Tips to Improve Pipetting of Viscous solution
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The importance of understanding and developing an optimal pipetting technique grows as your laboratory’s demand for accuracy and precision does. We will walk you through the steps and tips that will help you bring your pipetting to the next level in your everyday pipetting practices.
- Pre-wet the pipette tip
To minimize sample loss due to evaporation within the tip during sample delivery, it is recommended to aspirate and expel any liquid sample at least three times before aspirating a sample for delivery. Pre-wetting the tip before aspirating a sample can help maintain the humidity within the tip and reduce any variation in sample evaporation, which can lead to more accurate and precise results.
It is important to note that using the same tip to deliver multiple samples without pre-wetting can result in lower volume in the initial few samples, which can affect the accuracy of the results. This issue becomes more significant when working with volatile samples, such as organic solvents, as they are more prone to evaporation.
- Work at temperature equilibrium
To ensure accurate and precise results, it is recommended to allow both liquids and equipment to equilibrate to ambient temperature before pipetting. This is because the volume of liquid delivered by air displacement pipettes is dependent on several factors, such as the relative humidity and vapor pressure of the liquid, both of which are influenced by temperature.
To minimize variation in pipetted volume, it is crucial to work at a constant temperature. Temperature differences can cause the air space in the pipette to expand or shrink, leading to inaccuracies in pipetted volume. Therefore, allowing the pipette and liquid to equilibrate to ambient temperature before pipetting can help minimize the issue.
After temperature equilibrium, the main influencing factor on pipetted volume is the liquid density. When pipetting cold liquid, the liquid is more dense, while hot liquid is less dense compared to room temperature liquids. This means that the volume of liquid delivered by a pipette can vary depending on the temperature of the liquid, which highlights the importance of working at a constant temperature.
- Examine the pipette tip for droplets
It is important to carefully remove any droplets present on the outside of the tip before dispensing to ensure accurate and precise pipetting results. This can be done by touching the side of the reservoir with the tip, making sure to avoid touching the tip opening, as this can cause liquid to wick out the tip. Removing droplets from the outside of the tip can help prevent inaccuracies in pipetting due to the presence of excess liquid.
After dispensing, it is important to deliver any residual liquid remaining in the tip by touching the tip to the side of the container. This can help remove any excess liquid from the tip and ensure that the intended volume of liquid is delivered. By using the surface tension of the liquid, any residual liquid can be drawn out of the tip.
- Select a forward or reverse pipette based on the liquid
To properly aspirate and dispense liquids using a pipette, it is important to follow certain guidelines. Start by depressing the plunger to the first stop, and then immerse the tip into the liquid. Aspirate by releasing the plunger, which will allow the liquid to be drawn up into the pipette. Once you have the desired volume, remove the pipette from the liquid and depress the plunger to the second stop to dispense the entire contents. When using a pipette, it is generally recommended to use the standard (or forward) mode of pipetting, as it yields better accuracy and precision for most liquids. Reverse mode, on the other hand, can often result in over-delivery, particularly for less viscous or volatile liquids. It is important to evaluate the effect of possible over-delivery in your experiment and make adjustments as needed to ensure accuracy and precision.
- Pause consistently after aspiration
It is essential to pay attention to the timing of your movements when aspirating and dispensing liquids with a pipette. After aspirating the sample, it is recommended to leave the tip still in the liquid for about one second. This allows the liquid in the tip to settle and ensures that the volume is not too low due to residual movement. It is important to make these pauses as consistent as possible, as variations in timing can lead to variability in results. By taking care to pursue for the same amount of time after each aspiration, you can minimize these sources of variability and ensure more accurate and precise pipetting results.
Original source: https://accumaximum.com/blogs/tips-to-improve-pipetting-of-viscous-solution/
