A micropipette is a commonly used instrument in laboratories that can accurately absorb and discharge minute amounts of liquid to achieve quantitative transfer of liquid. The standard use of micropipette is related to the accuracy of the required liquid volume and the service life of the micropipette. Therefore, it is necessary to operate the micropipette in a standardized manner. Below, I will take the double dilution of the tested serum on a 96-well microplate as an example, starting from the selection of pipettes, volume adjustment, tip installation, tightness inspection, liquid suction and discharge, tip removal, transfer This article summarizes how to standardize the use of adjustable single-channel micropipette from eight aspects including liquid container organization.
Selection of pipette: Choose the appropriate pipette according to the experimental needs. Generally speaking, the volume of the pipette should match the required liquid volume, that is, the liquid volume should account for 50% to 100% of the pipette volume. For example, if you need to pipet 100 μL of liquid, you should choose a 100 μL or 200 μL pipette instead of a 1000 μL pipette to ensure the accuracy of pipetting.
Volume adjustment: Before using the pipette, adjust the volume of the pipette so that it is consistent with the required liquid volume. When adjusting, the adjustment knob should be rotated from large to small or small to large according to the scale on the pipette until the desired value is reached. When adjusting, be careful not to exceed the maximum or minimum volume of the pipette, otherwise the internal structure of the pipette will be damaged.
Suction head installation: After adjusting the measuring range, a suitable suction head should be installed. The size of the tip should match the capacity of the pipette, that is, the capacity of the tip should be greater than or equal to the capacity of the pipette. For example, if you use a 100 μL pipette, you should choose a 100 μL or 200 μL tip instead of a 20 μL or 1000 μL tip to avoid liquid overflow or incomplete aspiration. When installing the tip, gently press the pipette's piston rod to the first position, and then insert the tip vertically into the pipette's tip holder until you hear or feel the tip connecting. The sound or feeling of a close bond.
Tightness check: After installing the tip, check the tightness of the pipette, that is, whether there is air leakage. The inspection method is to gently press the piston push rod of the pipette to the first gear, then immerse the tip in pure water, release the piston push rod, and observe whether there are bubbles in the tip. If bubbles are produced, the pipette is leaking and the tip or pipette should be replaced. If no bubbles are generated, the pipette is tightly sealed and can continue to be used.
Liquid suction and discharge: After checking the tightness, liquid suction and discharge can be carried out. When aspirating liquid, gently press the piston rod of the pipette to the first position, and then immerse the tip into the liquid. The liquid level should be higher than the lower end of the tip. Then, slowly and evenly release the piston push rod so that the liquid is sucked into the tip. The liquid level should be consistent with the scale on the pipette. If the liquid level is too high or too low, re-aspirate.
After aspirating the liquid, the pipette should be lifted vertically to prevent the liquid from flowing down along the outer wall of the tip, causing errors. When discharging liquid, the tip should be brought into contact with the inner wall of the target container, and then the piston rod of the pipette should be pressed to the second gear quickly and evenly to completely discharge the liquid. Then, slowly and evenly release the piston push rod of the pipette to its original position to avoid negative pressure that may cause liquid to be sucked back. After discharging the liquid, the pipette should be lifted vertically to prevent the tip from adhering to the inner wall of the target container, causing errors.
Tip removal: After completing the liquid transfer, the tip should be removed to avoid contamination of the pipette or the liquid. When removing the tip, gently press the piston push rod of the pipette to the first position, then aim the tip at a discarded container, and press the tip removal button on the pipette to make the tip automatically fall off. After removing the tip, the piston push rod of the pipette should be loosened to its original position to avoid damaging the internal structure of the pipette.
Pipette neatness: After removing the tip, the pipette should be placed neatly to maintain the performance and life of the pipette. When placed neatly, the pipette's range should be adjusted to its maximum value to reduce the spring pressure on the piston. Then, place the pipette on a special stand or rack to avoid placing the pipette upside down or horizontally, causing liquid residue or dust to enter the inside of the pipette. In addition, pipettes should be cleaned and calibrated regularly to ensure their accuracy and stability.
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