Pipette – Definition, Principle, Parts, Procedure, Applications

A pipette is a fundamental laboratory instrument used across biology, chemistry and clinical labs to accurately measure and transfer small volumes of liquid. In this comprehensive guide we’ll explore what a pipette is, the working principle behind air-displacement vs positive-displacement pipettes, the key components of a pipette, the many types you’ll encounter (Pasteur, graduated, volumetric, repeater, multichannel), the correct operating procedure, and the real-world applications of pipettes in cell culture, microplate assays, analytical chemistry and more. We also cover advantages, limitations, and best-practice precautions so you can pipette with confidence and precision.

What is Pipette?

• A Pipette can define as a laboratory instrument used for transferring small measured volume of liquid from one container to another, it’s mostly used in biology and chemistry labs.
• The Laboratory Pipette was designed for accurate measurement and precise liquid handling, it allows the scientist to take exact volume which is required in experiment / test.
• In many laboratories, Micropipette used when very tiny volume (like µL range) is needed, they provides high accuracy but must be handled carefully because pressure and angle can affect readings.
• The concept of Pipette was first seen around the late 19th century, after that improved designs like Pasteur pipette, serological pipette, and later the micropipette were developed for modern lab use.
• Importance of pipette in laboratory works can’t be ignored, as without it proper quantitative results can’t be obtained, it plays vital role in microbiology, biochemistry, molecular works etc., for preparing solutions and dilutions accurately.
• As technology moved forward, adjustable micropipettes were invented that allowed researchers to change volume easily, which make laboratory works more flexible and repeatable.
• After that, different type of pipettes were created for special purpose – for example air displacement type, positive displacement type – all aiming for more precision and control in liquid transfer.
• It can be said that Pipette became one of the most important tools of laboratory science, because by them experimental error is minimized and reproducibility is maintained which prevail contamination also.
• Many laboratory pipettes are now ergonomic, lightweight and digital, still the principle of operation remain same — liquid is aspirated and dispensed through a narrow tube using vacuum / air pressure system.
• Overall, the Pipette whether mechanical or electronic, it shows how small innovations changed laboratory working style forever, and that’s why it’s considered heart of many laboratory procedure today.

Definition of Pipette

A pipette is a laboratory tool used to measure and transfer small volumes of liquid with precision.

Principle of Pipette

• The​‍​‌‍​‍‌​‍​‌‍​‍‌ Pipette principle involves the control of air displacement or direct piston contact for the aspiration/dispensing of a liquid, the operation is achieved by the piston movement inside a cylinder, this movement causes a vacuum and the liquid is sucked in through the tip (usually in µL scale).
• In the case of an air, displacement Micropipette, the air cushion is created between the piston and the sample, and the volume transferred is determined by the piston travel (set by volume control), which indicates the exact volume to be moved.
• Positive, displacement pipettes are the ones that should be used in the case of volatile or viscous liquids, as the piston makes direct contact with the liquid, the evaporation and carry, over are minimized.
• Temperature, tip, fit, immersion depth, plunger speed, and operator technique affect Precision and accuracy, therefore calibration and consistent method are necessary to maintain reproducibility.
• Small systematic errors are caused by air, compression (and by vapor pressure of liquid), thus it is suggested that regular calibration and good technique be followed. These, in turn, ensure the correct volume.
• The volume setting is changed by turning or moving the volume control, a stop or limit is usually there to prevent over, aspiration, and some models show digital readouts.
• To prevent contamination, disposable tips are used, they are ejected after the use (tip), this procedure facilitates sterility, however sometimes, it does not completely prevent contamination.
• During micropipette work, the internal air column is slightly compressed when the tip is inserted, this compression causes a small error if the immersion depth or speed changes, so it is suggested that the tip be pre, wetted and the angle kept constant.
• The principle can be considered as a controlled displacement (air or piston) step resulting in suction and then in dispensing, with predictability being the result of calibration, correct tips, and steady handling.
• Practically, the user should pay attention to the angle (vertical vs slanted), pre, wetting, plunger action being smooth, as these small actions affect measurement and ​‍​‌‍​‍‌​‍​‌‍​‍‌precision.

Parts of Pipette and their functions

1. Plunger Button– It used for aspirating and dispensing the liquid; when pressed, piston moves down creating air displacement which draw or release liquid by the tip.
2. Adjustment Knob / Volume Control – Volume of liquid to be handled is set by this knob, and it allows accurate selection of µL or mL range, but sometimes reading may differ if rotated too fast.
3. Piston Mechanism– Located inside pipette body, it creates suction or pressure; movement of piston defines how much air and liquid displaced, thus main part of working principle.
4. Tip Cone /Nozzle – Lower narrow part where disposable pipette tip is attached, it must be airtight otherwise leakage occurs which affect accuracy and precision badly.
5. Disposable Tip – Made of plastic (polypropylene), attached at bottom end, used for taking the sample and then ejected after use to avoid contamination / cross mixing between solutions.
6. Ejector Button / Tip Ejector– This part removes the used tip automatically by pressing, so user don’t touch tip directly, keeping safety and sterility of laboratory pipette.
7. Digital Display/ Window – Present in adjustable micropipettes, it shows the selected volume (e.g. 10 µL, 100 µL etc.), helps user to set correct reading fastly and reduce errors.
8. Body/ Barrel– Main cylindrical structure that holds internal parts like piston and spring, mostly made from durable plastic or metal alloy to ensure sturdy and hardy construction.
9. Spring Assembly– Provides restoring force to piston and maintains consistent motion, so that same volume is aspirated every time, though after long usage it may lose elasticity.
10. Sealing O-Ring– Located between piston and cylinder, it ensures air-tight sealing, helps in smooth operation and reduces friction while aspirating the sample.

Types of Pipette

There are present 1 Types of Pipette, such as;

1. Volumetric Pipette – A single calibrated bulb pipette that is used for delivering one exact volume, and it is relied for high precision in analytical work, its neck is narrow and reading is by single mark.

2. Graduated Pipette – A long tube with many graduation marks that allows variable volumes to be measured, they are less precise than volumetric, but more flexible for general lab uses.

3. Serological Pipette – A glass or plastic pipette with graduations to tip which is usually used with a rubber bulb or pipette controller to expel liquid completely, commonly used for cell culture and general lab transfer.

4. Mohr Pipette – Similar to graduated but calibration stops before tip so partial delivery is required, it is chosen when incomplete discharge is intended, used in titration/biochemical tasks.

5. Pasteur / Transfer Pipette – A simple narrow stem with rubber bulb, used for quick transfer of liquids where high accuracy is not required, disposable plastic types are widespread in modern labs.

6. Micropipette – Small volume Micropipette (0.1 µL – 1000 µL) is operated by piston (air-displacement) and is extensively used in molecular biology, they are provided as single or multi-channel versions.

7. Positive-displacement Pipette – A pipette where piston contacts liquid directly (not an air cushion), used for viscous or volatile samples, contamination and evaporation are reduced by design.

8. Electronic Pipette – Motor-driven micropipette that is powered by battery and programmed for dispensing, it is used to reduce repetitive strain and improve consistency in high-throughput work.

9. Repeater / Dispenser Pipette – A device for repeated dispensing of same volume many times without refilling, ideal for serial dilutions, plate-work and repetitive assays, it saves time and improves uniformity.

10. Single-channel – A pipette with one dispensing channel that is used for individual samples, it can be adjustable or fixed-volume and is widely used in routine laboratory pipetting.

11. Multi-channel – A pipette with 8 or 12 channels, used for microplates (96-well etc.) to speed up workflows and ensure parallel dispensing, it is essential in diagnostic and high-throughput labs.

Pipette Procedure

1. Before use, the Pipette and tips are inspected for damage, cleanliness and proper fit, and the calibration status is checked against lab record to ensure accuracy.
2. The correct tip (size and type) is selected and is firmly attached to the tip cone, a loose tip will cause leakage and volumetric error.
3. The desired volume is set on the Micropipette by rotating the volume control and the digital/readout window (if present) is verified to match required µL (or mL) value.
4. The tip is pre-wetted by aspirating and dispensing the same liquid 2–3 times, this conditions the air column and reduces systematic error when the sample is finally taken.
5. For aspiration, the plunger is depressed to the first stop, the tip is immersed 1–3 mm into liquid (or deeper for viscous liquids) and the plunger is released slowly to aspirate sample, immersion depth and speed must be steady.
6. The pipette is withdrawn from the source, any droplets on outside of tip are touched to vessel wall to remove them, then the pipette is moved to the receiving vessel without delay to avoid evaporation / loss.
7. To dispense, the plunger is depressed smoothly to first stop to deliver main volume, and then pressed to second stop (blow-out) to expel residual liquid when blow-out tip is used, some protocols require the blow-out, others not.
8. When dispensing against the wall of receiving container, the tip is held at an angle and close to surface to avoid splashing, the tip is withdrawn while still depressed to second stop if required by technique.
9. After dispensing, the ejector button is pressed to discard the used tip into appropriate waste (biohazard or sharps as applicable), tips should not be reused unless procedure specifically allows it.
10. For viscous, volatile or heated samples, a positive-displacement pipette or special tips are chosen, because direct piston contact reduces evaporation and carry-over, this improves accuracy.
11. Periodic Calibration and performance checks (gravimetric method or dye check) are performed and records are kept, if deviation is observed recalibration or servicing is arranged, do not assume pipette is fine.
12. Good technique is practiced: consistent immersion depth, steady plunger speed, pre-wetting, vertical vs angled handling as required, and training is provided to users, they will improve reproducibility and prevail contamination.
13. At end of use, the pipette is cleaned (external surfaces wiped), stored vertically on rack, batteries charged if electronic, and service intervals are noted to prolong life and maintain precision.

Applications of Pipette

• Pipette is mainly used for accurate measurement / transfer of small volumes of liquid in laboratory experiments.
• It is applied in clinical laboratories where blood serum or plasma are taken for biochemical analysis like glucose, enzyme, etc.
• In microbiology, it used for transferring culture broth and inoculum by aseptic way to another tube or flask.
• It is used for preparing reagent solutions, dilutions and serial dilution which is often needed for microbial counting and enzyme assays.
• The pipette are applied in chemical laboratories for titration and volumetric analysis, to know concentration of unknown solution.
• Molecular biology work are carried by pipette for adding DNA / RNA samples, buffer, restriction enzyme, and others small reagents in PCR tubes.
• Used in biochemical experiment, like enzyme kinetics where exact concentration and time matter for reaction rate.
• In pharmaceutical industry, pipette used for formulation and testing of drugs (mainly liquid drugs).
• It is also used for transferring media in culture preparation, mostly when bacteria like Escherichia coli are sub-cultured.
• Sometimes pipette are employed in environmental studies, for taking water or effluent sample for pollution test.
• After calibration, it can used in quantitative estimation, though human error prevail accuracy sometimes.
• In research laboratories, pipette are helpful for preparing standards and control samples for analysis of proteins, enzymes, etc.
• The pipette is also applied in food technology for checking nutrient content or contamination in food sample.
• Used for adding indicators or titrant dropwise in analytical chemistry experiment.
• Finally, pipette helps in maintaining precision and reproducibility in almost all wet lab works where volume control are important.

Advantages of Pipette

• The pipette gives very accurate measurement of small volume liquid, which is very important in laboratory experiments.
• It can be easily handled and operated, even by beginner person after some practice.
• Reproducibility of result are obtained since each volume taken is nearly same every time.
• It helps to reduce contamination because liquids are drawn directly without touching external surface.
• Pipette is suitable for different laboratory works – like biochemical, clinical or microbiological test etc.
• The precision and reliability of pipette are higher compare to other manual methods of liquid transfer.
• After calibration it can maintain constant accuracy even for long period if it’s used carefully.
• It allows easy calibration / adjustment, thus error during measurement can be minimized.
• Less sample wastage occurs since small amount is used effectively in each experiment.
• It provides quick transfer of liquids, saving both time and effort in repetitive task.
• In molecular biology, pipette ensures proper addition of reagents, enzymes, or buffer that need exact quantity.
• Pipette are available in different type (like micropipette, serological pipette) making them flexible for many purposes.
• It can be sterilized easily by autoclaving or alcohol wiping, thus safe for reuse in microbiological works.
• The design of modern pipette are ergonomic, reduces hand strain and makes continuous use more comfort.
• Using pipette makes experiment more systematic and reliable, so scientific accuracy can prevail better results.

Limitations of Pipette

• Accuracy of pipette highly depend by user handling, small mistake can cause large error in measurement.
• It need proper calibration, otherwise volume taken not remain same every time.
• Pipette are limited in volume range, so large volume liquid can’t be handled by it easily.
• The formation of air bubbles inside the tip may disturb precision of liquid transfer.
• It’s sensitivity affected by temperature and viscosity of liquid, giving inconsistent reading sometimes.
• Pipette can be easily damaged if dropped or used roughly, plastic ones bend and glass may break.
• Human error are common because manual operation are required for every aspiration and dispensing step.
• It is expensive equipment specially the micropipette which need regular maintenance.
• Pipette requires frequent cleaning and sterilization, otherwise contamination of samples may occurs.
• The accuracy get affected when tip not fitted tightly or reused many times.
• Calibration process is time consuming, and sometimes skipped in busy laboratories.
• Pipette can’t used for viscous / volatile samples effectively because leakage or incomplete delivery happen.
• It’s maintenance cost higher than other simple liquid transferring devices like dropper or burette.
• Some users find hand fatigue or discomfort when used continuously for long time.
• Thus, although pipette gives good accuracy, their performance prevail limitations when care not taken properly.

Precautions

• Mouth pipetting should never be done, because it can cause serious infection or accident by chemical intake.
• Always use pipette aid / filler bulb for drawing the liquid safely and accurately.
• The tip of pipette must be checked properly before use, it should be clean, dry and free from any crack.
• Pipette must be held vertically, as tilting may cause wrong volume measurement.
• Air bubbles should be avoided during aspiration, they disturb the accuracy of liquid volume.
• Before use, pipette has to be calibrated properly, otherwise the volume reading may not be correct.
• The liquid should be released slowly and smoothly, to avoid splashing or sticking inside wall.
• Always select correct pipette size for the required volume, using wrong one can affect precision.
• Pipette should be cleaned immediately after use, especially when corrosive / viscous liquids are used.
• During filling, never insert pipette tip too deep inside container as it may contaminate solution.
• The outside surface must be wiped gently with tissue paper if any liquid attach externally.
• Pipette should not be held horizontally for long, liquid may enter the filler and damage it.
• Avoid using broken or chipped pipette, it may cause injury or leakage of solution.
• While transferring biological samples (like blood or serum), proper sterilization must be maintained.
• Store the pipette in upright position after cleaning, so that moisture drain completely before reuse.
• Never use too high temperature liquids, as it may deform plastic pipette or affect calibration.
• It’s important that tips fit tightly, otherwise leakage and loss of accuracy will happen.
• Regular inspection and maintenance of pipette should done to prevail operational problem.
• During pipetting, avoid touching the tip to any surface to minimize contamination risk.
• Always follow laboratory safety rule, wearing gloves and coat when handling any hazardous liquids.

FAQ