Pipettes are used to transfer liquid carefully.
In a laboratory, pipettes are used to transfer liquid between different locations. 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.
Pipettes and micropipettes are chemical droppers used to measure and dispense exact amounts of liquids.
This instrument is also known as a Mohr pipette, named after Karl Friedrich Mohr, a 19th-century pharmacist. Mohr would have developed the graduated pipette so that he could specify the volume of liquid he wanted to transfer. The word “graded” refers to the series of lines located at specific intervals that run the length of the tube. 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.
Most modern graduated pipettes are filled using a pump or electronic dispenser.
Pipettes are long cylinders usually made of plastic or glass. They are tapered at one end, which is where liquid is drawn in and out of the pipette. All pipettes, including graduated ones, come in a variety of sizes, so different volumes can be transferred.
To aspirate the liquid into a graduated pipette, some sort of suction aid must be placed on the end that is not conical. There are three types of suction aids that can be attached to the pipette, which are a rubber bulb, a pipette pump and an electronic dispenser. The most basic device is the rubber bulb, with pipette pumps and electronic dispensers that allow the user more control so that more accurate volumes can be measured and dispensed.
To determine the volume of liquid dispensed, the user must calculate the difference in liquid level found in the graduated pipette before and after it is dispensed into the new container. To ensure accurate volume measurements, it is important that the meniscus is at the top of the graduation line. A meniscus is the lower part of the arch that is formed by the liquid inside the pipette.
Graduations are numbered from zero at the top to the highest number at the bottom. For example, if a person wanted 10 milliliters of a liquid and was using a 10 milliliter (ml) graduated pipette, they would fill the pipette to the zero line at the top of the pipette. To dispense 10 ml, the user must release the suction aid so that liquid comes out of the pipette until the meniscus is seated at the graduation marked 10.