Pipettes are the calibrated laboratory equipment used to handle liquids. Many kinds of pipettes are used in the laboratory, like micropipette, glass pipette, automated pipette, etc.
Among those, glass pipettes are one of the liquid handling instruments carrying utmost significance due to their precision. These are useful in handling samples with volume in milliliter (ml).
Glass pipettes are of different types, and handling of glass pipettes requires an attached filler (pipette bulb or pipette filler) at the top for filling the liquids. They have uses in various sectors like chemical laboratories, biochemistry laboratories, forensic science, microbiology laboratories, etc.
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Types of Glass Pipettes
The glass pipettes generally used have three types; graduated, non-graduated, and Pasteur pipettes.
Graduated glass pipettes are the type of pipettes that has increments marked along the straight glass tube. Its another name is measuring pipette. It is further classified into two types based on the graduation mark and nominal volume it can pipet; Mohr’s and serological pipette.
- Mohr’s pipette: A Mohr’s pipette is used as a drain-out pipette. It is a straight tube having a graduation mark at each 0.1 ml interval. The first graduation mark begins well past the bottom of the tip. The broken tip can disrupt the precision of handling the liquid.
- Serological pipette: A serological pipette is used as a blow-out pipette. It is a straight tube with a graduation mark near the tip. A slight pressing of the bulb is necessary at the end of dispensation for accuracy.
Likewise, based on construction, pipettes are of three types; type 1, type 2, and type 3.
- Type 1: These have nominal values at the bottom and can deliver liquid samples partially only for all the values.
- Type 2: These have nominal values at the top of the pipette and the highest value below.
- Type 3: These are like type 1 in construction, but they can deliver fluids completely only in nominal value.
Similarly, based on the accuracy, the graduated pipettes are of class A, class As, and class B. Class A and As are very accurate because they have specified error ranges. In contrast, class B is less accurate because it has double the general error limits.
Non-graduated pipettes are the pipettes that lack the increment of graduation mark in the tube. The other denotation of a non-graduated pipette can also be a volumetric pipette, a bulb pipette, or a transfer pipette.
Pasteur pipettes are called an eye dropper or a dropper. Its construction is either with glass or plastic material. The tip end tapers to a narrow opening in the Pasteur pipette. There is a bulb at the top of the pipette in the case of plastic and glass Pasteur pipette needs a rubber bulb for withdrawing liquid. A teat pipette is the combination of a glass pipette and a rubber bulb.
Parts of Glass Pipettes
The parts of glass pipettes are as follows:
- Orifice of the tip: It is the pointed end of the pipette and comes in direct contact with the liquid.
- Calibration details: It is an area in the pipette above the graduation mark. It has the imprinted details about the manufacturer, volume range (measuring) or nominal volume (bulb pipette), tolerance volume, calibration temperature, standard applied for calibration, and waiting time.
- Color rings: Color rings or color bands is a code to identify the nominal volume of the pipette by some companies.
- Suction end: It is the top part of the pipette, where the pipette filler or bulb can attach for aspirating and dispensing the liquids.
- Additional parts:
- The bulb pipette has a volume mark for pipetting or transferring the correct amount of liquid volume.
- The blow-out or serological pipette has a blow-out ring near the topmost or suction part of the pipette.
Handling of Glass Pipettes
While handling glass pipettes, one should never aspirate fluids in the laboratory from the mouth. A pipette bulb, rubber bulb, or filler is used for aspirating.
A pipette bulb is made up of rubber, so it is also called a rubber bulb. It is used to safely fill the pipette with liquid in the laboratory, hence named pipette filler. The generally used pipette filler are general purpose bulbs, three-valve bulbs, and thumb wheel type fillers (made of plastic).
Steps for using three valve pipette bulb:
- Attach the pipette at the insertion part.
- Release air from the pipette by pressing valve A and the bulb simultaneously to create a vacuum.
- Insert the pipette tip into the liquid container.
- Press the S valve at the bottom to aspirate the liquid with the help of the vacuum created.
- Place the pipette tip into the desired container to dispense the liquid and press valve E.
Filling the Liquid
- Fill the pipette with pipette filler approximately above 5 mm of the mark.
- Then, adjust and bring the liquid to the graduated mark.
- Set the meniscus at the mark (for colorless liquid, the upper meniscus, and the colorful fluid lower meniscus).
- Remove excess liquid from the tip for precise delivery.
Dispensing the Liquid
- Place the tip of the pipette into the container.
- Press the filler to dispense all the liquid.
- Wait for a few seconds when the liquid reaches the tip (based on the company’s guidelines).
- After the wait time, draw the pipette upwards by touching the wall to dispense the remaining liquid. Do not blow out the remaining liquid.
Uses of Glass Pipettes
The glass pipette has broad utility in almost all science laboratories. Some fields with the use of glass pipettes are as follows:
- Chemistry laboratory: It is used in transferring liquids during various processes. The volumetric pipette is helpful in different tests relating to volumetric analysis.
- Pharmaceutical industry: Glass pipettes in the pharmaceutical industry have utility in drug production. It is used to transfer measured volume in during quality control as well.
- Microbiology laboratory: Like droppers, glass pipettes transfer different chemicals in milliliter (ml) in various experiments.
- Biochemistry laboratory: The primary uses of glass pipettes in the biochemistry laboratory are as follows:
- For preparing buffer solution.
- To transfer the solution for conducting different biochemical tests.
- For accurate measurements of the chemicals.
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