A Novel Mechanism for Controlling and Monitoring Real-Time Pipet Information in a Manual System

The modern manual pipet has been a laboratory workhorse for several decades, providing researchers with a convenient tool to transfer liquids from one vessel to another with high levels of confidence in the reproducible precision of the associated volume. Development of the fundamental technology has included an expansion of the available volume to cover sample volume ranges from 0.1 μL to 20 mL; in parallel there has been the introduction of multichannel versions for higher-throughput requirements. During the technology development process, it was recognized that pipetting had become such a well-used laboratory tool that continuous use of the manual pipet was likely to place a strain on the muscles, tendons, and ligaments of the hands and wrists of each researcher. In fact, many researchers literally suffered for their work.

Ergonomics and pipets

Enter the era of ergonomic pipet development, a period of designing the pipet to enable the researcher hours of use without the risk of repetitive strain injury (RSI). All parts of the pipet were assessed for their contribution to the loads associated with RSI, including tip-ejection forces and plunger forces associated with the various steps involved in pipetting. Careful design of the plunger/springs and micrometer were critical to maintaining precision and reducing forces associated with the aspirate, dispense, and blow-out steps. Alternative mechanisms for moving the plunger and piston were developed for the first electronic pipet, removing any requirement for manually pushing a plunger. Researchers could now choose between a manual pipet and an electronic system that could be programmed to automatically perform multiple pipetting steps.

Manual pipets have continued to be popular systems of choice due to their lower cost and the ultimate control that the user has in choosing how to manually push the plunger down. Manual systems, however, lack any form of feedback in terms of exactly where the plunger is positioned and hence the actual volume being aspirated or dispensed.

Advancing manual pipets

Figure 1 - E-Man Hybrid Pipet.

The E-Man Hybrid Pipet (Figure 1) (Rainin Instrument, LLC, Oakland, CA) represents an important step in manual pipet development in that it retains the control and feel of a traditional, ergonomic manual pipet with the additional advantage of being able to determine the exact position of the plunger and display this to the user. This technology (real-time position sensing) enables an LCD to display, in real time, the volume that is being aspirated or dispensed by the pipet.

Real-time position sensing is a well-known technology associated with many industrial systems. Common industrial applications include control systems, robotics, machine tools, and measurement equipment. Besides industrial applications, position sensing is often used in automotive steering, braking, and throttle systems.

In many laboratories, equipment position sensing can often be found in pump systems and in the positioning mechanisms of larger liquid handling robot systems.

In the E-Man Hybrid Pipet, the real-time positioning sensor is used to monitor the precise position of the piston, and therefore the plunger. The position of the plunger/piston, which relates directly to an associated liquid volume, can be displayed directly on the LCD. Current manual pipets with electronic readouts only monitor the position of the upper stop but cannot tell the user where the plunger (or piston) is positioned.

This real-time sensing of the piston/plunger in the E-Man Hybrid gives rise to a number of features that currently have been unavailable in manual pipets.

  • The pipet can display the amount of liquid being aspirated into the pipet tip, or it can display the amount of liquid being dispelled from the tip. For the first time, the user of a manual pipet can perform tasks such as titrating, diluting, multidispensing, and measuring an unknown amount of liquid.
  • The E-Man Hybrid can determine whether acceptable pipet technique is being used by sensing whether a sample has been blown out correctly or if plunger movement is too rapid. This can be very beneficial for teaching new users.
  • With electronic memory, the pipet can alert the user to when the next scheduled service is due, providing a unique GLP function in a manual pipet.
  • The real-time sensing in the pipet allows multiple offsets to be placed into the calibration curve (like Rainin E1 and E3 electronic pipets) as opposed to a single offset in standard manual pipets. This optimizes the performance of the pipet.
  • The user calibration feature also allows correction at more than a single point; up to 50 points can be entered.
  • The real-time sensing in the pipet permits a real pipet cycle counter to be used. The cycle counter does not simply count plunger depressions, but only counts a pipetting cycle if it is a complete pipet cycle; mixing, etc., will not cause false cycles.

The E-Man Hybrid, by employing novel technology within a familiar ergonomic manual pipet, brings new capabilities for today’s scientists that will set the standard for tomorrow’s research.

Mr. Petrek is CTO, Rainin Instrument, LLC, 7500 Edgewater Dr., P.O. Box 2160, Oakland, CA 94621-0060, U.S.A.; tel: 510-564-1600; fax: 510-564-1617; e-mail: pipets@rainin.com.

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