The precision and accuracy of even the best calibrated pipette can be wiped out if you choose the wrong kind of tips. Depending on the experiment you are doing, the wrong kind of tips can also make your pipette a source of contamination, lead to waste of precious samples or reagents—or even cause you physical harm in the form of repetitive stress injury (RSI).
There are so many different kinds of tips to choose from. How do you know which is the best for your pipette and situation? Never fear, that’s what we are here for. This short guide will help you understand your options so that you can choose the correct pipette tip and prevent costly experimental errors and all the rest.
Choose High Quality Pipette Tips for Precision and Accuracy
The first consideration that tends to spring to mind when thinking about which tip type to choose is precision and accuracy.
If there is any batch-to-batch, or within batch, variation in the shape of the pipette tips, then your pipetting will not be precise. This is a build quality and quality control issue, and—as in any manufacturing process—build quality and quality control cost money. So, steering away from cheap tips and buying good quality is generally safer to get minimum variability between tips.
The accuracy of your pipette can be affected if the tip does not fit your particular pipette properly. If there is a poor seal between your pipette barrel and tip, then the drawn-in air can escape and the correct volume of liquid is not aspirated. Therefore, the final volume dispensed is not absolutely correct. Choosing a tip that is a good fit for your pipette can be a tricky business.
Which brings us to the question….
Universal or Pipette-Specific Tips
There is always the option to go for the tips that the pipette manufacturer sells, if available. But, very often, the best option for your pipette and application is to use high-quality universal tips.
These universal tips can be used with most micropipettes on the market. Universal tips are designed to fit securely and tightly around all pipette barrels, which vary slightly in diameter from manufacturer to manufacturer. But of course, all universal tips are not made equal, so you must carefully examine the choices.
Companies that focus specifically on universal tip design closely examined the issues that can arise with pipette tips and developed technologies to overcome them. For example, tips with FlexFit technology are flexible at the proximal end of tip (i.e., closest to the barrel), which gives them a better fit with a wider range of pipette types. Hence, tips with this technology provide greater accuracy and precision.
You can find both universal and pipette-specific tips with all the features discussed below (aerosol barrier, graduated, ergonomic, etc.).
Non-Barrier or Barrier (Filter) Pipette Tips
Non-barrier and barrier tips, or filter tips, are designed for different conditions. Non-barrier tips are designed for everyday lab work. However, if you will be pipetting something that could contaminate your pipette—for example volatile, corrosive, or viscous chemicals—then you’ll want to consider barrier tips to protect your pipette and your samples.
Non-Filter/Non-Barrier or Standard Pipette Tips
You can use non-filter/non-barrier, or standard, pipette tips for many non-sensitive applications. Commonly, laboratories use these tips to load agarose gels, isolate plasmid DNA, and other similar applications. Non-barrier tips are the workhorse in any lab and, as a bonus, usually are the less expensive choice.
These tips come in bulk (i.e., in a bag), pre-racked (i.e., in racks that you can easily place into boxes), or convenient reloads that allow you to easily reuse your racks but avoid the pain of racking bulk tips. While bulk and most reloads are not sterile, you can sterilize them and their storage boxes/racks in the autoclave.
Aerosol Barrier Pipette Tips Prevent PCR Contamination and Help for PCR Positive Controls
Aerosol Barrier tips, also called filter pipette tips, are fitted with a filter inside the proximal part of the tip. The filter protects your pipettes from aerosols and aspirating volatile or viscous solutions into the barrel, all of which can contaminate and damage the pipette. These tips usually come pre-sterilized and DNase/RNase-free. However, “barrier” is a bit of a misnomer for some of these tips. Only certain high-end tips provide a true sealing barrier. Most filters only slow the liquid from entering the pipette barrel.
The filter barrier in these tips make them the choice for sensitive applications, like qPCR. The barrier prevents PCR contamination by stopping sample carryover from the pipette, which will give you more robust results. Also, remember to run your PCR positive control and negative control to find sample carryover.
In addition, filter tips are good ‘training wheels’ for newbies. Many times pipette contamination occurs when a new lab member accidentally aspirates liquid into the pipette itself. It is much easier, and cost effective, to throw away a tip than to send the entire pipette in for repair because liquid is in the piston.
No matter which tip you choose, low-retention is a key feature. Low-retention tips do exactly as the name suggests—retain low levels of liquid. If you’ve ever looked at a standard pipet tip, you might see a little bit of liquid left after dispensing. Low-retention tips reduce this from happening because they have a hydrophobic plastic additive that keeps the liquid from sticking to the inside of the tips.
Nice but Not Necessary Pipette Tip Features
Other features are often incorporated into both standard and barrier tips. These features can help maintain accuracy and even prevent injury. While none of these are strictly necessary, they are nice features to have in a tip.
Graduated tips have measurement markings on their side. These tips work well as a secondary precaution and make it easy to see that the volume reaches the same place on the tip every time. They also serve as reminder to pay attention to your pipetting technique.
Doing repetitive tasks, like pipetting, can cause damage to joints and result in repetitive stress injury (RSI). In light of this, companies have designed ergonomic tips that require lower insertion and ejection forces and, therefore, reduce the risk of RSI. That said, this feature all goes back to good fit. A tip that is specifically designed to fit your pipette properly is by definition an ergonomic tip.
Cost Considerations in Choosing a Pipette Tip
As with most products, you get what you pay for. Well made, properly fitting tips are essential for accuracy, precision, and ease of use. Investing in good quality tips that have been specifically developed for optimal performance is worth the money, unless you are happy with your precision micro-pipette being not-so-precise anymore.
For the other features (graduated markings, barriers, etc.) you should consider whether there is a price for the added feature. If there is an additional cost, chose tips with those features when experimentally necessary. For example, barrier tips are more expensive than non-barrier tips. So, you might want to save the barrier tips for sensitive applications where contamination could wreck your experiment and use the sterile, non-barrier tips for other techniques.
Remember that you can usually request samples from different companies to find what works best for your research.
Your pipette and tip work together to achieve accurate and precise measurements. The variety of tips can be mindboggling. Using this guide will help you choose the correct tip for each application to give you cleaner, more robust results.