ISAC Equipment Operation and Maintenance 2

Question 1

What is the purpose of the sheath fluid in a flow cytometer?

Accepted Answer

To hydrodynamically focus cells into a single-file stream

Answer

Sheath fluid creates laminar flow that hydrodynamically focuses the sample stream so cells pass through the laser interrogation point one at a time.

Question 2

Which parameter is used to measure cell granularity in flow cytometry?

Accepted Answer

Side scatter (SSC)

Answer

Side scatter (SSC) measures light scattered at roughly 90 degrees and correlates with internal complexity and granularity of cells.

Question 3

When performing daily QC on a flow cytometer, which action is most important to perform FIRST?

Accepted Answer

Warm up the laser for the manufacturer-specified time

Answer

Lasers require a warm-up period to reach stable power output before any QC beads or samples are run.

Question 4

A flow cytometer's CV (coefficient of variation) for a fluorescent bead population is suddenly much higher than usual. What is the MOST likely cause?

Accepted Answer

Partial clogging of the flow cell or sample injection tube

Answer

Partial clogging causes unstable sample flow rate, leading to increased variation in signal intensity and a higher CV.

Question 5

What does 'backflushing' the flow cytometer accomplish during maintenance?

Accepted Answer

It reverses the flow direction to clear clogs from the sample line

Answer

Backflushing reverses sheath or DI water flow through the sample injection tube to dislodge and clear partial blockages.

(ISAC) International Society for the Advancement of Cytometry Practice Test