Pasteur pipettes, also known as droppers or eye droppers, are used to transfer small quantities of liquids. They are usually glass tubes tapered to a narrow point, and fitted with a rubber bulb at the top. The combination of the Pasteur pipette and rubber bulb has also been referred to as a teat pipette. Pasteur pipettes come in various lengths and are usually sold in boxes of hundreds. They are named after the French scientist Louis Pasteur, who was known to have used a variant of them extensively during his research. In the past, there was no equipment to transfer a chemical solution without exposing it to the external environment. The hygiene and purity of chemical compounds is necessary for the expected result of each experiment. The Pasteur pipette, both glass and plastic types, are sterilized and plugged with a rubber bulb at the open end of the pipette preventing any contamination from the atmosphere. Generally, they are considered cheap enough to be disposable, however, so long as the glass point is not chipped, the Pasteur pipette may be washed and reused indefinitely.
The name eye dropper also may refer to early models of fountain-pens, which have to be refilled with some kind of Pasteur pipette.
It is not recommended to use pasteur pipettes for work involving accuracy since pasteur pipettes are not designed to measure specific volume; however, it can be used to add drops of reagents. Before using a pasteur pipette, the tip should be carefully examined for cracks. To increase accuracy, the pipette is to be rinsed with the reagent. To use the pipette, squeeze the bulb to expel air out of the pipette and submerge the tip of the pipette to the solution vertically. Gently relax the bulb to draw the solution up and make sure that the solution does not overshoot into the bulb contaminating it. To dispense the reagent, hold the tip against the side of the target container at a 30 to 45 degrees angle.
Glass Pasteur pipettes
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Nowadays, the two types of glass that are used mainly in the laboratory and in the Pasteur pipette are borosilicate glass and soda lime glass. Borosilicate glass is a widely used glass for laboratory apparatus, as it can withstand chemicals and temperatures used in most laboratories. Borosilicate glass is also more economical since the glass can be fabricated easily compared to other types. Soda lime glass, although not as chemically resistant as Borosilicate glass, are suitable as a material for inexpensive apparatus such as the Pasteur pipette.
Plastic Pasteur pipettes
Plastic Pasteur pipettes, also referred to as transfer pipettes, have their stems and bulbs in the form of a single piece made of plastic. They commonly come in 1, 2, 3, and 5 ml which comes with a specific drop size of 10, 20, 25, 35, and 50 µl. The volumes are usually marked on the stem, though the markings are rather crude and are not particularly accurate.
As plastic Pasteur is relatively inexpensive and disposable, they are often used to avoid cross-contamination. In a solution containing cell and/or protein, it reduces the loss of cell and/or protein that binds to glass. The designation of the plastic pipettes contain the long flexible tube. It can be bent for drawing solution from small volume tubes.
Plastic Pasteur pipettes are often used in biology where most media are aqueous and solvent resistance is not important. (Most organic solvents, such as hexane and acetone cannot be used in plastic Pasteur pipettes as the solvent can dissolve the plastic.) The pipettes are also hard to wash and are usually discarded with other biohazard waste after each use.
Plastic bulb pipettes are generally not precise enough to be used for exact measurements, whereas their glass counterparts can be extremely precise.
- Microscale column chromatography
The constriction toward the tip of the Pasteur pipettes may be plugged with a bit of tissue paper or cotton wool to filter off solids from small amounts of liquids. The bulb can be attached and squeezed to help viscous solutions filter more rapidly.
With a bit of skill, Pasteur pipettes may also be used for microscale column chromatography. With appropriately fine silica gel, the bulb may be squeezed for microscale flash column chromatography.
- Microscale distillation
Pasteur pipettes can also be used for microscale distillation. The liquid to be distilled is placed into a small reaction tube along with a boiling chip and heated to reflux one-half to two-thirds of the way up the inside of the tube. After squeezing the bulb to expel air, a pasteur pipette is inserted into the tube just below the level of the ring of refluxing liquid (into the vapor). The vapor is then drawn into the relatively cold pipette tip, causing it to condense and accumulate inside of the pipette.
- Microscale liquid storage
Heat can be applied to the tip of a plastic Pasteur pipette to seal the solution and create a liquid-tight storage.
Medical Laboratory required high efficiency and precision for drug test and observation of diseases. Pasteur pipettes are commonly used in the medical lab because of its essential accuracy. The design of the Pasteur pipette allows for high effective performance in the medical lab. It produces a constant volume of drop. This reduces the concern of liquid remaining in the pipette.
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