A pipette is a fundamental laboratory tool designed for the precise measurement and transfer of small liquid volumes. It plays a central role in scientific and medical settings, facilitating the accurate handling of reagents, samples, and solutions. This instrument is indispensable across various disciplines, from chemical analysis to biological research, where the exact quantity of a liquid can significantly impact experimental outcomes.
What is a Pipette?
At its core, a pipette operates by creating a partial vacuum to draw liquid into a tube and then releasing that vacuum to dispense it. The basic structure includes a main body or housing, a mechanism for drawing and expelling liquid, and a tip or nozzle that comes into contact with the liquid. This design allows for the accurate handling of volumes ranging from microliters (µL) to milliliters (mL). The accuracy of volume measurement is a defining characteristic of these devices.
The internal mechanics of many pipettes involve a piston that moves within an airtight sleeve. When the plunger is depressed, air is expelled, and upon slow release, a vacuum is created, drawing the liquid into a disposable tip. This mechanism ensures a specific, measured volume of liquid is aspirated. Different types of pipettes handle various liquid properties and volume requirements.
Common Types of Pipettes
Several common types of pipettes exist, each suited for particular laboratory needs based on volume, accuracy, and application. Volumetric pipettes, also known as bulb pipettes, are distinguished by their single calibration mark and a large bulb in the middle. These pipettes deliver a single, fixed volume with high accuracy, making them ideal for preparing stock solutions or for titrations.
Graduated pipettes, sometimes referred to as serological or Mohr pipettes, feature a series of calibration marks along their length, allowing users to dispense various volumes. While more versatile in volume selection than volumetric pipettes, they offer a lower level of precision. These are commonly used for general liquid transfers, mixing reagents, or handling cell culture media, where exact single-volume delivery is not the primary concern.
Micropipettes are specialized instruments for handling very small liquid volumes, typically in the microliter range. They include air displacement micropipettes, which use an air cushion, and positive displacement micropipettes, where the piston directly contacts the liquid. Micropipettes can be fixed-volume, dispensing one specific amount, or adjustable-volume, allowing the user to select from a range. Multichannel micropipettes, which aspirate and dispense liquid from multiple tips simultaneously, are also available for high-throughput applications like filling microplates.
How Pipettes Are Used
Using a pipette correctly involves a series of steps to ensure accurate and contamination-free liquid transfer. The initial step involves selecting the appropriate disposable tip for the pipette and securely attaching it to the shaft. For adjustable volume pipettes, the desired volume is then set using a dial or knob, ensuring it falls within the calibrated range.
To aspirate liquid, the plunger is depressed to the first stop before the tip is immersed slightly into the liquid. Slowly releasing the plunger draws the liquid into the tip; ensure no air bubbles are present, which could indicate an inaccurate volume. Once drawn up, the tip is carefully withdrawn from the source liquid.
Dispensing the liquid involves placing the pipette tip against the side wall of the receiving container. The plunger is then depressed to the first stop to release most of the liquid, followed by pressing to the second stop to expel any remaining droplets. After dispensing, the used tip is safely ejected into a waste container using the tip ejector button. Proper technique, including maintaining a vertical pipette angle and avoiding deep immersion of the tip, helps ensure accuracy and prevent cross-contamination.
Why Pipettes Are Essential
Pipettes are important tools in scientific, medical, and research fields, valued for their precision and accuracy. Their ability to measure and transfer minute volumes with exactness ensures the reliability and reproducibility of experimental results. In fields such as molecular biology, pharmacology, and clinical diagnostics, even slight variations in liquid volumes can lead to significant errors, making accurate pipetting necessary for valid outcomes.
The controlled transfer facilitated by pipettes helps prevent contamination, important in sensitive biological and chemical processes. This capability helps maintain the integrity of samples and reagents, supporting complex procedures like Polymerase Chain Reaction (PCR) and DNA sequencing. Pipettes also facilitate accurate diagnostic tests, where precise measurements directly impact patient care and treatment decisions. Their widespread use supports quantitative analysis across various scientific disciplines.