Over and Over: LabConsumer Tests Nine Repetitive Pipetters

Date: April 27, 1998 Author: Katharine Miller Repetitive Pipetters Survey Results In today's fast-paced, competitive world of biomedical research there is growing demand for products that increase sample throughput, either through automation or by operator efficiency. Manufacturers of experimental equipment have responded by constantly redesigning and refining their instruments, incorporating the latest technological advances with consumer input. Even the simplest, most ubiquitous laboratory tools, such as the pipetter, have undergone this evolution. As discussed in previous articles, not only are many different styles of the typical single-channel mechanical pipetter available, but various multichannel and electronic models have been developed as well--each of which can contribute dramatically to productivity and throughput. In this current installment we consider yet another permutation of the liquid delivery system: the "repetitive" pipetter. The Jencons Repette The primary function of the repetitive pipetter is evident in its name: it is designed to repetitively dispense a large number of liquid aliquots of the same volume with minimal need for refilling. The majority of repetitive units adhere to the same basic design. A cylindrical shaft is held vertically in the hand as is any other pipetter, and disposable plastic tips are used to deliver the sample. The nature of these tips is what distinguishes repetitives from other pipetters; they are actually syringes that can be filled with sufficient liquid for several actuations of the plunger. Syringes come in a variety of sizes, each capable of a range of aliquot volumes. Typically the syringe is inserted into the lower portion of the shaft, where the plunger is locked into place by a pull-down lever. A dial located at the top of the handle is used to select the volume of the aliquot as a function of the size of syringe being used. The syringe is then filled by immersing the tip in the liquid and slowly pushing up on the filling lever located on the side of the shaft. Aliquots are dispensed by pressing down on the pipetting lever or button near the top of the handle. The pipette will continue to deliver precise aliquots until the liquid level falls below the necessary volume in the syringe reservoir, when it stops. At this point the syringe can be either refilled as described or discarded by pulling up on the locking lever. Clearly, use of one of these instruments can significantly reduce the amount of hands-on time required for an experiment as compared to an ordinary pipetter. BRANDHandyStep® Pipette The following article is a review of several currently available repetitive pipetters. In this evaluation, many areas of concern to the operator were considered: ergonomics and ease of use, cost of the pipetter, durability, special features, and so on. Particular attention was paid to how well the unit succeeded in its primary function of simplifying the task of repetitive pipetting. The section covering each model begins with a brief physical description, although as these instruments are, for the most part, very similar in layout, this description is generally restricted to what is unique about a particular model. Some subjective comments of the unit are then offered that represent views expressed by two groups asked to evaluate the pipettes after hands-on use: (1) nine researchers from an independent biotechnology company (including the author) and (2) attendees of the laboratory trade show Pittcon '98 (New Orleans, La., March 2 and 3). All instruments are critiqued and potential usage problems analyzed. It is important to bear in mind that these comments reflect the preferences of individuals and are not consensus opinion unless so noted. Two dispensing pipetters were not reviewed in this article; the BRAND HandyStep® repeating pipette from BrandTech Scientific and the Jencons Repette, introduced by Jencons at Pittcon '98. Specifications for these two pipetters can be found in the comparison table. Eppendorf® Repeater® Plus and Repeater® Pipette Distributed by Brinkmann Instruments, the Eppendorf Repeater Pipette is the original repetitive pipetting instrument, and its design is the one from which most other repetitive units have evolved. It conforms to the standard configuration described (having defined it), with a filling lever, dispensing lever, and pull-down syringe locking clamp. The vertical volume-selection dial has five positions, and on position #1 the instrument can deliver a maximum of 48 aliquots from a single syringe. The Repeater Pipette is designed to be used with Eppendorf Combitips® and Combitip® Plus tips but can accept "generic" tips (modeled after the Combitips). Combitips are available in bulk, sterile, or Eppendorf Biopur packaging in the following standard sizes: 0.05, 0.1, 0.2, 0.5, 1.0, 1.25, 2.5, 5.0, 10.0, 12.5, 25, and 50 ml. This range of tips allows for delivery of 37 different aliquot volumes between 1.0 µl and 5.0 ml. An adapter is required for use with the 25 and 50 ml tips (provided with each instrument). Only the 0.05 ml Combitip is autoclavable. Many of our users were already very familiar with the Repeater Pipette. In the trade show survey, Eppendorf was listed as the most recognized pipetter brand, and the Repeater Pipette had the highest frequency of current use. Our participants found this unit easy to fill, and insertion and removal of syringes were simple as well. A common criticism focused on the relative placement of the filling and dispensing levers--more than one individual commented that it was easy to mistakenly press down on the filling lever while trying to deliver an aliquot and instead empty the entire syringe. Others found the handle slightly uncomfortable to grip for extended periods of time. Aside from these minor complaints, the Repeater Pipette was a solid performer, well received by those surveyed. Eppendorf's second offering (also distributed through Brinkmann Instruments) is distinguished from its predecessor by some unique, innovative features. While its configuration is virtually identical to that of the Repeater Pipette, the Repeater Plus Pipette is semi-electronic, containing a battery-operated digital display that automatically recognizes the size of the CombitipTM Plus tip that is inserted and displays the volume of aliquot delivered at each volume setting for that tip. (The battery has a two-year life and is not in use unless a tip is inserted.) The volume-selection dial itself is also different, containing 20 settings in increments of 0.5 from 0.5 to 10. This feature allows for delivery of 104 different aliquot volumes between 1.0 µl and 10.0 ml. Up to 100 aliquots can be dispensed from a single syringe filling at a volume setting of 0.5. The third new feature is the inclusion of tip-ejection buttons instead of a locking lever, which allows for hands-free ejection of used tips. The Repeater Plus Pipette accepts only Combitip Plus tips, available in bulk, sterile, and Eppendorf Biopur packaging in 0.1, 0.2, 0.5, 1.0, 2.5, 5, 10, and 50 ml volumes. An adapter is required for use with 50 ml tips (included). The adapter is different from the adapter required for the Repeater Pipette when using 25 and 50 ml Combitips. None of the Combitip Plus tips are autoclavable. Our users had many positive comments about the Repeater Plus. Many remarked that it was even easier to fill syringes than with the Repeater and that the dispensing action was smoother. Participants appreciated the syringe locking buttons, citing the desirability of being able to eject tips without touching them. The increased range of deliverable volumes was also seen as an advantage. The only criticisms of this unit concerned the aforementioned relative placement of the filling and dispensing levers and its bulk--due to its battery pack, the Repeater Plus Pipette was one of the heaviest units in our survey. Overall, though, our respondents felt this model represented a significant improvement of an already respected product. Labsystems Finnpipette Stepper As its name would indicate, Labsystems' repetitive pipetter contains many of the ergonomic features of the company's Finnpipette line of single-channel instruments. The Finnpipette Stepper is the lightest of the units evaluated here and incorporates Labsystems' trademark "grippy finger rest" for maintaining balance and correct position during operation. In the standard mode it contains a vertical five-position volume dial and thumb-operated levers for both filling and dispensing, although it has no syringe lock. The method of syringe filling is significantly different, however--the filling lever is depressed, not raised as for all other models considered. The Finnpipette Stepper accepts only Finntip Stepper tips, available in bulk and presterilized in 0.5, 1.25, 2.5, 5.0, 12.5, 25, and 50 ml volumes. The included adapter is required for use with the 25 and 50 ml syringes. The pipetter is capable of dispensing up to 44 aliquots on the lowest volume setting, and 24 different volumes can be selected in the range from 10.0 µl to 5.0 ml. A volume chart, cross-referencing syringe size with dial setting and aliquot volume, is printed on the side of the handle. The Finnpipette received mixed reviews from our panel. While some users liked the lightness of the unit and found it comfortable to hold, others thought it felt too light and fragile. The operation of the dispensing trigger was judged to be very smooth and nonfatiguing. The reverse orientation of the syringe-filling mechanism was generally received favorably because it allowed the tip to be easily filled using one hand. However, several individuals reported difficulty inserting and removing tips. Overall, the Finnpipette Stepper appealed to a subset of our users, who would definitely consider buying it on the strength of its features and the Labsystems name. National Labnet Labpette The Labpette R is very closely modeled after the standard repetitive design with a few subtle modifications. This pipetter is similar in design to the Ritter-Med Ripette. The five-position volume-selection dial is placed horizontally in the top of the handle, just beneath the dispensing button, which is much like a traditional pipette plunger. There is also the usual filling lever in the pipette shaft and a syringe locking clamp. Up to 48 aliquots can be delivered from a single filling on setting #1, and a total of 29 different aliquot volumes are possible spanning 1.0 µl to 5.0 ml. The Labpette R will accept universal-style syringes and an adapter is included for use with 25 and 50 ml syringes. The instrument also has a volume chart located on the pipette shaft. Although this model was unfamiliar to our users, and National Labnet's name recognition was not ranked very high in the trade show survey, the Labpette R fared well in the evaluations. Many users found the rounded, slimmer handle more comfortable than that of the Eppendorf Repeater Pipette. Several reviewers also commented that the volume dial was easier to adjust and the piston action smooth and fatigue-free. The volume conversion table was universally appreciated. Minor criticisms were aimed at the slight difficulty in the positioning of syringes and, for a few individuals, the tendency of the fill lever to press into the palm during dispensing. In general, though, the Labpette R was found to be unusually straightforward, a capable unit likely to find favor with a large population of researchers. The Nichimate Stepper The Nichimate Stepper is similar in appearance to the Oxford line of standard pipetters, also manufactured by Nichiryo. This instrument follows the universal repetitive pipette design with a few slight modifications: instead of a dispensing lever there is a button at the top of the unit that also incorporates the five-position volume-adjustment dial. There is a filling lever on the side of the handle and a syringe locking clamp at the base. The Stepper can deliver aliquots of 29 different volumes between 1.0 µl and 5.0 ml and dispenses a maximum of 48 aliquots at the lowest dial setting. It will accept generic syringes, and Nichiryo offers tips in the standard eight sizes. An adapter is provided for the 25 and 50 ml syringes. The Nichiryo name was virtually unrecognized by our respondents, although many were familiar with the "Oxford-like" styling. This unit received similar comments to those of the Labpette R and Ripette. It was termed easy to use, with a comfortable grip and smooth filling action. Many liked the handle, which is noticeably slimmer than those of other units. The most common complaint involved the volume-selection dial, which is small and somewhat difficult to operate, particularly for those with large fingers. The consensus of our participants was that the Nichimate Stepper, much like the Labpette R and Ripette, is a capable, dependable instrument that is generally comfortable and easy to use. Oxford Model 8100 Also manufactured by Nichiryo, the Model 8100 is distributed by Oxford under its private label. It resembles a slightly less streamlined version of the Nichimate Stepper, with the same basic layout of filling lever, finger support hook, dispensing button, and five-position selection dial. In contrast, it does not have a syringe locking clamp and does have a volume conversion chart printed on the handle. Although the 8100 covers the same aliquot range as many of the other instruments reviewed here (1.0 µl to 5.0 ml), the volumes it delivers are slightly different due to the syringes it accepts: 0.06, 0.6, 1.5, 3, 6, 15, and 60 ml. Using these syringes (provided by Oxford--the 8100 will not accept generic tips), the unit will deliver 27 different volumes and has a capacity of 58 aliquots at dial setting #1. Only the 60 ml syringe requires an adapter (included). What is perhaps most interesting is that this unit is the only instrument reviewed that provides a range of autoclavable syringes. The Oxford Model 8100 was familiar to some of our respondents, being second only to Eppendorf in current use and to both Eppendorf and Rainin/Gilson in name recognition. Due to the similarities in design, the comments the Model 8100 received were reminiscent of those for the Nichimate Stepper: "syringes very easy to insert," "light, comfortable handle," "I like the volume table," "the volume knob is difficult to adjust." Though some recognized the appeal of autoclavable syringes, others saw the incompatibility of generic tips as a drawback. Overall, the Oxford Model 8100 was well received for its sensible, logical design and operation. Gilson/Rainin Distriman Manufactured by Gilson and sold through Rainin Instrument Company, the Distriman has the distinction of being the only continuously adjustable repetitive pipette in this review. This feature means that there are essentially an unlimited number of aliquot volume settings possible in the range of 1.0 µl to 1.25 ml covered by the instrument. The Distriman looks very similar to the famous Pipetman and is structured along the lines of the standard repetitive pipetter. The volumeter display is located on the pipette body. A black adjustment ring located under the dispensing button controls the digital volumeter readout and automatically locks down during delivery. There is no syringe clamp. The Distriman accepts Gilson Distritips (available in 125 ml, 1,250 ml, and 12.5 ml volumes) and can deliver a maximum of 100 aliquots from a single filling. No adapter is required. This instrument was already familiar to some of our users. Many implicitly trusted the Rainin/Gilson label, a brand name that received high recognition scores in the trade show survey. Some appreciated the dispensing button, which was considered to be easier to use than a lever. The grip was judged to be comfortable as well. Although a number of individuals approved of the capacity to select any aliquot volume, others did not like the volumeter setting mechanism, claiming it was "too confusing." Another common complaint concerned syringe insertion and removal, which some unpracticed individuals considered "tricky." In general, the Distriman was found to be a unique model with unusual features to appeal to a variety of users and was highly favored by Pittcon reviewers. Ritter-Med Ripette As mentioned previously, the Ritter-Med Ripette and the Labpette R from National Labnet are strikingly similar and share many of the same features. The Ritter-Med Ripette is closely modeled after the standard repetitive pipette design with some small modifications. The five-position volume-selection dial is placed horizontally in the top of the pipette handle, just beneath the dispensing button, similar to a traditional pipette plunger. The Ripette's filling lever is in the pipette shaft, and a locking clamp holds syringes in place. Up to 48 aliquots can be delivered from a single filling on setting #1, and a total of 29 different aliquot volumes are possible, spanning 1.0 µl to 5.0 ml. While, the Ripette is compatible with universal-style syringes, Ritter-Med offers Ritips in bulk, sterile, and pyrogen-free packaging available in eight standard sizes. Included with the instrument are adapters for use with the 25 and 50 ml syringes. A volume chart is placed on the shaft of the Ripette. Unfamiliar to our users, the Ripette earned high marks in both evaluations. Similar to the Labpette R, people favored the rounded, slimmer handle and found it more comfortable than that of the Eppendorf Repeater Pipette. Several participants noted the volume dial was easy to adjust and the piston action was fatigue-free and smooth. Having the volume dial on the pipetter shaft was a feature appreciated by all. Minor criticisms were targeted at the positioning of syringes, which some found difficult, and for a few individuals, the tendency of the fill lever to press into the palm during dispensing. In the end, however, users found the Ripette to be a straightforward and capable instrument apt to be well-liked by a large population of researchers. The Step-Pette This instrument, manufactured for Wheaton by Socorex (Switzerland), has a truly unique configuration that sets it apart from the other instruments described here. The Step-Pette is shaped like the #7, with the point of the 7 facing away from the user's palm. Along the back of the handle lies the dispensing trigger, which is activated by depressing with the fingertips. A syringe is filled by pulling up on the finger loop of the piston rod, which comes out of the top of the handle. Aliquot volume is selected by attaching one of three different volume-setting knobs (included) to the handle. These knobs contain a micrometer-like dial that can be adjusted though numerous increments and are color-coded to the three types of syringes accepted by the unit: 0.75, 3.75, and 37.5 ml. These syringes must be obtained through Wheaton; the Step-Pette will not accept generic syringes. There is no syringe locking clamp, and the 37.5 ml tip must be used with the included adapter. The Step-Pette generated more heated discussion among our respondents that any other instrument in this review. Accolades were given for the finger loop, which made it exceptionally easy to fill even the large volume syringe. Some also noted the ease with which tips were inserted and removed. However, many complained that the overall design was bulky and uncomfortable to use, the trigger was stiff and fatiguing, and the volume knobs are difficult to remove. A few researchers voiced concerns over the way the whole instrument "rocked back" when the trigger was depressed, an issue when tip control is important. One individual pointed out that with three detachable volume knobs, the potential exists to lose one of them in the laboratory. While the Step-Pette was acknowledged to possess many attractive features, its overall design did not find favor with the majority of our reviewers; however, some Pittcon reviewers favored this device. In summary, when it comes to repetitive pipetters, a significant number of alternatives are available. All of our respondents were amazed at just how many manufacturers offer repetitive models. In reviewing these units, our participants found each one to be completely sufficient for routine handling of liquid samples. At the final tally there was no clear winner, although the majority of our users favored a few models above the others. Those noted for particular recognition include the Eppendorf Repeater Plus Pipette, for its useful combination of innovative features, and the Ritter-Med Ripette, with its low list price, for its exceptional value as a well-built, simple, dependable instrument. 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 repeating pipetter/dispenser on the market to suit everyone. Hopefully 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@chromagen.com Repetitive Pipetters Survey Results

Over and Over: LabConsumer Tests Nine Repetitive Pipetters

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