Special Delivery: New and exotic products for specialized pipetting

Table of Specialty Pipettors Table of Specialty Pipette Tips Specialty pipette tips are like the high-performance tires on a formula-one race car. While most people would imagine that fuel injectors, turbochargers, or transmissions are the fundamental elements of an advanced racing machine, few people consider the importance of tires, when in fact, according to authorities on racing, the whole purpose behind the design of an automobile is to create an environment where the tires contact the pavement. This might seem like the tail wagging the dog, but in the final analysis, it's the tires, perhaps the least sophisticated component of the vehicle, that demand the greatest attention. Pipette tips are the tires on a pipettor. You might have the best pipettor that money can buy, with a digital display, active memory, and 10 different operation modes, but if you're using the wrong pipette tip to deliver the sample, it's the same as riding on rims. LabSystems' Finnpipette® 384 A great variety of pipette tips has been developed in recent years for electrophoresis and PCR. These range from the rough-and-ready wide-bore tips--the pipetting equivalent of snow tires--to the very delicate ultramicro tips. Each of these has been designed to correct a specific problem or fulfill an important need that has arisen from the revolution in molecular biology. One of the important issues relative to pipette tips is knowing what kind of bore diameter to use. Pipette tips with greater bore size permit the pipetting of high molecular weight DNA without shearing. These are useful for pipetting mammalian cells or viscous samples. On the other hand, a wider bore can be affected by changes in barometric pressure that can lead to calibration problems. These larger tips are sometimes recommended for use at specific temperatures to ensure consistent performance. Alternatively, pipette tips with smaller bore diameters are not readily affected by temperature and pressure and can be used inside narrow gauge tubes and sequence gel wells. However, the small size of these tips can also create problems of DNA shearing. Sample retention due to leaky pipettors or irregular plastic molding (flash) can also interfere with the accuracy and repeatability of pipetting by leaving hang-up volume within the pipette tip that is not completely expunged during the downstroke. Companies such as Rainin regularly bisect their tips looking for plastic burrs or inconsistencies that are the telltale signs of an imperfect or defective mold. However, there are certain techniques the researcher can use to avoid sample retention such as prewetting, which coats the inner wall of the tip. Many companies are now producing pipette tips with thin wall diameters and beveled tips in order to reduce capillary liquid retention. During the injection molding process, additives may be combined with the virgin polypropylene material to give it special qualities that make it either more transparent or easier to cut. With low-retention pipette tips, a light blend of silicon is molded into the plastic, providing a slick surface so that reagents do not adhere to the interior walls. In addition, releasing fluids may be added so that the finished pipette tips don't stick to the molds once they have been cast. This, however, can create special problems. The otherwise inert polypropylene can exhibit characteristics, such as the inhibition of PCR, that is confounding to researchers once the plastic has been adulterated. Because these processes are proprietary, many times researchers don't know that the tips they are using have been subjected to these manufacturing techniques. Although most manufacturers have taken steps to ensure that pipette tips do not have residues that interfere with the pH or the ionic concentration of solutions, occasionally such contaminants do find their way into experiments. One of the latest techniques that has been adopted by companies such as Axygen Scientific is to diamond- polish each of its molds so that releasing fluids are unnecessary. Axygen also has a new nonsiliconized, low-retention tip that makes use of an entirely new polymer technology. However, scientists should be aware that not all tips are manufactured alike and that different brands may yield different results, depending upon how they have been produced. Labcon has stopped making colored tips altogether and now uses a medical-grade polypropylene that is rated by the FDA for use in medical implants. Once the sterile pipette tip has been fastened to the pipettor, the problem of keeping reagents contained within the tip may further complicate matters. Many pipettors are equipped with filters or blowout features that purge the instrument of contaminants. They can also be disassembled and, in many cases, autoclaved to ensure cleanliness. However, taking pipettors apart and putting them back together after every use can be a laborious and time-consuming process. Dave White perfected the self-sealing filter as a solution to the task of repeated cleaning while he was at Molecular BioProducts. He later introduced a micropore hydrophobic filter, constructed of polypropylene, that kept liquid from being drawn into the pipettor. Although cellulose acetate filters have been substituted for polypropylene in some filter tips, these tend to absorb whole samples in addition to the overflow they are intended to protect against. Many companies now offer their own brands of filter tips. Mark Brolaski, lab director of Mo Bio Laboratories Inc., San Diego, Calif., has been testing and certifying pipette tips for over five years. Brolaski agreed to be interviewed in order to dispel some of the myths and correct some of the general misconceptions about pipette tips. One of the most pervasive, and certainly the most inaccurate, of these beliefs is that all tips undergo the same basic inspection process and have the same level of quality. Not so, says Brolaski, who has witnessed a broad range of quality and performance. Brolaski has seen contamination in products that are not regularly tested for DNA, DNAse, RNase, and endotoxins and believes that these products are making their way into laboratories. The way to avoid this problem is to use pipette tips that are certified by an independent testing laboratory such as Mo Bio Labs. Rainin, Molecular BioProducts, Axygen, and Point Plastics have their tips routinely tested by independent labs, and according to Brolaski, "Their tips ensure better quality." Although the large-scale manufacture of pipette tips has become streamlined by robotics, human contact is still a requirement in injection molding. By employing precautionary measures at varying levels of stringency and sophistication, manufacturers have reduced opportunities for contamination. These practices may range from open environment facilities to Class 10,000 clean rooms. The heterogeneity of the industry combined with its secretive nature precludes a standardized set of manufacturing codes. Once again, the only assurance of uniform quality is independent verification. Finally, there has been some dispute as to whether chemical sterilization or gamma irradiation is superior for treating pipette tips. Some argue that chemical sterilization is inferior to irradiation because it is a hands- on process. However, Brolaski insists that gamma irradiation does not remove RNase or endotoxins, and it damages but does not remove DNA contamination. BrandTech's submicro Transferpette Pipetting involves an economy of size, precision, and repeatability. These few constraints have, remarkably, produced a category of instruments that have been so precisely engineered to fulfill a specific function that performance and appearance have evolved into a well-defined archetype that is immediately recognizable. So close do these instruments operate within a given range of tolerances that even minor variations in performance or materials is cause for great interest. When a new pipettor is introduced it accomplishes one of two things. It either confirms the standard design by streamlining accepted conventions, or it emphasizes a specific mechanism for achieving some specialized adaptation. The new pipettors for 1999 can be classed into one of two categories: those that confirm the rule and those that capitalize on an exaggerated adaptation. Multichannel pipettors and submicros, as well as every pipettor mentioned in this article, fall into the latter category. They are the duck-billed platypuses of pipetting. Cut off from familiar territory and exposed to strange new environments and demanding new applications, they have broken off from the main line of pipettors. From the company that makes pipettors for some of the biggest names in pipetting comes a new Single-Channel Electronic pipette. This instrument provides pipetting, dilution, dispensing, multiple dispensing, sequential dispensing, multiaspiration, and mixing in 25 different speed settings. The new submicro Transferpette® pipette by BRAND pipettes small volumes from 0.1 to 1.0 µl in the vanishingly small increments of 0.005 µl. In these small volumes, the compressibilty of the air column in a typical air-displacement pipette is a major source of inaccuracy. The submicro Transferpette pipette, in conjunction with BRAND's exclusive nano-cap™ tips, drastically reduces the column of air between the piston and sample. Accuracy at nominal volume is 2 percent, or 0.02 µl, with precision at 1.2 percent, or 0.012 µl. The ultrathin bore and walls of the nano-cap tips allow visual confirmation of sample volume and precise sample placement. BrandTech also has a unique high-volume Positive Displacement Transferpettor™ developed for difficult media. Often, when trying to pipette viscous media such as glycerin, fats, oils, or cosmetics, the high resistance of these materials causes the air column in typical pipettors to expand, changing the calibration of the instrument. In the Transferpettor the piston directly contacts the sample, eliminating the air column and, consequently, the opportunity for variation in the sample volume. This instrument is ideal for use with high-vapor-pressure media, foaming media such as tenside solutions, and even such high-density media as mercury and sulfuric acid. Brinkmann's new Eppendorf® Repeater® Pro pipette is being heralded as the first electronically operated repetitive manual dispenser. Microprocessor control provides reproducible results and ensures fatigue-free operation in a wide volume range from 1µl to 50 µl. The pipettor can be set for timed dispensing with preset time intervals between 0.1 and 1.0 second. As many as 100 dispensings can be completed using a single Eppendorf Combitip® Plus Tip. The Repeater Pro pipette also employs an automatic tip recognition system that recognizes Eppendorf Combitips and displays the mode and the number of dispensing steps. Small increments allow hundred of volume selections. The Volac Ultra is the only United Kingdom-manufactured digital pipettor. Designed for export to the Far East and Latin America, the Ultra was intended to be an easy-to-use, go-anywhere pipettor that requires little or no maintenance. In fact, the PTFE seals can be installed in 5 to 6 minutes, and a special calibration tool allows the volume to be changed with a simple turn of a screw. Greenfield also provides detailed diagrams and wall charts for recalibrating all makes of pipettors. Hamilton is offering an entirely new line of pipettors with its SoftGrip™ Pipettes. The SoftGrip pipettes include adjustable volume, fixed volume, multichannel, and positive displacement models. Each of these instruments is autoclavable and features a soft nonslip handle that is designed to fit the user's hand comfortably. A sloped plunger button is designed with a short stroke and low spring tension to reduce fatigue. Pipetting of volumes from 0.2 µl to 1,000 µl are attainable with these instruments. Jencons has two new specialty units for 1999: a Reagent Dispensing Pipettor for microliter volumes of 100-5,000 µl, and a microvolume Electronic Sealpette with a crystal microtip. Both of these instruments are designed with the purpose of reducing "dead-volume" in the tip, making them suitable for PCR, sequencing, and other bio- technology applications. Labsystems has developed what are essentially two bookends to the pipetting industry. Its new Pen Dispenser is a very simple and easy-to-use manual repeating pipettor that is small enough to fit in one's shirt pocket. The Finnpipette® 384, by contrast, is Goliath compared to the Pen Dispenser's Davidian frame. Bristling with an array of 16 pipette tips, this pipettor is the first of its kind. Designed for high-throughput applications, the Finnpipette 384 hand pipettes into 384 well plates, and is the dynamic component of Labsystems' Advanced 384 technology. The Impact Equalizer™ from Matrix Technologies is one of those deceptively simple inventions that has other manufacturers kicking themselves for not having thought of it first. A push/pull rod allows the user to spread the tips to accommodate a variety of well plates from 9 mm microplates to 14.15 mm 48-well plates. The remote location of the spreader also reduces the possibility of sample contamination. Currently, Impact pipettors are the only electronic pipettors with an FDA clearance. Mettler-Toledo has been innovative in standardizing the components of its LiquiSystems pipettors. Much like the revolution in weapons manufacturing that was ushered in by Rueger's first rifle with interchangeable parts, this could prove to be an important step forward in systematizing the production of pipettes. Mettler-Toledo's ValuMate and MultiMate pipettors include an assortment of ten instruments for volume sizes from 0.1 to 5,000 µl. Tips from all leading manufacturers can be used with these instruments. The AlphaPette™ is Molecular Technologies' entry into the pipetting market. This bright red pipettor is a standout in the usually dismal world of gray and black that comprises labware in general. Although similar in design to Rainin's pipettors, the AlphaPette typically is about 20-30 percent cheaper. The AlphaPette is equipped with a µlPLUS direct-drive digital volume readout submicrometer for greater accuracy and also has two different-size ejector buttons for small and large fingers. It also comes with an 18-month warranty and a coupon for a free calibration. Labnet's Labpette 2.0 µl Ultramicro Digital Pipettes are continuously adjustable high-precision instruments that cover a range from 0.5 to 5,000 µl with six different models to choose from. Self-lubricating, self-adjusting seals as well as a stainless steel piston provide corrosion protection, while a digital micrometer and recessed volume-adjustment thumb wheel ensure the accuracy and repeatability of dispensing. An optional rotating carousel rack or linear pipette stand is available for storing these instruments out of harm's way. Nichiryo's new Nichipet-EX UV-resistant autoclavable digital pipette allows prolonged exposure under UV light. Smooth plunger action and a thermally insulated handle keeps heat from causing measurement errors after repeated use. It is also lightweight. An enlarged finger-rest reduces operator fatigue, and a dial lock prevents accidental volume changes. Optional parts for organic solvents are also available. The Oxford Benchmate Multi-8™ and Multi-12™ continuously adjustable multichannel pipettes include four different models. Each is equipped with a locking mechanism that prevents accidental volume changes, thermally insulated handles that keep body heat from affecting measurements, and maintenance-free O-rings designed to minimize dead air space. Oxford's customers are also assisted by a dedicated technical support group that specializes in troubleshooting the specific needs of Benchmate owners. Oxford's next line of pipettors, which will be making its debut in May 1999, is reported to have such features as autoclavable, UV-stable materials and a simpler maintenance protocol. New from Rainin is its LiteTouch™ tip ejection system, which is engineered to eliminate repetitive strain injuries. Because tip ejection is the highest singular force exacted during pipetting, Rainin has introduced a new fitting between the shaft and the pipette tip that reduces the net force that must be exerted in releasing pipette tips. The traditional conical and thick-walled tip has been replaced by a cylindrical shaft with a thin-walled tip. The LiteTouch system is also assisted by a positive-stop shelf that lets the user know when the seal has been made. The result is an ejection force that requires only 500-600 grams of pressure. The LiteTouch system is available in each of Rainin's new pipettors: the EDP3™, the Pipet Plus®, and the Pipet-Lite™, which has a magnetic assist feature. World Precision Instruments' Spectropipettor Similar in kind to Drummond's positive displacement pipette, the Spectropettor from WPI permits spectroscopic analysis while pipetting microliter volumes. The pipettor itself is a stainless steel tube with two optical fibers that transmit light reflected from the alloy mirror at the tip of the instrument to the spectrometer at its base. This technology was made possible by Teflon ES, which was patented at the end of 1989. The low refractive index of this material traps light inside the core, making quick and accurate measurements possible. WPI also has five new adjustable pipettors that are UV resistant and autoclavable. These pipettors may be user calibrated and have in-line micrometers for rapid volume changes. They are some of most competitively priced pipettors currently available. Wheaton Scientific's new Calibra® Digital 8-Channel Micropipette is the fifth digital multichannel pipettor to be added to the Calibra line of pipettors. This instrument, which pipettes submicroliter volumes up to 10 µl, provides a rotating handpiece and simultaneous tip ejection. It also includes Calibra's unique stepped cam system, which uses permanently calibrated fixed stops for each incremental volume setting. Table of Specialty Pipettors Table of Specialty Pipette Tips The author, Brent Johnson, can be contacted at bjohnson@the-scientist.com.

Special Delivery: New and exotic products for specialized pipetting

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