you receive samples
9.How do you organise a day with more samples than time?

Why they ask

Queues back up in every lab. They want to know you'll prioritise sensibly.

How to answer

  • Check which samples have holding times or release deadlines
  • Batch similar tests and start the long runs first
  • Tell the supervisor early if something won't make it
10.Why this lab, and why this kind of testing?

Why they ask

They want to know you understand the samples, whether that's food, pharma, water or research.

How to answer

  • Name what the lab actually tests and connect it to your coursework or past work
  • Say which part of the routine you'd enjoy
  • Be honest about what you'd need to learn

Part 3

11.How do you know an instrument run is valid before you report the samples?

Why they ask

Chromatography and spectroscopy labs rely on system suitability, blanks and check standards. This separates people who press start from people who read the data.

How to answer

  • Check system suitability criteria in the method: resolution, tailing, repeatability of standard injections
  • Look at blanks for carryover and at bracketing standards for drift
  • Confirm the calibration curve meets the method's acceptance limits
  • If anything fails, stop, don't report, and follow the lab's procedure
12.Tell me about sharing a bench with a coworker whose habits bothered you.

Why they ask

Shared benches, shared instruments and shift handoffs create friction.

How to answer

  • Describe the habit concretely, like leaving unlabeled tubes in the fridge
  • Show that you raised it directly and calmly first
  • Explain the result and what you learned about working in a shared space

Questions to ask them

Ask at least two. It shows you're picking them too.

  • What does a normal sample load look like, and how often does it spike?
  • How do you train new techs on methods before they report results on their own?
  • What happens here when a result is out of specification?
  • Which instruments would I run most, and who maintains them?
  • What does the path from technician to senior tech or chemist look like here?

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