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Graduated pipettes are used to transfer liquid and allow the user to determine the volume being removed. They have lines that specify and measure the volume of liquid being transferred. Different suction aids can be used, and accurate volume measurements require the meniscus to rest on top of the graduation line.
In a laboratory, pipettes are used to transfer liquid between different places. There are many different types of pipettes that vary in their accuracy when it comes to measuring the volume of liquid being transferred. A graduated pipette is a type of pipette that allows the user to determine the volume of liquid being removed.
This tool is also called a Mohr pipette, named after Karl Friedrich Mohr, a 19th-century pharmacist. Mohr is said to have developed the graduated pipette so that he could specify the volume of liquid he wanted to transfer. The word “graduated” refers to the series of lines located at specific intervals that run the length of the pipe. These lines allow the user to specify and measure the volume of liquid being transferred. Graduated pipettes are more accurate than Pasteur pipettes, but not as accurate as volumetric pipettes.
Pipettes are long cylinders usually made of plastic or glass. They are tapered at one end, which is where the liquid is drawn in and out of the pipette. All pipettes, including graduated ones, are available in a variety of sizes, so you can transfer different volumes.
To draw liquid into a graduated pipette, some sort of aspiration aid must be attached to the non-tapered end. There are three types of suction aids that can be attached to the pipette, namely a rubber bulb, a pipette pump and an electronic dispenser. The most basic appliance is the rubber bulb, with pipette pumps and electronic dispensers that allow the user more control so more precise volumes can be measured and dispensed.
To determine the volume of dispensed liquid, the user must calculate the difference in the level of the liquid in the graduated pipette before and after dispensing into the new container. To ensure accurate volume measurements, it is important that the meniscus rests on top of the graduation line. A meniscus is the bottom of the arc formed by the liquid inside the pipette.
The graduations are numbered from zero at the top to the largest number at the bottom. For example, if a person wants 10 milliliters of liquid and uses a 10 milliliter (ml) graduated pipette, he will fill the pipette to the zero line at the top of the pipette. To dispense 10 mL, the user should release the suction aid so that liquid flows out of the pipette until the meniscus is on the graduation labeled 10.
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