Tips get bought by the case and grabbed by the box, so it is easy to forget they are not all interchangeable. The tip is where the liquid actually sits during a transfer, and its bore, length, and surface chemistry all change how that liquid moves. A class validated on one tip can quietly miss on another, which makes the tip as much a part of the class as any flow rate in it.
Match the volume range first
A tip has a working range, and accuracy falls off at the edges of it. Dispensing 2 microliters from a 1000 microliter tip asks the instrument to resolve a sliver of the tip volume, where small errors become large percentages. Pick a tip whose range brackets your target volume with room to spare, and if your protocol spans a wide range, expect to use more than one tip and more than one class rather than forcing a single tip to do everything.
Coatings and geometry change the liquid
- Filtered tips put a barrier between liquid and instrument, guarding against aerosols and cross-contamination for sensitive work such as PCR setup.
- Conductive tips are what capacitive level detection needs to sense the surface, so a class that relies on that detection assumes them.
- Wide-bore tips lower the pressure needed to move thick liquids or to handle cells and beads gently, which is why viscous and cell-based classes often call for them.
- Low-retention tips carry a surface coating that sheds the last film of liquid, cutting the volume left behind with surfactant-laden or precious reagents.
Fixed tips are a different world
Everything above assumes disposable tips. Fixed steel tips, washed and reused, behave differently again: they wet differently, carry over unless washed well, and pair with a system-liquid fluidic path rather than an air cushion. A class built for disposable tips does not simply drop onto fixed tips, and the reverse is equally true.
Change the tip, re-check the class
The practical rule follows from all of this: if the tip changes, the class is no longer validated until you re-check it. A different geometry, coating, or even a different lot can shift retention and wetting enough to move your volumes. It is usually a quick gravimetric re-check rather than a full redevelopment, but it is not optional.