Training Tips allow students to see what a specific volume of liquid
should look like under these different circumstances.
Training Tips have worked well to train both first-year and
upperclass college students, as well as nontraditional students, to
pipette. Given the obvious visual cues Training Tips provide, they
could also be used to teach high school students and middle school
students. The scope of the exercise, number of replicates, volumes
used, and assessment activities should be modified depending
upon the students receiving instruction.
Viscosity and surface tensions of liquids can severely affect
pipetting. Unfortunately, many such liquids are solvents and/or
leave residue in tips, thus using Training Tips with these liquids
is less efficient, especially in a classroom setting. However, Training
Tips can still be used as a guide by being held next to a tip after
pipetting a more viscous liquid, and will help students gain an
appreciation for how viscosity affects pipetting.
Pipetting accuracy can be assessed in a number of ways and will
depend upon the students and lab infrastructure. To assess middle
school and high school students, visual observation of pipetting
using Training Tips may be appropriate. For more advanced students, accuracy can be assessed in a number of ways. Students can
weigh pipetted water using an analytical balance of sufficient precision and determine how accurately they pipetted. Alternatively, students can make dilutions of a dye of known absorbance and test the
accuracy of the dilutions using a spectrophotometer. Both of these
assessments require additional infrastructure, and instructors should
implement these methodologies as appropriate.
Conclusion
Micropipettes are an essential tool in many fields and learning to use
them is a fundamental part of a scientist’s training. I have developed
Training Tips, a homemade tool to teach pipetting to novice bench
scientists. Training Tips provide obvious visual marks by which one
can monitor pipetting accuracy and are a cheap, convenient tool to
guide micropipette instruction in the classroom and laboratory.
References
Guzman, K. (2001). Pipetting: A practical guide. American Biology Teacher,
63, 128–131
White, H. B., Benore, M. A., Sumter, T. F., Caldwell, B. D., & Bell, E. (2014).
What skills should students of undergraduate biochemistry and
molecular biology programs have upon graduation? Biochemistry
and molecular biology education, 41, 297–301.
Lessard, J. C. (2013). Molecular cloning. Methods in Enzymology, 529, 85–98.
Matsumura, I. (2015). Why Johnny can’t clone: Common pitfalls and not
so common solutions. Bio Techniques, 59(3), iv–xiii.
DOUGLAS A. BERNSTEIN ( dabernstein@bsu.edu) is an Assistant Professor
in the Biology Department in the College of Sciences and Humanities at
Ball State University, Biology Cooper Life Sciences Building, CL 121, Muncie
IN 47306.
APPENDIX
Tips for Accurate Pipetting
Provided below are general tips for accurate pipetting. Depending upon the brand of pipette tip and pipette being used, recommended techniques may vary slightly. Always check with manufacturer for best practices, and check with your instructor
for recommendations on how to handle the pipette.
1. Pipettes have particular ranges of volumes in which they are accurate. For a given volume you should choose a pipette in
which the desired volume falls within the pipette’s range. (The closer to the middle of the range the better. For instance, to
pipette 100 μl, you would use a P200 as opposed to a P1000.)
2. Make sure to press the tip firmly onto the pipette, because a loose tip will not draw the proper volume of liquid.
3. Slowly depress the plunger before submerging the tip into the liquid.
4. Submerge the tip 3 to 4 mm into the liquid. The more you submerge, the more liquid may stick to the outside of the tip.
(Make sure the tip remains submerged as liquid is brought into the pipette.)
5. Slowly release the plunger of the pipette after the tip has been submerged. Slowly releasing the plunger will limit the
amount of air bubbles you draw into the tip.
6. Hold the pipette vertically when moving and dispensing liquid.
7. Hold the tube you are pipetting into at an angle (~45 degrees) and pipette either into the liquid in the tube or onto the
side of the tube.
