Volatility describes how easily a liquid can evaporate (turn into a gas or vapour) at ambient temperature and should be considered when designing your protocol in OneLab as it impacts the ability of the pipetting robot to properly transfer the liquid. This entails adjusting the pipetting parameters in OneLab by implementing commands specifically tailored for handling volatile solutions, thereby achieving improved pipetting performance and accurate transfer.

💨 Volatile Solutions: methanol, ethanol, isopropanol, acetone, formaldehyde, acetonitrile.

Pipetting Recommendations (see full article here)

The table below summarizes the general recommendations for optimal manual pipetting of volatile solutions.

Parameter

Recommendations for Best Pipetting Volatile Solutions 💨

Pipetting mode

Forward mode with air cushion control; Reverse pipetting is an alternative

Pipetting speed

Fast to minimize the effects of evaporation

Tip pre-wetting

Highly recommended to reduce dripping

Air cushion

Bottom air cushion if forward pipetting is used

Dispense tip position

On the fly, at the liquid level, or at the bottom

Pause before blow-out

Recommended

Pause after aspiration/dispensing

Not required

Touch off after dispensing

Not required

Rinse after dispensing

Not possible

Repetitive dispensing

Not suitable

Tip type

Standard

Tip filter

Recommended to eliminate exposure to harmful vapours and protect pipette integrity

OneLab Pipetting Settings

The table below provides instructions on how to set up the OneLab software, following either the "IDEAL Setup" scheme or the "ALTERNATIVE Setup" approach, to ensure optimal pipetting results when handling volatile solutions while getting the best out of the pipetting system, whether you are using the guided Pipette+ system or the Andrew+ pipetting robot.

Parameter

IDEAL Setup

ALTERNATIVE Setup

Pipetting mode

Forward

Reverse

Blow-out

Yes

Disabled

Pause before blow-out

Yes

Disabled

Aspiration speed

Fast

Fast (1)

Dispensing speed

Fast

Normal to fast

Air cushion

Air bottom cushion

Disabled

Pipetting moving speed

Slow

Slow (2)

Tip position at destination

w.r.t the liquid or the bottom; On-the-fly dispensing is feasible

w.r.t the liquid or the bottom; On-the-fly dispensing is feasible

Tip choice

Use tips w/ filter

Yes, if available

Yes, if available

Mixing at source ≡ Tip pre-wetting

Yes, two to three times at a fast speed

Yes (3), two to three times at a fast speed

Mixing at destination ≡ Rinse after dispensing

No

No

Custom tip position at the destination, customized dispensing height Liquid surface touch-off after dispensing

None

None

(1) Fast aspiration/dispensing speed = High flow rate

Helps minimize evaporation and therefore pressure inside the tip column which causes the liquid to drip out of the tip.

(2) Slow down the pipette movement during transit

Prevents liquid from dripping, thereby keeping the working area clean and contamination-free.

(3) Liquids with high vapour pressure are more likely to drip. Tip pre-wetting prior to aspiration is crucial to:

  • Saturate the air inside the pipette tip with vapours

  • Stabilize the pressure above the liquid column

  • Reduce liquid dripping during the transit

Pipetting Performance Evaluation

As a volatile solution, we used 50% Ethanol. The images above compare the pipetting output before and after dispensing 50% ethanol into a test tube containing distilled water, using either the IDEAL (Forward mode with air bottom cushion) or the ALTERNATIVE (Reverse mode) setup versus a default forward pipetting (without advanced control).

Based on the observations made during the test, the forward mode delivered the most accurate transfer with no dripping thanks to the combined action of tip pre-wetting and the air bottom cushion introduced after aspiration to hold the liquid in the tip during transit. The remaining liquid adhering to the tip end in (A) can be removed by ensuring that the dispense is properly performed with respect to the liquid surface or into the liquid followed by an adequate pause before the blow-out.

On the other hand, the reverse pipetting showed a good transfer with no to minimal dripping thanks to the tip pre-wetting. The system incorporates a larger sample volume to minimize the effect of evaporation on the actual liquid volume to be delivered. It could happen that this excess volume draws out of the tip during dispensing due to prolonged contact with the liquid inside the destination vessel since volatile liquids have low surface tension. To avoid this from happening during manual pipetting, one can decrease the time the tip stays in contact with the liquid. This action is also useful to reduce the time for droplet formation.

Using one or the other of the two previous modes, one should always make sure that the pipette tip is correctly immersed in the liquid both at the source and destination, (generally, a few millimetres below the liquid's surface depending on the size of the tip) to allow proper pipetting of the desired volume and therefore improve accuracy. Immersing the tip too deeply in the liquid can increase the risk of liquid droplets clinging to the outside of the tip or liquid carryover, resulting in inaccurate pipetting. The tip immersion depth at the source and/or the destination vessel can be adjusted in OneLab through the "custom tip position" parameter.

In contrast, when using default forward pipetting settings with no custom control, the liquid dripping increased and some residual liquid was observed in the tip after the blow-out without pause.

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