Liquid Handling for Viscous and Volatile Liquids: Tips and Tricks

Reverse Pipetting: A Technique for Difficult Liquids

Reverse pipetting intentionally aspirates more liquid than the target dispensing volume.

Instead of pressing the plunger only to the first stop before aspiration, you depress it to the second stop. After aspirating, dispense only to the first stop. The excess liquid remains in the tip and is discarded with the tip.

This technique can improve handling of:

• Glycerol-containing solutions
• Serum
• Concentrated glucose solutions
• Protein solutions
• Detergent-containing or foaming liquids
• Some volatile liquids

Reverse pipetting helps compensate for liquid retained inside the tip and reduces bubble formation during dispensing.

The tradeoff is higher reagent consumption. Because excess sample remains in the tip, reverse pipetting is not always appropriate for extremely limited or precious samples. In those cases, use a low-retention tip or positive displacement system and validate the method for the application.

Tip Selection for Difficult Liquids

Low-Retention Tips

Low-retention tips reduce wetting of the internal tip surface, helping more liquid leave the tip during dispensing.

They are particularly useful when pipetting viscous liquids, including:

• Glycerol solutions
• Serum
• Concentrated protein solutions
• Detergents and surfactants

Low-retention versions of Universal Pipette Tips or LTS-Compatible Pipette Tips can reduce residual volume without changing the basic pipetting workflow.

Positive Displacement Tips

For extremely viscous or volatile liquids, positive displacement pipettes provide greater control because a disposable piston directly contacts the liquid.

Eliminating the air cushion reduces errors caused by viscosity, vapor pressure, and temperature differences.

Filter Tips

Filter tips protect the pipette from aerosols and accidental liquid ingress, but a filter does not stop solvent vapor from affecting an air-displacement system.

Choose filter tips when contamination control is required—not as the primary solution for evaporation.

Extended-Length Tips

Extended tips can help access deep tubes or vessels while reducing the chance that the pipette shaft contacts the vessel rim.

Practical Techniques for Viscous Liquids

When handling glycerol, serum, concentrated protein solutions, or similar materials:

• Use reverse pipetting when sufficient sample volume is available.
• Aspirate slowly and smoothly.
• Pre-wet the tip 2–3 times with the working liquid.
• Keep the pipette close to vertical during aspiration.
• Allow 1–2 seconds after aspiration for the liquid to finish entering the tip.
• During dispensing, touch the tip gently against the vessel wall when appropriate.
• Pause briefly after dispensing to allow viscous liquid to drain.
• Use low-retention tips when residual liquid is visible or materially affects recovery.

For frequently repeated quantitative work, consider verifying or adjusting the pipetting method specifically for the liquid rather than assuming water-based calibration behavior will transfer directly.

Practical Techniques for Volatile Liquids

Volatile liquid pipetting is challenging because evaporation into the pipette's air cushion changes internal pressure.

For ethanol, isopropanol, and similar volatile liquids:

• Pre-wet the tip several times to condition the air space.
• Work efficiently and minimize unnecessary pauses.
• Keep aspiration and dispensing timing consistent.
• Consider reverse pipetting when the method has been validated.
• Use positive displacement for highly volatile solvents or when accuracy requirements are demanding.
• Avoid repeatedly aspirating volatile solvent with the same tip when evaporation or concentration changes could influence results.

Filter tips are not automatically required for volatile liquids. Use them when aerosol or contamination protection is needed and confirm material compatibility with the solvent.

Practical Techniques for Foaming Liquids

Detergents and many protein-containing solutions can generate bubbles when handled aggressively.

To reduce foaming:

• Aspirate slowly.
• Use reverse pipetting.
• Avoid vigorous mixing or repeated blow-out steps.
• Dispense gently against the vessel wall when appropriate.
• Use low-retention tips to reduce surface wetting and residual liquid.

Do not let the plunger snap back during aspiration. Rapid movement increases turbulence and bubble formation.

Comparison Table

When to Consider Positive Displacement Pipetting

Move beyond conventional air displacement when changing technique and tip type still do not provide acceptable accuracy or precision.

Positive displacement is particularly appropriate for:

• Highly viscous samples
• Highly volatile solvents
• Dense liquids
• Samples with high vapor pressure
• Very small transfers of difficult liquids

Because the piston contacts the liquid directly, positive displacement minimizes the influence of the compressible air cushion.

For automated workflows involving difficult liquids, use compatible Automation Tips and optimize the liquid class—including aspiration speed, dispense speed, tip position, and delays—rather than relying on the tip alone.

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