Improper pipetting technique is the single most common source of measurement error in analytical laboratories — occurring far more frequently than mechanical failure or calibration drift. The volume indicated on the counter display is meaningless if the technique used to aspirate and dispense it is flawed. Below is the correct operational sequence.
Before Pipetting
Select a micropipette matched to the target volume. Every micropipette has an optimal operating range (such as 2–20 µL, 20–200 µL, or 100–1000 µL). Setting a 20–200 µL micropipette to deliver 15 µL will yield significantly less accurate results than using a 2–20 µL instrument for the same volume — piston travel is too minimal to deliver calibrated precision at the extreme lower boundary of its range.
Attach compatible, properly fitting tips. An ill-fitting tip (wobbly or loose) compromises the airtight seal, causing aspirated volumes to deviate from the nominal setting. Mount the tip onto the nose cone with a gentle twisting motion until firmly seated; avoid repeatedly jamming or hammering straight down.
Equilibrate liquids and pipette to ambient room temperature. Pipetting cold liquids (retrieved directly from refrigeration) with a room-temperature micropipette causes the air cushion within the tip to expand upon warming, resulting in under-delivery of the target volume.
Forward Pipetting Technique
The standard method for aqueous solutions, buffers, and dilute reagents:
- Depress the operating plunger to the first stop (not the second stop).
- Immerse the tip 2–4 mm into the liquid — avoid deeper immersion, which allows excess liquid to adhere to the outer tip wall.
- Release the plunger smoothly and at a controlled pace, without snapping back. Wait approximately 1 second before withdrawing the tip, allowing the liquid column to reach full equilibrium.
- To dispense, place the tip aperture against the receiving vessel wall at a 10–45° angle. Depress the plunger to the first stop, pause briefly, then depress to the second stop (blow-out) to fully expel residual liquid.
- Withdraw the tip from the vessel wall before releasing the plunger — releasing while still touching the liquid or wall can re-aspirate delivered sample.
Pre-wetting the tip improves volumetric accuracy for small volumes: aspirate and dispense the liquid 2–3 times prior to actual measurement. This saturates the dead air space within the tip with vapor, preventing capillary evaporation that leads to under-delivery.
Reverse Pipetting Technique
For viscous liquids (such as glycerol or concentrated protein solutions) or liquids prone to foaming (buffers containing detergents or surfactants), forward pipetting often leaves residual liquid inside the tip or introduces air bubbles:
- Depress the operating plunger fully to the second stop (past the first stop).
- Immerse the tip into the liquid, then release the plunger smoothly to the rest position — this draws an excess volume beyond the calibrated setting.
- Deliver the target volume by depressing the plunger only to the first stop. The residual liquid remaining in the tip (the excess drawn in step 2) is discarded with the tip and not delivered into the receiving vessel.
Common Operational Errors
- Tilting the micropipette excessively during aspiration (greater than 20° from vertical) — alters hydrostatic head pressure, causing volume inconsistency.
- Inverting or laying down a micropipette containing aspirated liquid, allowing liquid to enter the shaft — corrodes internal seals, damages pistons, and necessitates professional servicing.
- Reusing tips across different samples — introduces cross-contamination risk, particularly in PCR assays and sterile cell culture workflows.
- Neglecting scheduled calibration. A micropipette in routine daily use should be calibrated every 6–12 months depending on workload intensity — internal seals and pistons experience mechanical wear regardless of user skill.
When Recalibration Is Required
Signs that an instrument requires inspection include inconsistent replicate delivery, increased resistance or roughness in plunger travel, or difficulty forming an airtight tip seal. IBS provides calibration and preventive maintenance services for micropipettes and analytical instruments across Indonesia — see our Support page for service scopes, or contact our technical team directly.
Browse our micropipette product line on the Laboratory Micropipettes page.
