What Is the Purpose of a Pipette?

Volumeric Pipettes

• Pipettes come in two varieties: volumeric and measuring. Designed for transferring specific volumes, volumeric pipettes resemble simple glass tubes. Using a volumeric pipette involves dipping the pipette into a solution and placing a finger over the end, or squeezing a rubber bulb to draw up the specified amount. Different quantities of solution, usually between one and 100 milliliters, require different sizes of volumeric pipette.

Measuring Pipettes

• Measuring pipettes are calibrated into small divisions to provide better accuracy and enable measured quantities as small as one microliter (one millionth of a liter). While some measuring pipettes use both finger and bulb methods to draw up liquids, automatic micropipettes provide better accuracy. Micropipettes use an adjustable plunger, marked with a minimum and maximum volume range, which is set to the required measurable amount.

Using a Pipette

• Regardless of the type of pipette, using them requires care. To prevent damage to the pipette when drawing in a solution, place the pipette1/4 of an inch from the bottom of the container. Once the required volume or measure is contained in the pipette, a gentle touch on the side of the solution beaker removes excess droplets. When transferring the solution, place the pipette at an angle of 10-20 degrees and slowly allow the liquid to drain from the pipette. Again, a gentle touch removes hanging droplets. Do not blow through the pipette to remove excess; calibration of the pipette takes this excess into account.

Cleaning a Pipette

• Pipettes require cleaning after every use to prevent contamination and ensure delivery of the right amount during its next use. To clean, draw distilled water into the pipette and tilt and roll the pipette so that the water contacts with all inside surfaces. Repeat this process twice more, and then rinse the entire pipette in distilled water, before returning it for use.