Proper use and care of pipetters

What is a pipette?

A pipette is any type of narrow tube used to move small amounts of liquid. There are many types of pipettes available but we will discuss only two types, volumetric pipettes and air displacement pipettes.

Volumetric pipettes

Most of you are familiar with glass or plastic volumetric pipettes that are calibrated to deliver specific volumes. These types of pipettes require the use of a bulb, to create a vacuum that draws the liquid into the pipette. The pipette has markings for a range of volumes. Once the pipette contains the volume of liquid required, it is transferred to a new vessel, and the liquid in the pipette is released. Pipettes that are specified to deliver (TD) are not blown out. If they are specified to contain (TC) they are blown out. We will use volumetric pipettes primarily for volumes between 1 and 10 ml.

Air displacement pipettes

Air displacement pipettes, often referred to as pipetters, are generally used for smaller volumes of liquid, from 1 ml to as little as 0.1 ul (0.0001 ml). Pipetters are used with disposable tips, so that the instrument itself is never in contact with liquid. The pipetter contains a piston in a cylinder or a capillary tube that moves to an appropriate position when the volume is set. When an operating button is depressed the piston moves so that the set volume of air is expelled from the pipette. The disposable tip is placed in a liquid and the button is released, creating a vacuum that pulls the set volume into the tip. Depressing the button again will force the liquid out. With displacement pipettes, there is always a specified volume of air between the pipette piston and the liquid.

Proper use of the Gilson Pipetman®

Countless brands of air displacement pipettes are now produced. They differ primarily in the range of volumes they can handle, and in how the volume is set. In this lab we use mainly Gilson Pipetman® models. When used properly these pipetters deliver set volumes accurately and precisely. Used improperly, accuracy and precision are compromised, and the instrument itself may be damaged. Remember, these instruments cost $400 to $500 a piece. Replacing broken pipettes means less money in the budget to do interesting experiments.

Parts of a Pipetman®

Before reading on, familiarize yourself with the Pipetman® parts as shown in Figure 1.

Figure 1. Parts of the Pipetman® (from Gilson guide to pipetting). Click image for larger view.

Volume ranges of Pipetman®

Each model of pipetter has a specified volume range it will handle. The volume ranges for Pipetman® models are listed in Table 2. We may not use all the models indicated in this table. Never use a pipetter outside of its prescribed volume range, it will not pipette accurately and you can compromise the calibration.

Table 2. Volume ranges for Gilson Pipetman®

P1000 200 – 1000 µl (0.2 – 1 ml)
P200 20 - 200 µl (0.02 ml - 0.2 ml)
P20 2 - 20 µl (0.002 ml - 0.002 ml)
P10 0.5 - 10 µl
P2 0.1 - 2 µl

Selecting a disposable tip for use with the Pipetman®

The Pipetman® itself never should touch any liquids. It is designed to have a disposable tip on the end of the tip holder. Liquid is drawn into the disposable tip. These tips are discarded after being used (into a disposal bucket) by pressing the tip ejector button. Your lab instructor will point out which tips should be used with each model. Generally, tips will only fit on the pipetter they work with, so if the tip fits you should be ok.

Adjusting the volume

Having selected the correct Pipetman® model, you need to adjust the volumeter. For all Pipetman® models the volumeter display shows 3 numbers. This display reads from the top down. How this display is interpreted depends on which Pipetman® you are using (see Figure 3 for examples).

To adjust the volume, turn the push-button or the thumbwheel. On older Pipetman® only the thumb wheel will adjust the volume. For the best accuracy the volume indicator must be in your direct line of site when setting the volume.

Figure 2. Example of volume settings for Pipetman® (from Gilson guide to pipetting).

Drawing up liquid

Before you begin drawing up liquid, notice that there are two stops when pressing down gently on the push-button (Figure 4). The first stop is subtle and is reached just before you completely depress the button. The second stop is when the push-button is depressed as far as it will go. Use the first stop when you are expelling the air from the pipetter in preparation for drawing up liquid. Press to the second stop only when you are expelling liquid from the pipetter.

Figure 3. First and second stops on the Pipetman® (from Gilson guide to pipetting).

Detailed steps for accurately drawing up and dispensing liquid

  1. Select the appropriate pipetter model for the volume you require. Adjust the volume setting. Attach the appropriate tip to the tip holder. [Make sure the tip is firmly on the tip holder.]
  2. Depress the push-button with your thumb until you reach the first stop. Hold the push-button in this position and keeping the pipetter as close to vertical as you can, place the disposable tip into the liquid to about 3 mm deep. [If your tip is immersed too deeply, droplets will form on the outside of the tip, resulting in a larger volume being transferred than you planned. If the tip is not immersed deeply enough, you will end up drawing air as well as liquid and your sample will be too small.]
  3. In a smooth controlled movement allow the push-button to return to its starting position. You may need to move the tip down as you draw up liquid to keep it 3 mm below the surface of the liquid. When the push-button has reached the starting position wait one second so that all the liquid has time to move up into the tip. [Do not let the push-button move up too quickly, this will result in liquid 'jumping' into the tip and possibly being drawn up into the tip-holder.]
  4. Place the tip at an angle (10 to 45 º) against the inside wall of the receiving vessel, so that the tip contacts the wall. Depress the push-button smoothly to the second position (this is the 'blow-out'). Again wait 1 second to make sure all the liquid is expelled. Remove the tip by sliding it up the wall of the vessel.
  5. After the tip has been removed from the vessel you can allow the push-button to move back to the rest position.


Keep pipetters upright at all times when a tip is attached. Never lay them down on your bench or turn them upside down when a tip is attached. If there is liquid in the tip it will run into the tip holder and damage the seal. Once the seal is damaged the pipetter will no longer work correctly. This applies to pipetting aids attached to volumetric pipettes.

Never adjust a Pipetman® outside of its allowed volume range – it will not pipette accurately outside this range and you will damage the pipetter.

Do not drop pipetters on the bench or floor.

Before using your pipetter visually check it to make sure it looks clean. Especially check the end of the tip holder for any evidence of liquid contamination. If the pipetter looks damaged, or if you have accidentally drawn liquid into the tip, bring it to the attention of your lab demonstrator immediately. It may not work correctly and could jeopardize your experiment.

Accuracy and precision

As with any measuring device, a pipetter is not 100% precise each and every time you draw up a volume. It is important to regularly check that a pipetter is working within its specifications, as indicated by the manufacturer. There are two such specifications, accuracy and precision. Accuracy refers to how close the real volume is to the set volume. Precision refers to how similar multiple measurements of the same volume are. It is possible for a pipetter to be precise, but not accurate, or accurate, but not precise.

The most commonly used method to check the accuracy and precision of pipetters is gravimetric. This method is based on the principle that given a certain mass of water and its specific gravity, the volume can be calculated.
At 4°C pure water has a density of about 1 g/cm3 or 1 g/ml. Waters density is also dependent on the air pressure. These two factors are combined to create a Z factor, used for converting the weight of a volume of water to its actual volume. To determine Z factor, simply use Table 2.

Table 2. Values of the conversion factor Z (µl/mg) as a function of temperature and pressure for distilled water.

More information

(links open in a new page)

That's not how you pipette
Pipetman Neo® User Guide
Video - using a pipetman. Excellent review, worth watching all the way through.
And for fun - if you read to the end.

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