Tips for pipetting volatile liquids (things like ethanol)
Pre-wet the tip (pipet up and down several times before the “real deal” to equilibrate the air).
Have you ever tried to pipet an ethanol solution & found that it just drips out of your pipet tip? This is because ethanol is volatile. This means it will evaporate easily. Especially if the pressure is low, making such escape as a gas easier. And one place where pressure is low is in the tip of a pipet (where low pressure helps suck up (aspirate) the desired volume of liquid). Therefore, when you pipet up liquid ethanol, some will evaporate into ethanol gas, and the added gas molecules will increase the pressure and expand, pushing the liquid out of the tip (even when you’re not pushing down on the plunger).
To prevent this, you can pipet up and down several times to saturate the air cushion with the maximum amount of volatile gas particles. This way, when you do your actual sample pipetting, there won’t be any change in pressure.
Try reverse pipetting.
Also helpful for pipetting viscous (goopy) solutions, reverse pipetting is where you suck up (aspirate) more liquid than you push out (dispense). Since some volume will remain in the tip after aspiration, if some had leaked out when you aspirated, it’s not an issue because the lost volume comes out of the extra (but it could be an issue if it dripped onto your sample, tubes, etc.!)
Try reverse pipetting, depress to the second stop when aspirating (sucking up liquid), then the first stop when dispensing (pushing the liquid out), leaving the leftovers in the tip (as opposed to the “normal” forward pipetting we typically do where you go down to first stop when aspirating (so you suck up just what you need) and the second stop when dispensing, pushing it all out.
More on this here: blog: https://bit.ly/pipetting_problems ; YouTube: https://youtu.be/AUTlgR4V6lI
If you want to get all fancy (and have the $) you can try a positive displacement pipet - these don’t use an air cushion, unlike your typical, negative displacement, pipet. Instead the plunger directly contacts the liquid. This way, there’s no air to expand so the volume won’t change.
Pipet very slowly.
These solutions have a tendency to jump up your pipet tip so pipet slowly, staying in control. Avoid sudden movements of your thumb, especially when doing the “blowout” step (pushing the final stuff out of the tip) - keep your thumb depressed while pulling out of the liquid. If some jumps up, don’t panic - instead, pipet slowly back up until liquid is in contact with the drops inside the tip, and let the liquid help pull the drop out.
Use solvent-resistant markers (or at least avoid dripping on your markings) and mark in multiple places just in case one washes off
blog form: https://bit.ly/pipettingvolatiles
More resources:
“How to Stop Dripping When Pipetting Volatile Liquids”, Eppendorf, 2019: https://handling-solutions.eppendorf.com/liquid-handling/pipetting-facts/pipetting-of-challenging-liquids/detailview/news/how-to-stop-dripping-when-pipetting-volatile-liquids/
Sartorius Techniques for Pipetting Challenging Liquids, Sandra Söderholm and Paulus Artimo, 2021 https://www.sartorius.com/resource/blob/1085646/d4bf11ef41cbbc9c7ebdcc88ecea4846/how-to-pipette-challenging-liquids-application-guide-en-l-sa-1--data.pdf
more practical lab tips & tricks: https://bit.ly/lab_tricks_page & https://www.youtube.com/playlist?list=PLUWsCDtjESrFEAWZCRKJL7sMc6a_KgfLU
more about all sorts of things: #365DaysOfScience All (with topics listed) 👉 http://bit.ly/2OllAB0 or search blog: http://thebumblingbiochemist.com