A micropipette is a precision laboratory instrument used for accurately measuring and transferring very small liquid volumes, typically in the microliter range. These tools are indispensable across various scientific fields, including biology, chemistry, and medicine, where precise liquid handling is fundamental. Proper use of micropipettes is crucial for obtaining accurate and reproducible results in experiments.
Micropipette Components and Preparation
A micropipette consists of several distinct parts, each with a specific function. The plunger button, located at the top, controls both the aspiration and dispensing of liquids, and also helps in volume adjustment. The volume adjustment knob allows users to precisely set the desired liquid volume, which is then displayed in a digital window. A tip ejector button, often found near the plunger, facilitates the safe and clean removal of used pipette tips, preventing contamination. The main body houses the internal mechanisms, leading down to the shaft and tip cone, where disposable pipette tips are securely attached.
Micropipettes come in various types, designed to suit different laboratory needs. Fixed-volume micropipettes dispense a single, constant volume, useful for repetitive tasks requiring high precision. Adjustable-volume micropipettes offer flexibility, allowing users to select volumes within a defined range. Single-channel micropipettes handle one sample at a time, while multi-channel versions (typically 8 or 12 channels) can simultaneously aspirate and dispense liquids into multiple wells, useful for techniques like ELISA assays. Before liquid transfer, select the correct pipette for the desired volume and firmly attach a clean disposable tip to the tip cone.
Mastering Micropipette Technique
Accurately setting the volume is a foundational step in mastering micropipetting. For adjustable volume micropipettes, set the desired volume by rotating the volume adjustment knob until the numerical display shows the correct value. Ensure the volume is within the pipette’s specified range and avoid setting it beyond its upper or lower limits. Some models may have a lock mechanism to prevent accidental volume changes, requiring a slight lift or specific action to adjust.
Aspirating liquid correctly involves precise actions to ensure accuracy and prevent air bubbles. First, press the plunger down smoothly to the first stop, a point of resistance indicating the set volume of air has been displaced. While holding the plunger at this first stop, immerse the pipette tip slightly into the liquid (typically 2-6 millimeters below the surface, depending on volume). Then, slowly and steadily release the plunger, allowing the liquid to draw into the tip without splashing or forming air bubbles. Keep the pipette held vertically during aspiration to maintain accuracy.
Dispensing the liquid requires a controlled technique to ensure complete transfer and prevent contamination. After aspiration, move the pipette to the receiving vessel. Press the plunger down smoothly to the first stop to expel most liquid.
Continue pressing the plunger down to the second stop, which expels any remaining liquid from the tip, often with a small burst of air. During dispensing, touching the tip against the inner wall of the receiving vessel at a slight angle can help release residual liquid. Remove the tip from the vessel before releasing the plunger from the second stop.
Once the liquid has been transferred, the used tip must be ejected safely and cleanly. Position the pipette over an appropriate waste container, such as a biohazard bin. Then, press the tip ejector button firmly to release the disposable tip without direct hand contact. This practice minimizes the risk of cross-contamination and ensures laboratory safety.
Tips for Accuracy and Maintenance
Achieving consistent accuracy with micropipettes involves avoiding common errors. Pipetting too quickly, during aspiration or dispensing, can lead to inaccurate volumes, splashing, or air bubbles. An inconsistent pipetting angle (exceeding 20 degrees from vertical) can also cause volume discrepancies.
Using an incorrect tip size or one that does not fit snugly can result in leaks and unreliable measurements. Variations in temperature between the pipette, tip, and liquid can affect volume; allow all components to equilibrate to room temperature. To prevent cross-contamination, always use a fresh, sterile tip for each new sample or reagent.
Proper maintenance extends the lifespan and ensures the continued performance of a micropipette. Regularly cleaning the external surfaces, especially the tip cone and plunger, with a mild detergent or 70% ethanol, helps maintain hygiene and prevents build-up. Storing micropipettes vertically on a dedicated stand protects them from physical damage and prevents liquids from entering the internal mechanisms. While users do not typically perform internal calibration, professional calibration and servicing are necessary to verify and adjust the pipette’s accuracy and precision. Manufacturers generally recommend professional calibration at least every 12 months, though more frequent checks, such as every 3 to 6 months, may be advisable for pipettes used daily or in critical applications.