A pipette is a fundamental laboratory tool designed for the precise measurement and transfer of specific liquid volumes. Its ability to handle minute quantities of fluids with accuracy is important across various scientific disciplines, including chemistry, biology, and medicine. From preparing solutions for diagnostic tests to conducting rigorous experiments in research, pipettes ensure the reliability and reproducibility of results. The meticulous handling of liquids is paramount in laboratory settings, making the pipette an indispensable instrument for maintaining experimental integrity.
Understanding Your Pipette
The air-displacement micropipette operates on piston-driven air displacement, creating a vacuum within the shaft to aspirate and dispense liquids. A key feature of this design is that the liquid never directly contacts internal components, as an air cushion separates the piston from the liquid. This air cushion allows for contamination-free handling and contributes to precision.
A typical air-displacement micropipette features several components. The plunger button controls both aspiration and dispensing of liquid. A volume adjustment dial allows users to set the desired liquid volume, displayed in a digital window. The tip ejector button provides a convenient way to remove disposable pipette tips without manual contact, preventing contamination. Finally, the shaft connects to the disposable tip.
Step-by-Step Pipetting Technique
Proper pipetting begins with selecting a clean, disposable tip compatible with your pipette and gently securing it onto the shaft for an airtight seal. Adjust the volume by rotating the volume adjustment knob until the desired measurement displays. It is important to set the volume before attaching the tip to minimize accidental changes.
To aspirate liquid, depress the plunger smoothly to the first stop. While holding the plunger at this position, immerse the pipette tip slightly below the liquid’s surface (typically 2-6 mm) to avoid drawing up air or coating the tip exterior. Slowly release the plunger to draw liquid into the tip, waiting a second or two for full entry. Maintaining a consistent, nearly vertical angle (no more than 20 degrees) during aspiration helps ensure accuracy.
For dispensing, move the pipette to the receiving vessel and place the tip against the inner wall at a slight angle. Smoothly press the plunger to the first stop to dispense most liquid. To ensure complete expulsion, press the plunger further to the second stop (the “blow-out” position), holding until all liquid is released. Do not release the plunger until the tip is removed from the receiving vessel, then eject the used tip into an appropriate waste container.
Ensuring Accuracy and Avoiding Common Mistakes
Achieving accurate pipetting results depends on several factors. Environmental conditions, such as temperature, humidity, and air pressure, can influence pipetting accuracy. Temperature differences between the pipette, tips, and liquid can affect the air cushion volume, leading to measurement variations. Allowing these components to equilibrate to room temperature can help mitigate such issues.
Common errors that can compromise accuracy include improper tip immersion and inconsistent plunger speed. Immersing the tip too deeply can lead to liquid clinging to the outside, while insufficient immersion risks aspirating air, resulting in inaccurate volumes. Rapid or jerky plunger movements during aspiration can cause air bubbles or splashing, affecting transferred volume. Failing to pre-wet the pipette tip by aspirating and dispensing the liquid a few times can lead to volume variations, particularly with volatile liquids, as it helps condition the tip and reduces evaporation.
Other factors that impact accuracy include the liquid’s viscosity and volatility, as these properties can influence how much liquid adheres to the tip or evaporates. Using the correct pipette for the specific volume range is important, as pipettes are most accurate within their optimal operating range (typically 35-100% of their nominal volume). Selecting high-quality, compatible tips that fit securely to prevent leaks is another important step to ensure reliable performance.
Proper Care and Maintenance
Consistent care and maintenance are important for prolonging a pipette’s lifespan and maintaining its accuracy. Regularly cleaning the external surfaces with a mild detergent or lab-grade disinfectant helps prevent contamination. Wipe the pipette shaft and other external parts with a lint-free cloth, following manufacturer guidelines, and avoid submersion in liquids.
Proper storage is important; pipettes should be stored upright on a stand or rack when not in use to prevent liquid accumulation in the shaft and to protect them from damage. Resetting adjustable pipettes to their maximum volume setting when stored can help relieve stress on internal springs. Regular visual inspections for signs of damage or corrosion, such as cracks or a crooked plunger, can identify issues early that might affect performance.
Routine calibration is recommended to ensure pipettes continue to dispense accurate volumes. Clinical and GLP (Good Laboratory Practice) labs often follow protocols for calibration every 3 to 6 months, while general guidelines suggest at least annually, depending on usage frequency and application sensitivity. Calibration verifies that the instrument dispenses the correct volume and helps address any deviations, ensuring consistent and reliable results.