Air gaps and blowout are two of the smallest numbers in a liquid class and two of the most commonly misconfigured. They do not change the target volume directly, which is why people leave them at defaults, but they decide whether that volume actually reaches the well or drips down the outside of the tip.
What an air gap does
An air gap is a deliberate pocket of air aspirated along with the liquid. A trailing air gap, drawn after the liquid, sits at the tip opening and holds the liquid column back so it does not drip during transport. A leading air gap, drawn before the liquid, gives the dispense a final push. Volatile solvents and low-viscosity liquids benefit most, because they are the ones that drip.
What blowout does
Blowout is an extra plunger movement at the end of a dispense that expels the last residual liquid from the tip. Without it, a small, variable amount stays behind, and that variability shows up as imprecision. With too much of it, you can splash or generate aerosols. The right blowout clears the tip cleanly without disturbing the delivered volume.
How they interact with carryover
Carryover is liquid from one transfer contaminating the next. Correct air gaps and blowout reduce it by ensuring the tip is fully cleared between dispenses, but they are not a substitute for tip changes when cross-contamination must be near zero. Treat them as the first line of defense, not the only one.
- Increase the trailing air gap if you see droplets forming at the tip during transport.
- Add or increase blowout if replicate volumes are accurate on average but noisy.
- Reduce blowout if you observe splashing or foaming on dispense.
- Change tips, not just parameters, when carryover must be eliminated rather than minimized.
Air gaps and blowout are cheap to change and easy to test. Adjust one at a time and confirm the effect gravimetrically before moving on.