Editorial Article
Wednesday April 28, 2010
by Jeffrey M. Perkel
Is the most frequently used piece of lab equipment also the least considered? In a sense, yes.
No hardware gets more of a workout in molecular biology labs than the pipette. And yet, for many researchers, their purchase is an afterthought. If they used Rainin pipettes as postdocs, they tend to purchase Rainin pipettes as assistant professors.
"It's one of those things that are used pretty much every day," says Jim Petrek, chief technology officer at Rainin. "It's like a pen, it's a very personal thing you trust and rely on."
Mylène Louicellier, product marketing manager at Gilson SAS, compares the pipette to an essential kitchen tool. "It's like a knife in the kitchen," she says. "You don't think about the knife when you cook, but you cannot cook without it."
The reality, says Petrek, is that "people get comfortable" with their pipettes—as with a pen or a knife—"and there's discomfort in switching." As a result, researchers "need a good reason to switch," and manufacturers like Rainin and its competitors have been working to provide one.
Today, says Ali Sorg, liquid handling product manager for Eppendorf North America, the "important buzzwords" in the micropipette marketplace are ergonomics, accuracy, and precision.
According to Sorg, accuracy and precision both refer to the amount of scatter in volume a pipette delivers. Accuracy is a measure of how close the volume the pipette delivers is to the desired volume, whereas precision relates to how closely each presumably identical liquid transfer is to another. Think about trying to hit a bullseye with five darts, Sorg explains. If all five darts hit the bullseye, you are both accurate and precise. If all five darts hit the same point, but not the bullseye, you are precise but not accurate. In the pipetting world, that may mean you have good technique, but your pipette might be out of calibration. In contrast, if the darts are scattered across the board, you are neither accurate nor precise -- a problem of both calibration and technique.
The documentation for Hamilton's SoftGrip 10-100 uL Adjustable Volume Pipette lists its accuracy for dispensing 100 uL as +/- 0.6% and its precision as +0.15%. That means, says Donald Robertson, Hamilton technical sales representative, that when the pipette's dial is set to 100 uL, it will reliably dispense between 94 and 106 uL. "For a handheld air displacement instrument, that's a pretty good number," he says.
Most name-brand pipettes boast reasonably similar specifications for precision and accuracy, says Petrek, especially when you take into account that users often do not reach the precision achieved in performance testing because each researcher uses the pipettes a little differently—they may not be consistent in their technique, for instance, or they may use third-party (as opposed to manufacturer-recommended) tips in their experiments.
Pipettes do differ substantially when it comes to ergonomics, however.
Fundamentally, a micropipette isn't much different from the hollow reeds or straws children play with in restaurants—insert a straw into a glass of water, plug the top with your finger, and you have a crude, albeit imprecise, liquid transfer device, says Robertson.
Most modern manual micropipettes work more or less the same way, and maintain that same classic "axial" configuration, with a tip at the bottom, plunger and volume controls at the top.
The problem is, for people who use pipettes for hours each day, day in and day out, that familiar configuration can cause repetitive stress injuries. Pipettes are relatively heavy, for instance, and require significant forces to load and eject tips, and to aspirate and dispense liquids. Those problems can affect users' hands, wrists, arms, even their necks—and the problems only intensify when using multichannel pipettes (where, for instance, ejection force multiplies).
"If a worker goes out on medical leave for repetitive stress injuries, it can cost a company $35,000 in time off, medical expenses, and so on," says Sorg.
New ergonomic pipettes attempt to address some or all of these problems, for instance by using lighter weight materials, low-force plungers, and spring-loaded tip attachment and ejection systems.
Eppendorf's manual pipettes, for instance, weigh 80 gm (compared to 115-140 gm for older models) and require just 3.6N of operational force, as compared to 10-15N for more traditional pipettes, says Sorg.
Tip insertion and ejection, by all accounts, impose perhaps the most significant forces in pipetting. An 8- or 12-channel multipipettor, for instance, can require 22 lbs or more of ejection force, says David Metrena, vice president of sales and marketing at VistaLab Technologies. The company's Ovation pipettes feature a spring-powered tip-loading system that makes tip ejection far less ergonomically stressful, he says.
Similarly, Rainin's new LTS ("LiteTouch System") pipettes feature a new shaft and tip design that reduces tip ejection force from about 4kg per tip to 0.6kg, says Petrek. According to Petrek, "the pipette tip seal area is cylindrical with a focused seal, and when you put your shaft in the tip, there's a hard stop in the tip. You don't have to bang it, and it goes on with the same amount of force every time."
New pipette designs also take into account the pipette user's grip. "Anybody that squeezes something for four-to-five hours a day for multiple years is going to develop carpal tunnel problems," says Robertson. Hamilton's SoftGrip pipettes feature a large hilt or handle on top of the pipette body to support the pipette's weight on the user's hand so that it won't slip, and a "slightly textured body designed to be held loosely, says Robertson. Instead of tightly gripping the device like an ice pick, Robertson advises users to close their hands, "but not so tight you cannot still read the word 'Hamilton'" on the barrel.
Perhaps no company has worked harder to advance ergonomics in pipette design than VistaLab Technologies.
"The shape of the [company's Ovation] pipette came from some studies that were done about 10 years ago where we brought in ergonomists who had nothing to do with the lab and showed them a typical pipetting station," says Metrena. Based on their recommendations, he says, "We changed the traditional axial pipette into a pipette whose form is much more comfortable and more correct with the human anatomy." That design is completely novel in the world of micropipettes, looking less like a pipettor than a plant spritzer.
According to Metrena, the Ovation pipettes focus not on any one aspect of ergonomy, but on the whole package. It features a low-force plunger and spring-loaded tip acquisition and ejection, as well as a digital volume-control system with five preset volumes (to avoid turning the volume-control knob between uses). But, most significantly, the Ovation is designed to keep the user's palm facing down, rather than to the side, and to keep the user's elbows closer to the body.
"The more you rotate your wrist palms up, the more stress you put on your carpal tunnel," says Metrena. "[The Ovation] keeps your elbow by your side instead of the 'chicken wing' posture of traditional pipettes."
Manufacturers have come up with many small ways to make this most universal of lab tools easier to use. For instance, Hamilton pipettes have the volume adjustment ring down on the lower body of their pipettes so that it cannot accidentally be adjusted mid-use. Thermo Fisher Scientific focuses on what product manager Tero Pasanen calls "vision ergonomics"—that is, making the volume control dial easy to read.
There are other features users should consider, as well, such as ease of maintenance. Thermo Fisher Scientific's Finnpipette F1 series features a silver-infused antimicrobial surface, while its F2 series pipettes are fully autoclavable. Hamilton's pipettes feature a universal calibration key, which fits all Hamilton SoftGrip pipettes, that simplifies the process of keeping the system calibrated.
Most manufacturers also offer both single- and multi-channel pipettes (e.g., 8 or 12 tips), as well as manual and digital pipettes.
Digital pipettes, like Gilson's Pipetman M, offer the advantages of being programmable, not requiring the user to dial in each new volume—and of providing functions not seen in manual pipettes, such as repeat pipetting (that is, aspirating, say, 1000 uL and dispensing 100 uL) and sample mixing.
Pasanen recommends electronic pipettes for users who do more than about an hour of pipetting per day, or (using multichannel pipettors) fill more than five or 10 microtiter plates per day. By switching to digital, he says, "you can do all the things you do with a manual pipette, but you don't have to use your thumb to move the pistons, because there's a motor."
And then there are the tips. Some pipettes can use basically any standard yellow or blue tip. Others, like Rainin's LTS pipettors, require dedicated consumables. Still, for best results, says Metrena, consider using the manufacturer's tips, if possible.
"You should look at pipetting like a total system, such as a [chemical] analyzer," he says. "You can't slap just any old tip on and hope to get the precision and accuracy specifications the manufacturer claims. The published specs are done using their own tips."