It is crucial to be able to pipette accurately. Inaccurate pipetting would result in poorly reproducible experiments and inaccurate stock solutions. It would also make comparisons of assays meaningless. Accurate pipetting is dependent on the user's technique and the precision of the instrument. If the device is used improperly, too much liquid may be dispensed, resulting in inconsistent results.
When using a micropipette tip, it is important to understand the difference between the soft and hard stops. The soft stop prevents the tip from filling with too much liquid. The hard stop forces air out of the tip and gathers more sample than the indicated volume on the volume setting window. It is best to use a hard stop when obtaining a sample.
Incorrect tip depth may cause the pipetting process to fail. Deep tips can cause excessive aspiration by allowing more liquid to enter the tip than is required. The risk of carrying over liquid is proportional to the surface area of the pipette tip. A deep tip can cause a problem as it increases the amount of hydrostatic pressure. Overcontacting the tip can also lead to overdelivery of the sample.
When you are using a micropipette, you should never aspirate the liquid into it unless you have a proper tube. This will damage the inside of the tube, causing it to need to be calibrated or repaired. Besides causing the pipette to break down, too much liquid can also cause inaccurate results. When this happens, it's best to use a different type of pipette.
There are two types of micropipettes. Positive displacement micropipettes operate by placing a piston in direct contact with the liquid. These tips aspirate the liquid into the tip and draw the liquid back into the pipette body. However, if the amount of liquid is too small, it can cause the pipette to fail. If the volume is too large, the tip will break. Those with fixed volume settings and those with variable volume settings. Some have an upper and lower limit and an error percentage based on the liquid. The lower limit limits the amount of liquid that should be dispensed while the upper range defines the volume of the sample. The upper range, on the other hand, is the minimum amount that should be dispensed. If the lower range is set too low, the sample will be inaccurate and more will enter the pipette body.
There is the soft stop, which is used when the sample is too small to be detected. The hard stop is used for experiments where the liquid concentration is too high, as the air will cause the sample to leak out. A hard stop will only cause a sample to flow more than what the volume settings indicate. If you have a softer tip, you can just leave it in place while you are conducting the experiment.
If too much liquid gets into a micropipette tip, you should immediately rinse the device and reinstall the tip. After cleaning, ensure that the pipette has not been damaged by the liquid. If it is, it needs to be calibrated again. It should be safe to re-use it for the same purpose. Once the tips are repaired, it will be more accurate.
Some micropipettes have a fixed volume setting, while others have adjustable volume settings. These types will have upper and lower limits. You should never attempt to disperse more liquid than the lower limit. You will have too much liquid. If you don't want too much, try to dispense less liquid or more. If you are not sure of the amount of liquid you need, make adjustments accordingly.