The Indispensable Dispenser: The Micropipetter

Distributed by Vanguard International, the Proline is available in five separate models that cover a total volume range of 0.5 µl to 5 ml. Volume is adjusted by turning the piston knob; each incremental change is accompanied by an audible "click" that sets the volume. The digital display window is located on the side of the barrel and is visible during right-handed use. Tip ejection is achieved by depressing a thumb-controlled button on the back of the handle, and a balancing hook on the front provides finger support. Another feature is the inclusion of black tip cones, which are chemical resistant and allow for visualization of a proper seal with the tip. Each unit includes a bench-top mounting holder for pipette storage and a calibration tool. The main advantage of the Proline is its lack of bulk-it is one of the lightest of the pipetters evaluated for this article. Many users mentioned that fact and appreciated the instrument's sleek, ergonomic design. Most also commented that the plunger control was smooth and precise. Some operators (particularly those with smaller hands) did mention that the tip ejection lever was large and dug into the base of their thumbs during routine use. In general, though, the Proline received fairly high marks for its design. Brand Transferpette¨ Distributed by BrandTech Scientific, the Transferpette is available in ten different models spanning the volume range of 0.1 µl to 5 ml. This unit possesses the most unique design among the units tested. The volume adjustment knob is at one end of the handle, a thumb-operated plunger at the top, and a thumb-operated tip ejector lever at the other end of the handle, closest to the thumb. The handle also incorporates a balancing hook to provide finger support. The volume display window, located on the top of the handle, can be read when the pipetter is operated with either hand. Calibration of the unit is simple and does not require any tools. The lower housing is autoclavable, and the entire instrument is also UV-resistant for additional sterilization options or long-term storage in tissue culture hoods. Because of the atypical design, this model, not surprisingly elicited highly varied responses among our users. While its unique handle design was seen as a definite bonus in the multichannel model reviewed previously, the single-channel version felt strangely top-heavy without the manifold to balance it. A few individuals felt this made the unit too unwieldy. Positive remarks were aimed at the piston button and the volume control knob, both of which are very accessible and easy to manipulate, causing no manual fatigue. The fact that the unit is easy to calibrate (no tools are required) was also appreciated. Overall, it was felt that the unusual design of this particular unit would appeal to some researchers, although it might take a period of adjustment. Corning Costar OnePette Costar's single-channel pipetter is offered in four models covering the volume range from 2 to 1000 µl. The feature that distinguishes it from most other models is its volume-setting mechanism: instead of a knob it contains a micrometer dial set in the handle itself, which allows for continuous volume adjustment over the entire range. The current volume display is visible only during right-handed use. Other features include a volume adjustment brake to prevent accidental slippage during use and a finger hook on the front of the handle for balance. The entire instrument is autoclavable for sterilization and is supplied with a tool for in-house calibration. Users commented that the OnePette seems to be a sturdy, utilitarian model-although it lacks design aesthetics-it could withstand a lot of use and abuse. While a bit on the heavy side, it feels well balanced and fits nicely in the hand. The tip ejector button is smooth and is large enough to be easily accessible but not too large that it interferes with pipetting action-a common complaint for instruments of this configuration. Small complaints were directed at the plunger action, which some felt was stiff and may become fatiguing during periods of extended use. The strongest criticisms, however, were directed at the micrometer volume dial, which many judged to be difficult to use and read. Overall, the OnePette was viewed as a very capable instrument but one on which we would have preferred a digital display. Eppendorf Reference 2100 Distributed by Brinkmann, Eppendorf manufacture two pipetters with significantly different designs: the Reference 2000 and the Research 2100. The Reference is available in eight models to cover the range from 0.1 µl to 2.5 ml, while the newer Research comes in seven models covering from 0.1 µl to 5 ml. The main difference between the two instruments is the layout of the handle: while the Reference contains one button that controls aspiration, volume adjustment and tip ejection, the Research contains separate piston and tip ejection buttons. Volume adjustment in both units is accomplished by rotating the plunger button through a series of incremental clicks, and the digital display is visible during use in either hand. The Reference 2000 also has a volume lock to prevent accidental setting changes during measurement. The lower shaft of the Research and the entire Reference are autoclavable. Both units come with a tool for simple calibration by the user. In general, opinion was almost equally split as to which unit was the favorite. Both units received high marks for their innovative design; users appreciated the Eppendorf digital volume display, which was judged to be the easiest to set and read during use. Many individuals commented that instruments felt comfortable to grip-both are light and well balanced. Those that preferred the Research 2100 appreciated the oval-shaped handle and separate tip ejector button. Those that preferred the Reference 2000 liked its volume lock mechanism and complained that the plunger button on the Research 2100 was even higher, which made it difficult for some thumbs to reach comfortably. Overall, though, both the Reference and the Research pipetters were highly regarded by our lab. Gilson Pipetman Over the years, the name Pipetman has become virtually synonymous with pipetter, and to some it still represents the standard against which all others are judged. Distributed by Rainin, this unit is available in eight models to cover the volume range from 0.1 µl to 10 ml. Virtually unchanged since its inception, the design of this venerable lab workhorse has recently undergone some improvements. Continuous volume adjustments can now be made using the plunger button instead of the micrometer knob itself. This makes one-handed volume changes much easier, virtually eliminating interference by gloves. The metal tip ejector has been modified to include a plastic sleeve, making ejector removal easier and replacement more accurate. The digital volume display is located on the front of the handle and is obscured when being used in either hand. The tip ejector button is just under the plunger on the top of the handle. Reaction to the Pipetman seems to fall along generational lines. Consistently, the younger researchers preferred other units, considering the Pipetman bulky, the tip ejector button small and tip removal stiff. Particular criticism was aimed at the plunger spring, which struck many as too strong and therefore likely to fatigue the user after extended use. However, those in the lab who are more seasoned, many of whom had started out at the bench using a Pipetman, still tended to prefer this unit. They cited its virtually indestructible design and dependability as reasons for their preference. Many still consider this the quintessential pipetting instrument. Though it's not the model to please everyone, many individuals still appreciate the old-fashioned design of the Pipetman. Jencons Sealpette The Sealpette appears to be virtually identical to the Biohit Proline in both form and function. It is offered in six models covering the range from 0.5 µl to 5 ml. Volume is adjusted by turning the piston knob through a series of "positive clicks" which prevents accidental setting changes. The digital display is located on the left side of the shaft and is visible during right-handed use. Tip ejection is actuated by depressing a button located on top of the shaft just underneath the plunger. Additional features include a finger hook for increased balance during use and black-tip cones, which allow for verification of a positive tip seal. Each unit includes a calibration tool and complete instructions for in-house servicing. In general, reaction to the Sealpette closely mirrored that of the Proline: it was judged to be a light, easy-to-operate unit that, though ergonomically designed, was perhaps not comfortable in the hands of all users. Criticisms were leveled at the tip ejector button, which protrudes over the handle a bit too far. Labsystems Finnpipette Labsystems has recently updated its entire Finnpipette line, and the single-channel units have benefited from the modifications, as have the multichannel versions. The Finnpipettes are offered in eight models to cover the range from 0.2 µl to 10 ml. In configuration, the instruments closely resemble both the Proline and the Sealpette, with volume adjustments made by turning the plunger knob in discrete increments ("clicks") and digital volume display on the left-hand side of the unit. The pipetter also has a stabilizing "grippy finger rest," which can be used to mount the instrument on the included shelf hanger. This model is fully autoclavable to ensure sterility and can be calibrated by the user with the included tool. Additional features include a soft-touch tip ejection system and "super blow-out" for clean delivery of microvolume-sized drops. Overall user reaction to this model was very positive. The Finnpipette was by far the lightest of the models tested for this review, and its more rounded contours and sleeker profile were judged to be very comfortable. Many users commented that operations like liquid dispensing and tip ejection were performed more smoothly than with other pipettes. The only major complaint seemed to be that for some users, this unit was almost too light and smooth-it gave the impression of being fragile and flimsy, not up to the rigors of everyday use. In general, though, this unit was considered to be a well-designed instrument with many desirable features. National Labnet Labpette The Labpette is available in six different models covering the range from 0.5 µl to 5 ml. The body of the pipette is composed of a low-thermal-conductivity plastic so heat transfer through prolonged use will be kept to a minimum, increasing sample reproducibility. Volume is adjusted by rotating the recessed adjustment wheel directly underneath the plunger; the design of this wheel allows for continuous selection of volume increments and prevents unintentional setting changes during operation. The digital display, located on the side of the handle, is clearly visible during either right- or left-handed use. Additional features include an adjustable tip ejector to allow for accommodation of various tip brands. What sets this instrument apart is the unique layout of the handle: the tip ejector is situated such that the thumb moves laterally between it and the plunger button. When held in this manner, the digital display is clearly readable during use-unobscured by the fingertips as occurs with most other pipetters. While this configuration appealed to most of our users, a few found it difficult at first to adapt to the unusual position of the ejector. In addition, while the piston action was found to be very smooth, tip ejection required more effort than in other units, and not all tips were fully released every time. However, this problem could be corrected by readjusting the ejector shaft. Overall, the Labpette was considered to be an above-average instrument in terms of design and performance. At first glance, the BenchMate appears to be very similar in style to the Gilson Pipetman series. Oxford offers eight models spanning the volume range from 0.2 µl to 10 ml. The volume setting is controlled by turning the plunger knob in continuously adjustable increments, and a locking nut prevents accidental setting changes during measurement. The tip ejection button is located on the front top of the handle, opposite a finger rest for stability. The entire instrument is autoclavable for sterilization and is thermally insulated to prevent body heat from contributing to measurement error. Instructions are included for simple calibration by the user, although no tool is provided. The sleek profile and straightforward layout of this unit found favor with many of our users. About in the middle range of weight for these instruments, the BenchMate was judged to be wellbalanced and comfortable to use, without feeling fragile. Plunger action was strong without being too stiff, and tip ejection was smooth. Volume setting was also hassle- free, and the volume lock mechanism was secure without being too tight. Our researchers did not have much to offer in the way of criticisms. In fact, this model seemed to represent something of a happy medium with the majority of those in our lab: simplicity of form and function combined with ease of use made this a very attractive choice. Rainin supplements the famous Pipetman line with its own new Pipet Plus. Available in seven units covering a volume range of 0.2 µl to 2 ml, it very closely resembles the single- channel Pipetman units both in feel and overall appearance. However, it contains a few cutting-edge features that set it apart from its predecessor, and indeed from all other instruments reviewed for this article. It introduces the idea of "Latch-Mode" pipetting: it contains a magnetic latch mechanism that holds the plunger in the down position, ready for sample pick-up at the end of each pipetting cycle. Thus, when the user wishes to aspirate a sample, he or she only needs to push the magnetic latch as opposed to a plunger. As a result, only one plunger spring is needed to perform the dispensing. There is no blowout step, so the heavy blowout spring is eliminated. Both of these features contribute to significant reduction in thumb stress, thereby reducing the risk of cumulative trauma disorders. Another feature is the addition of an Aspiration Rate Controller (ARC), which is an adjustable valve that controls the uptake speed of the sample. This valve, located on the lower portion of the pipette shaft, allows the user to compensate for variables such as viscosity and shearing. The volume setting is continuous and is adjusted by turning the plunger knob; there is also a volume-locking nut that can be operated with one hand. Tip ejection is controlled with a button on top of the instrument. The digital display is located on the front of the handle and is obscured during right- or left-handed use. Reaction of our users to the Pipet Plus was mixed. The heaviest of the instruments reviewed for this article, it felt unbalanced and unwieldy to some. Other users enjoyed the sturdy appearance and solid feel of this unit. All appreciated the innovative design of the new features, particularly the ARC, which was considered very useful. One individual expressed concern over being able to adapt to the latch-mode mechanism, thinking it might prove a hindrance rather than a benefit. All other aspects of the pipette, including the tip ejection and the lock mechanism, received high marks. In general, the Pipet Plus was regarded by our users as a very promising development in micropipette design that, although it may not be perfect, performed in a favorable manner. In summary, when it comes to micropipetters a significant number of alternatives are available. The collection of instruments evaluated for this review exhibited many different innovative features and specialized functions, each of which will appeal to a subset of users. In reviewing these units, our laboratory found each one to be completely sufficient for routine handling of liquid samples. In terms of operator comfort and ease of use, there was no runaway winner, although the majority of our users favored a few models over the others. Those noted for particular recognition include the Labsystems Finnpipette, for its ergonomic design; Rainin's Pipet Plus, for its innovative new features; and the Oxford BenchMate, for its overall value as a well-built, simple, dependable instrument. Also receiving high marks were both of Eppendorf's units: the Reference 2000 and the Research 2100. In conducting these evaluations, we have tried to remain as objective as possible, recognizing that each individual will have his or her own tastes and preferences. Nevertheless, there is a pipetter on the market to suit everyone. We hope this review will serve as a guide, illustrating the many choices available to the lab researcher as a consumer. The author can be reached at ktmiller@ucsd.edu. Chart 1

The Indispensable Dispenser: The Micropipetter

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Katharine Miller

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November 1997

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