How a pipetting robot dilutes potency samples

A liquid handling robot is a gantry that carries a pipetting head over a deck of tip racks, sample tubes and plates. For a potency test, each plant extract is far too concentrated for the instrument, so the robot moves a small volume into fresh solvent, mixes, and repeats. Each step divides the concentration by the same factor, so a few steps bring the sample into the range the instrument was calibrated for.

Controls

Labels

Animation speed

Number of samples

Dilution factor per step

Dilution steps

Step through it

The deckEverything the robot touches sits at known positions on the deck: racks of clean tips, the sample extracts, a solvent reservoir, a strip of dilution tubes and a 96 well plate for the instrument.
The gantryMotors drive a beam front to back, a carriage side to side, and the pipetting head up and down. Those three straight moves reach any point on the deck.
Fresh tip every transferThe head presses onto a clean disposable tip, draws up liquid, dispenses it, then ejects the tip into the chute so no extract carries over into the next tube.
Serial dilutionEach tube in the strip holds solvent. The robot moves one part of the previous tube into it and mixes, so every tube is weaker than the one before by the same factor.
Gentle steps, many of themSet the factor to 2 and the steps to 6. Each step is mild, so the final sample is only 64 times weaker, while tips and run time keep growing.

The dilution math

If each step mixes one part of the previous solution into enough solvent to make F parts in total, the concentration falls by a factor of F every step. After n steps, the final concentration is C0 divided by F to the power n.

This model starts from an extract of 1,000 µg/mL, a round teaching value. Potency labs choose the factor and number of steps so the final sample lands inside the concentration range their chromatograph was calibrated to measure, then multiply the measured value back up by the total dilution.

Try it: keep 3 steps and slide the factor from 10 down to 2. The tubes in the strip stay darker and the final concentration jumps from 1 µg/mL to 125 µg/mL, while run time and tip count do not change at all.

Why robots, and why the time estimate is simplified

A robot repeats the same aspirate and dispense motions for hours without the drift and fatigue that hand pipetting brings, and it logs every transfer. This run time counts 8 moves per dilution step plus 2 per sample (tip on, aspirate, travel, dispense, mix, tip off, and a diluent fill) at about 4 seconds each. Real cycle times depend on volumes, mixing and the head; multichannel heads that work 8 or 96 wells at once cut the time dramatically.

Tips are counted as one fresh tip per transfer plus one for adding solvent to each sample's tubes. Labs track tip use closely because tips are a large share of consumable cost.

Sources

1.8: Serial Dilutions and Standard CurveLibreTexts Biology (ASCCC Open Educational Resources Initiative)
MathBench: Serial Dilution, the dilution factorUniversity of Maryland
Principles of computer-controlled linear motion applied to an open-source affordable liquid handler for automated micropipettingScientific Reports (open access)

How to cite this model

Avid Solutions International. (2026, November 11). How a pipetting robot dilutes potency samples [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/lab-liquid-handler

Last updated November 11, 2026

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