pipettes

Pipette- Parts, Principle, Types, Calibration, Procedure, Uses

MICROBIOLOGY / By /

Introduction:

A pipette is a laboratory tool that is used to measure and transfer small volumes of liquids. It is a tube with a calibrated tip and a plunger that allows the user to draw a specific volume of liquid into the pipette and then dispense it.

Pipettes are commonly used in scientific research and other laboratory settings to accurately measure and transfer small volumes of liquids, such as samples for analysis or reagents for chemical reactions.

There are several types of pipettes, including manual pipettes, which are operated by hand, and electronic pipettes, which use a motor to dispense the liquid. The volume that a pipette can hold is usually calibrated in microliters (μL) or milliliters (mL).

History:

The invention of the pipette can be traced back to the 17th century, when the first glass pipettes were developed. These early pipettes were made by heating a glass rod and then shaping it into a tube with a narrow tip. The volume that the pipette could hold was determined by the size of the bore (inside diameter) of the tube. In the 19th century, more accurate pipettes were developed that used a calibrated scale on the side of the pipette to measure the volume.

In the 20th century, the development of more precise manufacturing techniques and the use of new materials, such as plastic, allowed for the production of more accurate and reliable pipettes. In the 1960s, the first electronic pipettes were developed, which used a motor to dispense the liquid, greatly increasing the precision and reproducibility of liquid handling. Today, pipettes are an essential tool in a wide range of scientific and medical applications.

Principle:

The working principle of a pipette is based on the principle of fluid displacement. When the plunger of a pipette is pushed in, it creates a vacuum inside the pipette that causes the liquid to be drawn into the pipette. The volume of liquid that is drawn into the pipette is determined by the calibrated markings on the pipette. When the plunger is released, the liquid is expelled from the pipette through the nozzle. The volume of liquid that is dispensed is determined by the position of the plunger when it is released. By using a combination of these two actions, a user can accurately and precisely measure and dispense a specific volume of liquid using a pipette.

The principles of pipette use include accuracy, precision, calibration, liquid compatibility, technique, and maintenance.

Accuracy refers to the ability of the pipette to deliver the volume of liquid that it is calibrated to deliver. This is usually stated as an accuracy range, such as ±0.1 mL.

Precision refers to the consistency with which a pipette delivers the same volume of liquid, even when used multiple times.

Calibration is the process of adjusting a pipette to ensure that it is delivering the correct volume of liquid. This should be done regularly to ensure accuracy.

Different types of pipettes are designed to handle different types of liquids. It is important to use the correct type of pipette for the liquid being measured to ensure that it is delivered accurately.

Regular maintenance, such as cleaning and proper storage, is important to ensure that a pipette is working correctly and delivering accurate volumes of liquid.

Parts:

The several different parts of a pipette are:

Barrel: This is the main body of the pipette. It is typically made of plastic or glass and is designed to hold the liquid being measured or transferred.

Mouthpiece: This is the opening at the top of the pipette where the user places their mouth to create suction and draw the liquid into the pipette.

Graduations: These are markings on the barrel of the pipette that indicate the volume of liquid contained in the pipette.

Tip: This is the small, cone-shaped end of the pipette that is used to dispense the liquid.

Volume adjustment knob: This is a small knob or lever that is used to adjust the volume of liquid that is drawn into or dispensed from the pipette.

Parts of Pipette

Fig: Parts of Pipette

Calibration mark: This is a mark on the barrel of the pipette that is used to calibrate the pipette to a specific volume.

Finger rest: This is a small protrusion near the base of the pipette that is used to help the user hold and control the pipette.

Base: This is the bottom of the pipette, which sits on the surface of the lab bench or other surface when not in use.

Types:

The common different types of pipettes that are used in laboratories are:

Micropipettes: These are small, highly precise pipettes that are used to measure and transfer very small volumes of liquid, typically in the range of microliters (μL). They are commonly used in molecular biology and biochemistry laboratories.

Volumetric pipettes: These are pipettes that are calibrated to a specific volume, and they are used to measure and transfer precise volumes of liquid which are commonly used in chemistry laboratories.

Graduated pipettes: These pipettes have a series of markings along the body that indicate the volume of liquid contained within the pipette. They are commonly used to dispense known volumes of liquid for testing and analysis.

Dispensing pipettes: These are pipettes that are designed to dispense a specific volume of liquid. They are commonly used to dispense reagents or other solutions.

Transfer pipettes: These are pipettes that are designed to transfer small volumes of liquid from one container to another. They are commonly used in laboratories for transferring samples or reagents.

Automatic pipettes: These are pipettes that use a motor or other mechanism to dispense or aspirate liquid, rather than being operated manually by the user. They are commonly used in high-throughput laboratories where a large number of samples need to be processed quickly.

Single-channel pipette: It consists of a plunger that can be moved up and down within a cylindrical tube, called the barrel, to draw in or expel liquid through a nozzle at the tip.

Multichannel Pipettes: It consists of a plunger that can be moved up and down within a cylindrical tube, called the barrel, to draw in or expel liquid through a series of nozzles at the tip. The volume of liquid that can be transferred using a multi-channel pipette is typically adjustable, and is typically set by rotating the plunger to the desired volume marking on the barrel.

Operating Procedure:

The operating procedure for a pipette will depend on the specific type of pipette you are using and the task you are performing. It is also important to follow proper hand hygiene and use appropriate personal protective equipment (PPE) when handling liquids in the laboratory. Below are some general steps for operating a pipette:

  • Choose the appropriate pipette for the volume of liquid you need to measure or transfer. Make sure the pipette is clean and in good working order.
  • Adjust the volume on the pipette to the desired volume. This can be done by turning a knob or lever, or by selecting a volume setting on an automatic pipette.
  • Place the pipette tip into the liquid you are measuring or transferring.
  • Slowly draw the liquid into the pipette by creating suction with your mouth or by using a pipette pump. Be sure to fill the pipette to the correct volume, as indicated by the graduations on the barrel of the pipette.
  • If you are transferring the liquid to another container, carefully position the pipette tip over the container and gently expel the liquid. Avoid splashing or spilling the liquid.
  • After use, properly dispose of the pipette tip and clean the pipette as directed by your laboratory’s procedures.

Calibration:

Calibration of pipettes is the process of ensuring that the volume of liquid dispensed or aspirated by a pipette is accurate and consistent. Calibration is important to ensure the reliability and reproducibility of your measurements and experiments. It is strongly recommended to calibrate your pipettes regularly to ensure their accuracy and reliability. The frequency of calibration will depend on the type and model of the pipette and the demands of your laboratory. It is generally recommended to calibrate pipettes at least once a year, or more frequently if they are used frequently or subjected to rough handling. In addition, it is important to follow proper hand hygiene and use appropriate personal protective equipment (PPE) when handling liquids in the laboratory and follow the manufacturer’s instructions and any relevant guidelines or regulations when calibrating pipettes.

There are several different methods for calibrating pipettes, depending on the type and model of the pipette and the level of accuracy required.

Gravimetric calibration: This method involves weighing a known volume of liquid and comparing it to the volume indicated by the pipette. This method is most suitable for volumetric pipettes and is the most accurate method of calibration.

Visual inspection: This method involves comparing the volume dispensed or aspirated by the pipette to a set of calibrated reference tubes or other containers. This method is suitable for most types of pipettes and is relatively quick and simple to perform.

Electronic calibration: This method involves using an electronic device to measure the volume dispensed or aspirated by the pipette. This method is suitable for most types of pipettes and is relatively quick and accurate.

This is a general protocol for calibrating a pipette using the gravimetric method:

  • Choose an appropriate weight standard and balance for the volume of liquid you will be calibrating. The weight standard should be traceable to a national or international standard.
  • Place the weight standard on the balance and tare the balance to zero.
  • Aspirate the known volume of liquid into the pipette.
  • Carefully dispense the liquid onto the balance pan and allow it to drain completely.
  • Record the weight of the liquid on the balance.
  • Calculate the density of the liquid by dividing the weight of the liquid by its volume.
  • Compare the density of the liquid to the known density of the liquid. If the density is within the acceptable tolerance for the pipette, the pipette is considered calibrated. If the density is outside the tolerance, further adjustments to the pipette may be necessary.

Applications:

DNA and RNA isolation and purification: Pipettes are used to transfer small volumes of DNA or RNA samples during the isolation and purification process.

Drug formulation and analysis: Pipettes are used to measure and transfer precise volumes of drugs and other chemicals during the formulation and analysis process.

Clinical testing: Pipettes are used to transfer small volumes of biological samples, such as blood or urine, during clinical testing.

Environmental testing: Pipettes are used to measure and transfer small volumes of water, soil, and other environmental samples for testing and analysis.

Food and beverage testing: Pipettes are used to measure and transfer small volumes of food and beverage samples for quality control and testing.

Industrial processes: Pipettes are used to measure and transfer small volumes of chemicals and other materials during various industrial processes.

Precautions:

  • Wear appropriate personal protective equipment (PPE), including lab coat, goggles, and gloves, to protect yourself from spills and splashes.
  • Follow proper pipetting technique to ensure accurate and consistent results. This includes using the correct size pipette for the volume being measured, holding the pipette properly, and using the pipette with the correct technique for the type of liquid being transferred.
  • Keep the pipette clean and well-maintained. This includes regularly cleaning the pipette and replacing any damaged or worn parts.
  • Use the pipette only for its intended purpose and in accordance with the manufacturer’s instructions.
  • Store pipettes properly to prevent contamination or damage. This may include storing pipettes in a designated area, away from heat and moisture, or in a protective case.
  • Dispose of pipettes and other laboratory waste properly to prevent contamination and protect the environment.
  • Follow all relevant safety guidelines and procedures in the laboratory, including handling hazardous chemicals and materials safely.

Limitations:

Accuracy: While pipettes are designed to be accurate, the degree of accuracy can vary depending on the type of pipette and the technique used. Factors that can affect accuracy include the size of the pipette, the viscosity of the liquid being measured, and the skill of the user.

Volume range: Different types of pipettes are designed to measure and transfer different volume ranges. It is important to use the correct size pipette for the volume being measured to ensure accuracy.

Liquid compatibility: Some pipettes are only compatible with certain types of liquids. It is important to use the correct pipette for the type of liquid being transferred to prevent damage to the pipette and ensure accuracy.

Maintenance: Pipettes require regular maintenance and calibration to ensure accuracy. This includes cleaning, replacing worn or damaged parts, and regular calibration.

Time and effort: Using pipettes can be time-consuming, especially when transferring small volumes of liquid. It is important to plan ahead and allow sufficient time for pipetting tasks.

Cost: Pipettes can be expensive, especially high-precision models. This may limit their use in some settings or for certain applications.

References:

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