John Schollar tests equipment for school biology... sometimes to destruction.

In this issue, John tests inexpensive alternatives to conventional micropipettes.

The products under test are:

Poulten and Graf 'Mini pipet'
LTI 'Graduate' pipette
NCBE 'Microsyringe'
Tricontinent 'Minipet'
Eppendorf 'pen' dispenser
Drummond 'Wiretrol II'
Syringe with calibrated tip (DIY)
Alpha 1 mL 'Pastette'

Most secondary schools would find the price of micropipettes for whole class use prohibitive. Typically a variable-volume device will cost GBP 125, and a fixed volume micropipette at least GBP 50.

Devices capable of measuring microlitre volumes are though, an essential requirement if one is to carry out practical molecular biology. Consequently, much ingenuity has been directed over the last 15 years into finding inexpensive alternatives for school use. Early efforts included devices such a conventional syringe with a wire placed down the needle (1). This was in effect a home-made version of the displacement capillary pipettes that preceeded the micropipette. Others used existing materials in a new way by, for example, fitting a calibrated micropipette tip onto a syringe (2), or by using disposable inoculation loops that held known volumes of liquid (3).

Approaches such as these are still useful and depending upon the circumstances, can be highly efective. Increasingly, however, commercial manufacturers have started to produce inexpensive pipetting devices. Some are intended as single- or limited-use items for diagnostic kits and have found their way into schools; others have been developed specifically for the education market.

There is a tendancy to regard these devices as second-best; the school teachers' poor alternative to 'real' equipment. This is a narrow perspective however (unless one is merely in the business of training people how to use apparatus). In the school laboratory, accuracy may be less important than durability and ease-of-use. Many a science centre has seen costly micropipettes reduced to broken plastic after a few months, or realised that the disappointing results with expensive reagents are caused by pipettes that are too difficult and unfamiliar for most visitors to handle. The motivation that students gain by handling 'the real thing' can quickly evaporate when the results don't match up.

Selecting a microlitre measuring device for school use is therefore not a straightforward task. Accuracy, durability, ease-of-use and the cost of consumable items (such as tips) must all be considered carefully.

This survey of 8 devices covers a broad range from the home-made to the repurposed and the purpose-built.

References

1. Schollar, J. (1990) Pump up the volume NCBE Newsletter (10) 14.

2. Miller, M.B. (1993) DNA technology in schools. A straightforward approach.
BIO/technology Education 4 (1) 15-22.

3. See, for example, bacterial transformation kits, such as Bio-Rad's 'Explorer' series that use disposable inoculation loops for dispensing plasmid DNA.