MULTIPLE OPTIONS FOR MANUAL FLUID SAMPLE DELIVERY
Pipettes are familiar to any lab worker who needs to transfer small quantities of liquid. Research and development labs in the chemicals, foods, materials, and paints industries use pipettes routinely, but the life sciences arguably consume the largest volume of pipettes and related supplies.
Pipettes come in many varieties, and most feature plastic disposable tips. Note that syringes serve many of the functions of pipettes but tend to be less accurate. Syringes typically are used in situations where the liquid must be delivered to a closed or sealed system, such as a reaction vessel or chromatograph.
While pipettes are handheld, their delivery mechanism may be manual or electronic. Manual delivery refers to the operator’s thumb depressing or releasing a piston to deliver or withdraw liquid. Electronic pipettes still require the user to activate withdrawal and dispensing, but the work is done by an electric motor.
Pipettes are sold in two basic formats: fixed volume, which always dispenses the same quantity of fluid, and adjustable volume, which delivers a range of volumes. Adjustable pipettes are accurate from about 10 percent up to 100 percent of the volume range. Single-channel pipettes use one tip at a time, whereas multichannel devices hold multiple tips for simultaneously delivering fluids to multiple locations. Biologists who work with microtiter plates, immunoassays or polymerase chain reaction probably will be interested in multichannel pipettes.
“The big advantage of electronic pipettes is ergonomics,” says Jason March, marketing director at Hamilton (Reno, Nev.). “They also allow you to do more; for example, filling the tip once and dispensing multiple times.” Those researchers who use pipettes occasionally or who switch volumes often probably are better off with a manual pipette, he advises.
Ergonomics is a huge issue in pipetting. Most vendors, including Hamilton, Mettler Toledo (Columbus, Ohio), VistaLab (Mt. Kisco, N.Y.), Cole-Parmer (Vernon Hills, Ill.), and BrandTech Scientific (Essex, Conn.), manufacture ergonomic pipettes. “There’s no denying that excessive repetitive motion can be bad for you, be it in pipetting, typing or other tasks,” notes Akbar Anwari, marketing manager at BrandTech.
Pipette manufacturers have tried to minimize the forces used in single-channel pipettes in a number of ways, as Mr. Anwari explained.
Reduction of static strain by reducing the pipette’s weight and redesigning the device so it drapes over the operator’s hand instead of being held are two fixes. BrandTech has achieved these through its Transferpette pipette line, for example.
Another technique is to reduce the force required to draw liquids. Most pipettes use “softer” springs or a shorter stroke length to reduce these forces. Anwari claims that the Transferpette line “harnesses the power of the muscles used to move the thumb.”
Tip ejection forces tend to be the largest forces used on pipettes, especially multichannel pipettes, where tips are ejected eight or 12 at a time. Ergonomic strategies based on lessening these forces reduce the spring tension or involve redesigns that minimize contact between the tip and the tip cone. “But if there’s too little contact, the tip either will not seal properly or will not sit straight on the tip cone.” Manufacturers have attempted to solve this problem by introducing O-rings or V-rings to reduce the forces required to obtain a good seal but that allow the tip to be ejected more easily. Another innovation for multichannel pipettes involves ejecting tips two at a time rather than eight or 12 at a time.
Mr. Anwari also believes that non–ergonomic design features can make pipettes easier to use. For example, positioning the display so it is not covered by the hand during use reduces the need to shift the instrument to verify volume settings. Another feature is the ability to adjust the volume with one hand without shifting the device.
Accuracy and precision are the two major factors that play into pipette purchases, says Mark Dostalek, marketing communications manager for Gilson (Middleton, Wis.). “Customers have to know that they’re aliquoting the right volume.” Like other laboratory devices, pipettes must be calibrated and validated for the type of work they do, particularly in regulated industries. Pharmaceutical and biotech work, for example, is done under Good Laboratory Practices (GLP), which is a regulatory designation. Many end users today choose motorized electronic pipettes for GLP work. The devices record volumes and number of cycles and even can provide out-of-specification warnings.
“Plus, once you introduce a motor, you can do things like mixing within the tip, reverse-pipetting, and interfacing with a computer to track data and calibration intervals and perform advanced maintenance.”
Angelo DePalma holds a Ph.D. in organic chemistry and has worked in the pharmaceutical industry. A full-time freelance writer for more than 20 years, Angelo has written nearly 2,000 trade-magazine articles on pharmaceuticals, biotechnology, materials and supporting industries. You can reach him at firstname.lastname@example.org.