The Micropipette

Micropipettes are used for accurately transferring small volumes of liquid in the milliliter and microliter range. We will cover three basic sizes of these handy little instruments.

• The P - 1000 accurately delivers 200 to 1000 microliters.
• The P- 200 accurately delivers 30 to 200 microliters.
• The P-20 accurately delivers 2 to 20 microliters.

The liquid is drawn into, and dispensed from a disposable pipette tip - The disposable tip is changed between liquid transfers. Pre-rinse every new pipette tip with the liquid to be pipetted.

Despite the differences in micropipette shapes and sizes, they have the same basic parts:

• a plunger for drawing up and expelling liquids
• a dial for tuning the pipette to different volumes
• the display, and an ejector for launching tips towards wastebaskets.

The volume is set by turning the dial. When decreasing the volume, slowly turn the dial to reach the required volume. Be careful not to overshoot. When increasing the volume, pass the desired volume by one-third turn and then slowly decrease the volume to the final mark.

The display is read from top to bottom. For a P-1000, the volume is given in milliliters. The top position is the ones place, the middle is the tenths place, and the bottom is the hundredths place. In the P-200, the top position is the hundreds place, the middle is the tens place, and the bottom is the ones place. The top position in the P20 is the tens place, the middle is the ones place, and bottom is the tenths place.

Normal operations consist of the following steps:

Preparation: Hold the instrument in a nearly vertical position. Depress the plunger smoothly to the first stop.
Aspiration: mmerse the pipette tip in the liquid. Allow the plunger to move up smoothly to the rest position. Wait one second so that the liquid has time to move up into the tip.
Distribution: Place the pipette tip at an angel of 10 to 45 degrees against the inside wall of the receiving vessel. Depress the plunger smoothly to the first stop position.
Purge: Wait one second, then depress the plunger to the second stop position. This “blow-out” stroke removes any remaining sample from the tip. Remove the pipette tip by sliding it up against the vessel wall.
Home: Allow the plunger to move up to the rest position. After transferring your liquid, you can eject the tip and start anew.

To ensure maximum accuracy, please consider the following: operator consistency, pipettes are calibrated “to deliver” and not to “contain”, and pipettes should be calibrated at periodic intervals.

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