Support

Discussion and Proposal on Management Methods for Micropipettes
Naoto Izumo
R&D Division 5, A&D Company, Limited

In the more than 100 years since Louis Pasteur's breakthroughs establishing the field of microbiology, Western medicine has advanced remarkably to its present sophisticated levels. With its origins in the glass pipette, the micropipette, capable of measuring minute amounts of liquids to a high degree of precision, has been one of the essential tools in supporting these achievements, as a requisite piece of equipment in a biotechnology lab.

Presently, over 100,000 micropipettes are sold in Japan every year, and worldwide sales amount to over a million. Major pharmaceutical firms will often have several thousand micropipettes at just one of their main research laboratories. Micropipettes' two most valuable characteristics are their ability to dispense tiny amounts of liquids, together with the easy handling provided by disposable pipette tips, which retain the sample being measured via air pressure, providing a reduction in occurrences of pipette contamination and also of the laborious process of cleaning pipettes. As a result, it could be said that micropipettes have made a significant contribution to improving the quality and productivity of testing and inspecting processes and are an indispensable tool in many aspects of biotechnology, pharmaceutical, foodstuff and clinical research.

While this convenience of use has meant the micropipette has come to be used in a wide variety of situations around the world, it would be hard to say there is a firmly established method for micropipette management. One of the reasons for this is the lack of an established method for managing its volumes as a quantity-measuring device. For example, while pipettes can determine volume, they are different from weighing machines in that they do not use weights or equivalent which can act as a reference standard for managing volume. This could be considered a very serious problem. Presently in pipette makers' reports of results, volume (V) is determined from a calculation of V = m ÷ρ, where the coefficient of ρ is the density of purified water, which is a known quantity, and mass (m) is found by dispensing the purified water with a pipette on the tray of a balance and reading the displayed amount. However, the density of the water will change according to its temperature, so it is necessary to perform density correction at each different temperature. Another problem that could arise in practice is the pipette user dispensing a liquid other than water, with a different density. Further, the viscosity of water at 20°C of 1.002 mPa?s is extremely small and even a water solution with 50% glycerol will result in a viscosity level several times higher than purified water. Therefore, even if the pipette is calibrated with water, the density and viscosity of the liquid that is actually dispensed could differ from calibrated water and the interchangeability of the volumes will not be ensured, due to differences in the viscous resistance.

With micropipettes, the differences in air pressure created by the movement of the built-in piston are used for aspirating and dispensing of the liquid. Therefore, even with the same volume settings, differences in volumes will occur not only due to the viscosity and density of the liquid, but also the shape and material used for the tip. It is probably quite clear then, that with these conditions influencing measurement, dispensing volumes which differ from the pipette's report of results is a quite a concern in many cases.

Besides such technical problems, there are also problems connected to the method of use of the pipette user. Namely, there are often individual differences in the manner of operation between users, as the pipette is held in the hand all day and it is also a very small tool to handle. Further, when the pipette is dropped from a desk or the hand, these kinds of impact loads can cause deformations in the operating rod or damage to the structure, which is associated with a reduction in precision in dispensed volumes.

With considerations such as these ones above, I started to have doubts about current pipette management techniques and thought about what kind of management methods should be used for pipettes under normal circumstances. For example, while you could say that having the pipette maker issue a calibration report once or twice a year is an important management technique, it is unrealistic to confidently assert that traceability or validation can be ensured in between periodic inspections that only occur once or twice a year. Further, even if calibration is performed with purified water and the tip specified by the manufacturer, there are other variations that can occur at the place of use other than the constitution of the liquid or the type of tip used, such as influences of the measurement environment or the degree of expertise of the user. I could only come to the conclusion that it is difficult to ensure traceability in the place of measurement with just the pipette maker's report of results used for reference. Next, considering a solution to these problems, I was able to put my many years of experience in development of weighing devices to work by summarizing my proposed measures into the following two points:

1. As a precision weighing device manufacturer, we have a duty to provide to the market a management tool which can allow daily and periodic checks of pipettes at their place of use.

2. A new pipette is needed which allows pipette calibration management that reflects the actual conditions it is used under.

These two points above would be satisfied by providing, for example, devices that allow testing the pipette at the place of use when any kind of trouble eventuates, such as dropping it or aspirating too much liquid; a pipette equipped with a calibration function that applies the tip and liquid used, making it easy to perform calibration that actually fits the conditions at the place of use; and measures by which pipette maintenance can be performed easily by the user themselves.

As a result of the considerations mentioned above, in April this year A&D became the first manufacturer in Japan to release a general-use electronic pipette. Preceding this, we also developed a pipette leak tester and accuracy (volume) tester for pipette users five years ago. Using these management tools, it has become possible to create standard operating procedures (SOP) for pipette management to be carried out by users themselves. Further, we have also recently developed the AD-1695 dedicated pipette management tool which does not require the use of a PC. As the AD-1695 allows interactive operation with its graphic user interface, daily and periodic checks of the pipette can be performed with ease at user level.

Our newly released original electronic pipette is equipped with calibration functionality in μl units and allows volume calibration by users themselves. For calibration in μl units with liquids other than water, difficult density measurement of the liquid is required. To help with this, we have also added a new calibration and display function with mg values. By performing measurement and calibration of volume with mg units, measurement and correction of density is no longer required and pipette calibration can then be performed using the mg value displayed by the balance. Having a uniform unit of mg for measurement and calibration means calibration with the liquid and tip to be actually used becomes much easier to perform, and means that a mixture consisting of a measured amount of powder and liquid can be simply and accurately calculated by weight ratio.

With the MPA series of electronic pipettes, the lower part of the device including the piston, which is often subject to contamination, and the main part of the pipette (control and drive parts) are designed as separate units, so can be easily detached from each other. Therefore, sterilization using an autoclave is now possible for the lower part only, and due to the design of the MPA series this part can also be simply disposed of and replaced by anyone when contamination or wear occurs.

As a result of our considerations over the last five years, I think that we have finally achieved a range of nearly ideal micropipettes and accompanying management tools that offer practical solutions for the actual conditions that are encountered in everyday pipette use. I hope that these devices can be used both as an aid to creating SOPs for those responsible for pipette management and also as effective tools for ensuring safe and reassuring use for pipette users. A&D has already prepared original guidelines and documents on these subjects that enable simple creation of SOPs for pipette management. Please feel free to contact us at any time to discuss any matters relating to our pipettes and pipette management tools.

<< Return