A pipette is all about consistent performance. A scientist expects a pipette to aspirate and dispense the intended volumes thousands and thousands and thousands of times. Plus, a pipette can be used with a range of liquids—some of them more pipette-friendly than others—and operated by multiple users. Still, scientists expect steady performance, but that can only be ensured with proper maintenance and calibration.
Joni Åke, product manager at Sartorius, talked about a two-stage program. The first part is cleaning and maintenance, and the second part is calibration. For the required amount of cleaning and maintenance, “it really comes down to what you actually do in the lab—what kind of liquids you use, in some cases how many users you have per pipette and so on,” he said. “If you use the pipette for water-like liquids, it probably won’t get really dirty, and you don’t need to worry about cleaning that often, but if you use viscous liquids, like glycerol or something that foams really easily, the risk for contaminating or making the pipette dirty is higher.” Consequently, Åke recommends a risk-based approach to cleaning and maintenance.
Keep it clean
For a general rule of thumb, pipettes should be cleaned on a weekly or monthly schedule. At the very least, clean the outside with an ethanol-moistened cloth and then wipe off with a lint-free cloth. Cleaning a really dirty pipette might require a professional. To ensure fresh pipettes in a lab, “it might be a good idea to have someone look after them and make sure that they’re cleaned often enough,” Åke suggested.
Image: Accurate pipetting depends on regular cleaning, maintenance and calibration. Image courtesy of Sartorius.
If something feels off, like a plunger taking more force than usual, the inside also needs to be cleaned. The lower parts—cylinder, piston, and tip ejector—can be disassembled and cleaned. After lubricating and assembling, a pipette’s performance must be checked.
If something in the handle needs cleaning or repair, it’s time to send out a pipette for repair. Most labs can’t even open the handle, because “you need special tools,” Åke pointed out.
Most of all, scientists should stick to the schedule. “Make sure to do the maintenance, instead of waiting for a pipette to be broken,” said Melinda Gold, product manager at Artel. “Pipettes are subject to wear and tear even under normal conditions.”
Beyond wiping down the outside of a pipette, even minor disassembly takes some know-how. “Training is important—knowing what part comes apart and what doesn’t,” said Kaziya Lee, applications specialist at Artel. It even comes in handy to know how much oomph to add in certain disassembly steps. “Removing the tip ejector can take more force than you might think,” Lee noted.
Looking after leaks
“By far the most common cause of pipette mechanical failure is leaks,” said Akbar Anwari, marketing manager at BrandTech Scientific. “Typically, most people think of pipette leaks as occurring between the piston and seal—when the piston and/or seal is dirty or damaged—but leaks also occur between the tip and tip cone when a poorly fitting tip is used.”
Even a tiny leak reduces the performance of a pipette, and a small problem might be hard to see. “These leaks—though often too small to be detected by the eye—are enough to reduce the amount of pipetted liquid, affecting accuracy of the pipetted volume,” Anwari said. “I would recommend routinely verifying the instrument, as well as the tips used with the instrument, with a leak tester.”
Keep it calibrated
For in-the-lab calibration, a scientist weighs a series of pipetted volumes. Anwari recommended 100, 50, and 10% of a pipette’s capacity. He noted, “Each testing volume needs to be measured enough times to be statistically significant—at least five, but preferably ten times.” For gathering the data, Anwari said, “BrandTech offers a free Windows program that can be interfaced directly with your balance to eliminate transcription error and does all the math for you, including the conversion from mass to volume—something often missed by novices.” If needed, adjustments can then be made, and the pipette should be retested to verify its performance.
Another method for in-house calibration that scientists can use is the Artel PCS Pipette Calibration System. The PCS uses a photometric method to provide a 10-data-point calibration in less than three minutes, and it is immune to environmental conditions.
Some larger organizations have the needed environment and equipment—controlled temperature and humidity, 6-decimal place analytical balances and moisture traps and so on—along with trained experts to perform pipette calibrations, but most facilities cannot perform all of the necessary testing.
When sending out a pipette for any service, confirm what it entails. As Lee asked: “Do they change the replacement parts every time or just inspect them?” Plus, Åke noted that “there are some differences in what pipette service entails.” As he said, “Some providers might just clean a pipette from the outside and check calibration in two volumes and three repetitions.” He added, “It depends what the customers asks for.”
Like cleaning, pipette calibration should be on a schedule. For most R&D labs, the experts interviewed here suggest once or twice a year, but some labs require more frequent service. “Select the appropriate calibration schedule for your needs,” Lee said. “Our general recommendation is every six months, but more stringent environments might require monthly calibrations or more.”
In the end, keeping a pipette performing as expected depends entirely on how it’s used and how precise it needs to be. One thing applies to all pipettes: They need attention. After months and years of pipetting—accumulating an enormous number of actions—no product works like new without scheduled care. From cleaning to calibration and part replacements and more, only a pipette that gets the proper treatment can provide the desired performance. With the amount of pipetting performed in academic and industrial labs, scientists can’t afford a faulty device. If pipetting is inconsistent, so are the results of entire experiments.