Pipetting using Mechanical pipettors
By Cathy Tugmon 2008
Introduction
Throughout the semester you will need to use mechanical pipettors to accurately
measure small volumes of liquids. Therefore, it is very important that you spend
sometime practicing with them to be able to continually dispense a consistent and
accurate volume. It would be a good idea to go to
http://www.aug.edu/biology/biol1107PrinciplesofbiologyI.htm
and click on “pipetting helps” to watch a video on how to pipet before coming to lab.
Methods
Today you will working with 3 different pipettors. They are differentiated by the
volume of liquid they can accurately pipet.
Table 1: Mechanical Pipettors
The information contained here is to help you know which
pipett to use for which volume. CAUTION: Never set a pipet
above or below its indicated range or you will break it!!!!
Name of Pipettor
Range of liquid dispensed
P-20
2-20 µl
P-200
20-200 µl
P-1000
100-1000 µl
Today in lab the instructor will show you how to set each pipetman to the correct
volume. They will also demonstrate the 2 stops on the pipetmen. Remember that the 1st
stop is only used to draw the correct volume into the tip placed on the pipetman. The 2nd
stop is only used to dispense the entire volume from the pipet tip. The instructor will also
show you how to put pipet tips on and how to eject pipet tips.
It is critical to your success in future labs to take the time to practice with each
pipettor. Watching you lab partner will not allow you to develop the necessary skill –
this is a learned behavior.
After paying close attention to the demo and explanation by the lab instructor,
you will practice by completing the following Table. It is important to note that 1 g of
water is equal to 1 ml of water and that 1 mg of water is equal to 1µl of water. Using this
information you can pipet the volumes of water listed in the table into a cup on a balance
and determine by weight if you have pipetted the correct volume. For example, if I draw
up 860 µl of water then when I pipet it into the cup on the balance (after I have zeroed the
balance) I should see 0.860 g on my balance. If I see some other reading it indicates that
I need to practice more until I pipette the correct volume.
Each member of the lab group needs to take turns to complete the following table. You
may want first to practice drawing in liquid and dispensing it. Once you have the
technique down pick up a pipet and pipet the volume indicated the table that goes with
that pipet. There are two volumes to be obtained with each pipet.
Table 2: Practicing Pipetting
Set the appropriate pipet for each of the volumes listed in the first column. Pipet each
volume 2 times or until you get an accurate weight. Record your best 2 attempts.
Volume
Weight
Weight
1000 µl
513 µl
50 µl
156 µl
*2 µl
*17 µl
*These volumes require a more sensitive balance and will only be done if that balance is
available in lab or if we have some pre-marked tips for these amounts.