| which size? | reading the volume | setting volume | basic technique and grip | small volumes | check calibration |
A. Gilson-style
Pipetmen Micropipets (and similar models)
We primarily use the Gilson micropipets in the core course labs. We have four sizes identified by the number on the round button on the plunger. The value is the maximum volume in microliters that can be transferred with that size pipet.
|
Size indicator button on a Gilson P1000. |
Other autopipet sizes we have on hand.
|
What size of micropipet is right for the job?
RULE OF THUMB: Always select the SMALLEST size pipet that will handle the volume you wish to move to achieve the greatest accuracy. Accuracy decreases as you use unnecessarily large pipets for small volumes.
The following table shows the useful volume ranges for each pipet type. Make special note of the min and max values.
SIZE
Useful Range
Max Volume
Min Volume Gilson-style P1000;
Finnpipette 100-1000 ul~200-1000 ul 1000 ul 200 ul Gilson-style P200;
Finnpipette II 20 -200 ul20-200 ul 200 ul 20 ul Gilson-style P100 10-100 ul 100 ul 10 ul Gilson-style P20;
Finnpipette II 2 -20 ul~0.5-20 ul;
2 - 20 ul20 ul 0.5 ul; 2 ul
B. How to Read the Volume on the Micropipet
Look at the front face of the pipet and you will see a window with 3 (three) digits inside. The diagram below shows the MAXIMUM value that can or should be dialed in on each size pipet. To exceed these values will put the pipet out of calibration. Beside each "window" below is the numbers place it represents. Please take the time to learn how to read them so as to avoid damaging them by dialing values out of their range.
Note that some of the smaller volume models have one or two decimal places.
Gilson-style P1000 scale window.
P1000
P200,P100
P20
1 1000's
100's
10's
2,1 100's
10's
1's
2 10's
1's
1 decimal
0
0
0
0
0
0
C. How to change the load volume:
Hold the pipetor horizontally with the plunger to your left. Change or set the load volume by turning the knurled plastic knob at the top of the hand grip. Roll it towards you to decrease the values and away from you to increase. WATCH CAREFULLY as you change the values to make sure you dont take the numbers out of range. If in doubt, review the allowable volumes for each size pipetor, and then ask for help.
D. Technique
- GRIP: There are two typical ways that people hold micropipets: the index finger grip, and the thumb grip (see figure below). Hold the pipetor like a knife in a horror flick with your index finger OR thumb on the plunger. While it's a matter of personal preference, some argue that your index finger gives you much finer control over the plunger action. As seen in the photos below, however, some micropipets are clearly designed for the thumb grip.
Index finger grip Thumb grip
- LOADING: Load a sterile tip (blue for 1000 ul pipettes; yellow for P200 and all smaller sizes including) and then reclose the tip box to maintain sterilitiy.
- Push the plunger down slowly to the point of first resistance: this is the load volume.
- While holding the plunger at the load volume set point, put the tip into the solution so that it is immersed just enough to cover the end (3-4 mm).
- Slowly release the plunger to draw up the liquid making sure to keep the tip immersed. Visually inspect the load to make sure it is correct - there should be no air space in the distal end tip.
- Performance may be improved by prewetting the tip once or twice (load and discharge a small amount) before actually loading for delivery.
- DELIVERY: To deliver the volume, place the tip into the receiving vessel and press the plunger all the way to the bottom - this expells all the liquid and gives a little extra volume to get the last droplet out - AND THEN, WITHOUT RELEASING THE PLUNGER, withdraw the tip.
- CHANGE TIP? Repeat as necessary using the same tip if NOT changing solutions/cultures. Use a fresh tip for every change of solution, or whenever it is prudent to maintain sterile conditions and avoid cross contamination of solutions or cultures.
- TIP DISCHARGE: While holding the tip over an appropriate waste receptacle, press the white tip discharge slider on the back of the grip.
E. Small Volumes Technique: With small volumes, especially the 1-10 ul range used in molecular biology protocols, you must keep track of the droplets you pipet. Carefully expell the liquid droplet on the side wall of the tube so that you can see it, drawing the tip away/out carefully BEFORE releasing the plunger.
If adding to a larger volume, flush the tip with the solvent liquid after expelling the droplet to make sure you get all the delivery liquid. With small volumes you'll usually need to centrifuge and then vortex the tube to get a good mixing of the reagents.
F. A Simple Check for Proper Calibration
Check the calibration of your micropipet by using the fact that 1 ml of deionized (or distilled) water has a mass of 1 g. Pipet a range of volumes spanning the micropipet's usuable range and mass them on a top loading balance having at least 3 decimal place accuracy. Pipets having greater than 5 % error should be recalibrated.
Modified 9-29-08 gja
Department of Biology, Bates College, Lewiston, ME 04240