Best practices dictate that pipettes undergo preventive maintenance and calibration at least once per year. Calibration involves dispensing set volumes of a liquid, usually water, into the weighing pan of a calibrated balance. Service personnel correct for temperature, humidity, and atmospheric pressure, and then compare the expected weight to the actual weight. Among the numerous service options are end-user, in-house instrument service groups, third-party maintenance organizations, and the original manufacturer. All have their benefits and drawbacks.
Small, independent service providers are numerous and focus on academic customers within a relatively small geographic area. Regardless of their size, service organizations work either through “depot” arrangements (pipettes are boxed and shipped to the servicer) or on-site. Servicers generally do not require a minimum number of devices for depot service, but all have requirements for on-site service.
The fly in the ointment for third-party servicing in general is the electronic pipette. Although electronic pipettes comprise just 7–8 percent of all pipettes in use today, electronic models are the fastest-growing segment of pipette products. Multichannel pipettes make up approximately 20 percent of sales, while standard, single-channel piston and o-ring devices comprise about 70 percent of the market.
“Most service providers can easily service standard pipettes,” says Joe Fredette, product director for liquid handling and consumables at Thermo Fisher Scientific (Hudson, NH). Thermo Fisher and other manufacturers provide calibration and service instructions freely to users who choose to service their own pipettes. But electronic pipettes, which contain printed circuit boards and onboard logic for storing methods, can be challenging. “They require a professional service provider,” Mr. Fredette adds.
Users who service their own pipettes have several options. A&D Weighing (San Jose, CA) sells a dedicated balance for pipette testing that includes accessories for servicing pipettes. The main components are software and an evaporation trap to ensure that very low liquid volumes do not evaporate or pick up moisture from the air. A&D also sells a leak tester that induces a vacuum to detect leaks in pipette seals, pistons, or o-rings.
“Any organization can perform its own calibration and routine service. Whether they are actually interested [in doing so] is another matter,” observes Markus Jansons, weighing products manager at A&D. “You need to have a relatively large number of pipettes to justify dedicating equipment and personnel to pipette calibration.”
Remember, though, that pipetting is susceptible to end-user technique, and what holds for pipetting in general is doubly true for pipette calibration.
Due to issues of time and convenience, demand is rising for servicing pipettes on the customers’ premises, but hardcore metrologists protest that control over environmental conditions is impossible. Rigorous depot calibrations take place in environmentally controlled rooms. “Saying that you’re not getting a true calibration is a bit hardline,” says Mr. Fredette. “But in fact, what many users receive on-site is not a calibration, but a service check.”
Like most large manufacturers with service businesses, Thermo Fisher performs on-site service using a NISTtraceable balance that is calibrated twice yearly. It also provides GMP/ GLP-compliant calibration reports, which are required in the pharmaceutical industry and are increasingly favored by academic labs as well. An ISO 17025 calibration, which entails 10 measurements per volume at three different volumes (versus four measurements at two volumes), represents the pinnacle of calibration but also doubles the cost.
What goes wrong
The reason pipettes require regular maintenance is that they are mechanical devices that are, in many instances, used constantly. Volatile acids, bases, and organic solvents wreak havoc on the seals, o-rings, and metallic components.
“Stainless steel pistons oxidize and suffer corrosion under conditions of harsh use,” notes Jesse Cassidy, product manager for liquid handling at Eppendorf North America (Hauppaugue, NY). “The state of the piston holds great implications for a pipette’s accuracy and longevity.”
Eppendorf has replaced stainless steel in its pistons on some models with Fortron®, a high-performance thermoplastic developed by Fortron Industries (Florence, KY). The strong polyphenylene sulfide plastic possesses high resistance to chemicals, oxidation, and temperatures as high as 200°C.
The company has introduced another interesting calibration-related feature that it calls “secondary adjustment.” This is useful when, for whatever reason, a pipette is calibrated to the mass of a solvent other than water. Through secondary adjustment, calibrators can dial in a value for the nonaqueous solvent, which applies both to calibration and subsequent use with that fluid.
Complex design, complex maintenance
In our last survey on laboratory pipettes, published in January 2011, 85 percent of 464 users cited ease of use and ergonomics as key factors in purchase decisions. Ergonomics followed closely behind accuracy, performance, durability, and availability of consumables.
Ergonomics is the key behind VistaLab Technologies’ (Brewster, NY) radical pipette design. “We think the world has seen enough stick pipettes,” says VP of engineering Jeff Calhoun. VistaLab’s designs resemble a staple gun or pistol.
Servicing the company’s Ovation line of single-channel and multichannel pipettes can be somewhat challenging, as the devices are mostly electronic and their layouts are unfamiliar.
“As the manufacturer, we’d like to see all our pipettes come back here for service and calibration, because nobody’s better at servicing them than we are,” Mr. Calhoun tells Lab Manager Magazine. VistaLab maintains five certified repair facilities, with locations in Europe, Asia, and Australia, as well as one site (VistaLab itself) in the U.S.
The company has a training program for third-party service organizations, and sells them replacement parts as needed. “We’re very flexible about helping outside calibration labs service our pipettes,” Mr. Calhoun says. “We completely support our customers as much as possible.” He estimates that training enables service organizations to handle about 90 percent of problems encountered with Ovation pipettes.
For additional resources on pipettes, including useful articles and a list of manufacturers, visit www.labmanager.com/pipettes.