How to use a pipette: Depth of aspiration

Best pipetting practices

Hi there, how you aspirate liquids could be messing with your results. Did you know, that a common mistake, made during aspiration, comes from the need to place the pipette tip as deep as possible in the source vessel? Nobody wants to aspirate air. However this can lead to problems. The deeper the tip is submerged in a source liquid, the more problems may occur.

You might have excess liquid sticking to the outside of the tip. We call this liquid carry over and this could eventually make its way to whatever you are dispensing and throw off the results. In addition the risk of cross-contamination is higher. Carryover is not the only problem associated with aspirating too deep from a source. Typically the deeper your tip is submerged during aspiration, the more liquid will enter your tip.

You might wind up with more liquid than you intended. It's recommended, to insert the tip only two to three millimeters into the source liquid for aspiration. By using the wall of your source vessel to help guide you, this can be easy to accomplish.

One exception to this is, when aspirating extremely low volumes or about 0.2 microliters. Here your best bet is to go fairly deep with aspiration to ensure liquid is actually entering your tip.

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