Pipettes are special type of long narrow tubes, open at both ends, which are used for fluid column measurements. Their upper end is wide which is used for applying suction pressure and lower end is tapering which is used for drawing in or releasing the fluid. They are calibrated to indicate the volume. They can be made of glass or plastic.
Depending upon their size they are divided into macro pipettes that have a capacity of 1 ml or more and micropipettes that have a capacity up to 1 ml.
TYPES OF PIPETTES
1. Volumetric Pipettes:
Purpose: Volumetric pipettes are designed for precise measurement and transfer of a specific volume of liquid.
Design: They have a single calibration mark, typically near the top, and a tapered tip. To dispense the intended volume, the liquid is drawn up to the calibration mark and then delivered.
Purpose: Micropipettes are used for accurately measuring and transferring very small volumes of liquid, usually in the microliter (μL) range.
Design: Micropipettes are adjustable and come in various configurations. They have a digital or analog display to set the desired volume. They are available as single-channel or multichannel pipettes for dispensing multiple samples at once.
3. Serological Pipettes:
Purpose: Serological pipettes are mainly used for transferring larger volumes of liquid, such as culture media or reagents, with less precision than volumetric pipettes.
Design: They have graduation markings along the length of the pipette, and the liquid is dispensed by releasing it through the pipette’s tip.
4. Pasteur Pipettes:
Purpose: Pasteur pipettes are versatile tools used for various laboratory tasks, including transferring small amounts of liquid.
Design: They are typically made of glass, have a straight shape with a fine, tapered tip, and are often disposable.
5. Graduated Pipettes:
Purpose: Graduated pipettes are used for measuring and transferring various volumes of liquid when high precision is not essential.
Design: These pipettes have calibration marks along their length, allowing you to select different volumes by aligning the liquid with the desired mark.
6. Disposable Pipettes:
Purpose: Disposable pipettes are designed for single-use applications to prevent cross-contamination and simplify lab work.
Design: They can be made of plastic or glass and are discarded after use, which reduces the risk of contamination between samples.
7. Bulb Pipettes:
Purpose: Bulb pipettes are used for delivering a specific volume of liquid by squeezing a rubber bulb to draw in the liquid and then releasing it to dispense the liquid.
Design: They have a rubber bulb at the top and a tapered tip for controlled liquid delivery.
8. Filter Pipettes:
Purpose: Filter pipettes are employed when filtering and dispensing liquids while retaining particles or contaminants.
Design: These pipettes include an integrated filter in the tip to ensure that only the filtered liquid is dispensed.
9. Repeater Pipettes:
Purpose: Repeater pipettes are suitable for repetitive dispensing of a specific volume of liquid, making them ideal for high-throughput tasks.
Design: These pipettes are often electronic and feature a digital display. They can be programmed to repeatedly dispense the same volume accurately.
10. Positive Displacement Pipettes:
Purpose: Positive displacement pipettes are used when working with viscous or volatile liquids. They use a piston to displace liquid without coming into direct contact with the pipette.
Design: These pipettes have a piston mechanism, and they typically require disposable tips for each use to prevent carryover contamination.
These are used to deliver (TD) or to contain (TC) very small volumes of fluids up to 1 ml.
1. To Deliver (TD):
In this type the pipette when filled up to the upper mark contains that much volume of fluid. It is to be emptied by touching its end against the tube wall in order to deliver that much volume.
2. To Blow out (B):
In this type once the pipette fluid is drained the residual volume of fluid is blown out in order to deliver the required volume. These pipettes have an etched ring near the mouth end with the volume written below it.
3. To Contain (TC):
These pipettes have only one mark on their stem that indicates a specified volume that the pipette contains when filled to that mark. These must be blown to empty. Then the fluid in which the specimen is blown out should be sucked up and down to wash out the whole specimen. The best example is Sahli’s Hb pipette.
The best quality pipettes are called type A pipettes. Others are named as type B, C, D and E respectively. Type D & E are poor quality pipettes.
Delivering the specified volume of mercury with the pipette into a pre-weighed clean glass beaker checks calibration. The beaker is weighed again. The weight of the mercury in mg should be in accordance with the volume in ml.
PRECAUTIONS FOR USE OF PIPETTES
- Suction force should be applied with the help of a rubber bulb, teat or pipette filler attached to the suction end. Mouth pipetting must not be done in any case.
- Once the fluid has been drawn in the pipette to the required level, suction force should be maintained so that fluid is not lost while transferring. If a rubber bulb is used the pressure should be maintained.
- Fluid should be drawn to a slightly higher level than required and the upper end should be immediately covered with the pulp of index finger. Then the level of fluid is adjusted to the required volume by slight release of finger pressure.
- For colored fluids the level of upper meniscus is taken as the indicator of volume while for colourless fluids level of the lower meniscus is taken.
These pipettes comprise a body and a tip. The body contains a precalibrated piston system which when pressed and released sucks a precise amount of fluid in the tip. Disposable tips made of plastic are used and discarded after use. These pipettes are of two types. One type is prefixed for a single specified volume. In other type, the volume can be adjusted within a narrow range. Both the types are available in different volumes with different sizes of tips. These must be checked for their accuracy from time to time because with wearing of spring system their accuracy may be lost. They are best used when very small amounts of liquid are to be delivered very quickly and in precise amount.
AUTOMATIC DELIVERY SYSTEM
In place of pipette this system is available to directly siphon the required amount of fluid from a bottle to another container. The system is directly attached to the bottle containing reagent and adjusted to required volume. It is useful when same amount of same reagent is repeatedly used.
Pasteur pipette is a piece of tube, one end of which is drawn to very narrow diameter and a rubber bulb is attached to the other end. This is used when a fluid is to be delivered in drops of specified volume. These are also called dropping pipettes or droppers and their stem can be graduated for volume indication. Disposable Pasteur pipettes made of plastic are also available. These are useful for handling infections material such as serum etc.