Introduction and Key Features
1. Basic Structure:
Sterile, Disposable: Most modern serological pipettes are made of polystyrene and come individually wrapped in a sterile package for use in aseptic techniques.
Graduated Scale: Features calibrated volume markings along its length. Two main types exist:
To Deliver (TD): Calibrated to deliver the specified volume when the liquid is drained by gravity (or slight blow-out, depending on type). Most common.
To Contain (TC): Less common for serological pipettes; calibrated to contain the volume, requiring rinsing to deliver the full amount.
Printing: Clearly displays the total volume (e.g., 10mL), graduation increments, and often a color-coded band for quick identification.
Distinguishing Feature -Vented/Filtered or Non-Filtered:
Vented/Filtered Pipettes: Have a cotton or aerosol barrier plug near the mouthpiece. This prevents contamination of the pipette controller and is essential for sterile work with biological fluids and cell culture.
Non-Filtered Pipettes: Lack this barrier. Used for non-sterile work or with non-hazardous chemicals.
II. Step-by-Step Usage Guide (Aseptic Technique)
Equipment Needed: Sterile serological pipette, Pipette Controller (manual bulb, electric/green Pipet-Aid), waste container, sterile reagent bottle, lab coat, gloves.
Procedure:
1. Preparation:
Ensure your work area (e.g., laminar flow hood) is clean and disinfected.
Have all materials within easy reach.
Check the pipette packaging for integrity and expiry date.
2. Selecting and Opening the Pipette:
Choose the pipette size with the appropriate range and accuracy for your volume. For example, use a 5mL pipette to transfer 4.5mL, not a 25mL pipette.
Tear open the wrapper at the notch or designated opening point.Do not completely remove the pipette; expose only the mouthpiece end.
For Vented Pipettes: Attach the exposed mouthpiece securely to the pipette controller.
3. Aspirating Liquid:
Hold the pipette controller vertically. Immerse the pipette tip into the liquid to an appropriate depth (a few millimeters) to avoid aspirating air.
Press the controller's aspiration button or squeeze the bulb.Aspirate slightly above your desired final volume to account for the meniscus.
Pause briefly to allow liquid to settle. Keep the pipette vertical.
4. Reading the Meniscus:
This is critical for accuracy. The liquid forms a curved surface (meniscus).
Read the volume at the bottom of the meniscus (the lowest point of the curve), aligning it with the graduation line at eye level.
To adjust to the exact volume, carefully expel excess liquid back into the source container or a waste beaker.
5. Dispensing Liquid:
Touch the pipette tip to the inner wall of the receiving vessel (e.g., flask, plate well) at a slight angle.
Two Dispensing Techniques:
Gravity Drainage: Press the controller's slow/variable-speed dispense button to allow liquid to drain by gravity. This is standard.
Blow-Out: Many serological pipettes (marked with a frosted ring or double ring near the top) are calibrated to deliver the full volume only when the last drop is "blown out" using the controller's rapid/blow-out function.Check the pipette marking.
To ensure complete delivery, slide the tip up the vessel wall as you finish dispensing.
6. Discarding:
Place the used pipette directly into a container filled with appropriate disinfectant (e.g., 10% bleach) or a sharps/bin for plastic waste. Do not recap or reuse.