A Low-Cost Pipet Aid PimpKay Hon The Chinese University of Hong Kong, Shatin, N.T., Hong Kong A variety of pipet fillers are available for chemical laboratories. The simplest one is of the rubber-bulb type, which has the drawbacks of not being very easy to control, malfunctioning in the valves, and fatigue in the rubber. The more sophisticated ones are relatively expensive for undergraduate teaching. We recently found a plastic desoldering pump to be a very good pipet filler. It is inexpensive (about $3.00 apiece) and very easy to convert for pipet filling purposes by simply removing the springs and adding rubber tubing at the tip. The filling can easily be controlled by moving the plunger in an up-and-down action with the thumb (see figure). It can also be converted into a pipet pump or an adjustable autopipet.
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gives good reproducibility and acceptable 'accuracy. For smaller volumes, 0-1 mL, one simply needs to replace the plunger with one of a smaller diameter, 6-mm, and put a suitable glass tubing inside the pump barrel.
~ l p e Pump t A 3-mm-diameter steel ball is used for the suction valve. A 1-mm hole is drilled at the lower portion of the pump barrel. This hole may be covered with a wide rubber hand cut from a balloon or simplv with a piece of plastic film of high clinging film used in the kitchen. properties, e.& t h e This assembly serves very well as an air exit valve. A pipet pump is convenient for filling the larger pipets, e.g., 25- and 50-mL sizes.
the plunger, the desoldering pump becomes an autopipet with an adjustable volume of 0-10 mL. After calibration it
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Journal of Chemical Education
tubing for the 0 - t - m ~autopipet: (6) O-ring. (7) glass tubing. (0) epoxy glue, (9) small bwe glass tubing. (e) in operation.
