Immerse the tip to the proper depth Before aspirating, immerse the tip adequately below the meniscus. Body heat transferred during handling disturbs temperature equilibrium, which leads to variations in delivered volume.Ĩ. Avoid handling pipette tips, or containers of liquid to be pipetted. Minimize handling of the pipette and tip Hold the pipette loosely, return it to the pipette stand or set it down between deliveries. Touching the sides of the container causes wicking and loss of volume.ħ. Holding the pipette at an angle as it is removed from the liquid alters the volume aspirated. This technique is especially important when pipetting small volumes (less than 50 µL). Pull the pipette straight out When aspirating, hold the pipette vertically and pull the pipette straight out from the center of the container. Pausing consistently balances these two effects and ensures correct aspiration.Ħ. At the same time, evaporation within the tip is occurring. Liquid continues to flow into the tip for a short time after the plunger stops. Make this pause as consistent as possible. Pause consistently after aspiration After aspirating, and before removing the tip from the liquid, pause for one second. Reverse mode often results in over-delivery.ĥ. Standard (or forward) mode pipetting yields better accuracy and precision than reverse mode for all but viscous or volatile liquids. Remove the pipette from the liquid and depress the plunger to the second stop to dispense the entire contents. Use standard mode pipetting Depress the plunger to the first stop, immerse the tip into the liquid and aspirate by releasing the plunger. Surface tension will help draw the remaining liquid out of the tip.Ĥ. After dispensing, and before releasing the plunger, deliver any residual liquid remaining in the tip by touching the tip to the side of the container. Examine the tip before and after dispensing sample Before dispensing, carefully remove droplets on the outside of the tip with a lint-free cloth, being sure to stay clear of the tip opening to avoid wicking liquid out of the tip. Working at a constant temperature minimizes variation of pipetted volume.ģ. The volume of liquid delivered by air displacement pipettes varies with relative humidity and vapor pressure of the liquid - both of which are temperature-dependent. Work at temperature equilibrium Allow liquids and equipment to equilibrate to ambient temperature prior to pipetting. Prewetting increases the humidity within the tip, thus reducing evaporation.Ģ. Failure to prewet increases evaporation within the tip air space, which can cause significantly lower delivery volumes. Prewet the pipette tip Aspirate and fully expel an amount of the liquid at least 3 times before aspirating for delivery. Of all the factors contributing to the performance of a pipette, the most critical are the skill and expertise of the operator.ġ.
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