There’s long been a lively online debate about the merits of reusing pipette tips, versus sending them to landfills. This is despite the fact that for at least two decades ISO 8655-2 (governing “Piston-operated volumetric apparatus—Piston pipettes”) has stipulated:

“Pipette tips made of plastic for piston pipettes with air interface are designed for single use. They shall not be cleaned for reuse.”

Pipette tip reuse came to the fore during the pandemic. At that time supply chain issues left many labs without tips, while COVID PCR tests (a public health linchpin) were requiring several tips per test.

The pipette supply chain seems to be fine now, and home COVID tests are in ample supply. But it’s not irrational to ask if there is an alternative to single-use pipette tips. In 2021, the University of California, Santa Barbara (UCSB) noted that pipette tips and boxes were among the leading contributors to laboratory waste. According to UCSB, pipette tip boxes alone accounted for 80 percent of the plastic lab waste at MIT. It was around this time that we first dove into the topic, with a brief blog on quickly racking tips for sterilization and reuse.

Q: Is it OK to Reuse Pipette Tips? A: It’s Complicated!

Most discussions of pipette tip reuse focus on the possibility of cross-contamination—which is a valid concern. But a quick dip into ISO 8655-2 reveals that the real issue is more fundamental:

Micro-pipetting is all about precision and accuracy, and most plastic tips will not remain reliably accurate with multiple uses.  According to the original (2002) ISO 8655-2, reuse of pipette tips can lead to up to 4.0 percent error, far exceeding maximum permissible error for this equipment.

That said, ISO 8655-2 has always differentiated between air-displacement and positive-displacement pipette tips. This is, in fact, the source of some controversy.

Air-displacement pipettes are the ones most familiar to most lab workers. In this apparatus, there’s an air buffer between the piston and the liquid being pipetted. As such, the disposable plastic pipette tip is the only part of the device that comes into contact with the sample. This minimizes avenues for contamination. But it also makes precision and accuracy more challenging, especially with viscous or dense fluids, or under some ambient temperature and atmospheric conditions. Air-displacement pipettes work best with aqueous and non-viscous liquids.

Positive-displacement pipettes are somewhat less common, and designed very differently. Here the tip is a multi-part affair, with a sliding “capillary” (plunger) that goes all the way down the tip and can directly contact the fluid. This lends itself to repeatable precision, even with “problem liquids” (e.g., those that are dense, viscous, volatile, hot, cold, or foaming). But this design also increases costs and adds avenues of cross-contamination.

According to ISO 8655-2, positive-displacement pipette tips may be disposable or reusable. But the simpler plastic air-displacement pipette tips are not reusable.

Should Our Lab Be Reusing Pipette Tips?

In most labs, air-displacement pipettes with disposable tips are likely the norm. The combination of reduced risk of contamination, convenience, and lower cost is just too attractive. That being the case, ISO 8655-2 is unambiguous: You should use each tip once and then dispose of it.

However, many labs are making their own determination, based on the sensitivity of their work to contamination. Labs must also take into account the metrological issues that come with reusing disposable plastic air-displacement pipette tips between samples, let alone after autoclaving.

Uncomfortable with the mountain of plastic waste, yet unable to consider reusing plastic tips or shifting to positive-displacement pipettes with reusable tips?  Eppendorf’s bio-based pipette tips might be worth a look.