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Development of Devices for Pipettes
(Pipette accuracy tester: AD-4212B-PT / Leak tester: AD-1690)
Naoto Izumo
R&D Division 5, A&D Company, Limited

A&D now offers pipette accuracy testers and leak tester for pipette inspection.

For the development of the series of pipette accuracy testers, we considered pipette calibration business prevalent in Europe, and adopted the gravimetric method, which uses a balance for volume verification. The leak tester and the pipette accuracy testers offer a new way to routinely manage pipettes on-site through leak tests and dispensed volume measurements. In particular, the leak tester AD-1690 is the world’s first product that easily detects leakage in a pipette including the area around its piston and enables the user to judge quickly whether the pipette can be used or not. Although the functions of the AD-1690 are rather simple, we are confident that the product goes a long way in relieving the accuracy concerns of users.

A&D has been developing electronic balances since its establishment more than 30 years ago. By leveraging our balance technology, we have also made efforts to cover more types of physical quantity measurements. For example, we have released such products as moisture analyzers and viscometers to measure moisture rates and viscosities of substances. This time, our focus was on the development of a device with a new function, the measurement of volume dispensed from pipettes. In order to obtain volume from mass, it is necessary to know the density of the measured liquid beforehand. Distilled water is generally used to determine pipette volume since its physical properties are well defined. The conversion factor from mass to volume is called the “Z factor.”

Our developmental challenges revolved around three points. First was the calculation of the Z factor. Second, a balance readability of 1 μg (1 nL) was required. This was necessary because high precision pipettes (called micropipettes) at their smallest have a nominal volume of 2 μL, which requires a display readability of 1 nL (1 μg) for accuracy verification. Finally, a means was necessary to minimize water evaporation during the volume measurement without compromising operability.

The second point was especially difficult and took time to resolve. For one thing, A&D had never produced a balance with a display readability of 1 μg. Furthermore, the balance had to be small and portable so that accuracy verification could be performed at the different locations pipettes are actually used. We solved these problems by adding another decimal place to the existing AD-4212B, which was a production line balance with a readability of 10 μg.

For an ordinary balance, linearity is required for its entire weighing range and a stable weighing result has to be displayed for a certain period. However, quick weighing with a high sensitivity equivalent to a mass comparator is preferred when weighing minute volumes. We developed special software that calculates the Z factor, detects the stable mark display of the balance, and imports the weighing data automatically. Using this software, we achieved measurements of 1 μg (1 nL) with high stability and repeatability. Moreover, we also developed our unique evaporation trap, which, while allowing easy access for the tip of the pipette, passively controls the evaporation of the test liquid inside. The evaporation trap was made a standard attachment for the pipette accuracy tester to reduce the measurement uncertainty.

Technologies for minute volume measurements have yet to take root in the market. We hope that our leak tester and the accuracy testers will be used for the daily, on-site management of pipettes to help provide compliance with ISO regulations, GLP, and SOP, and enhance the quality and productivity of research.

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